If you have a less-than-perfect lens, you might find that stopping down the lens aperture can substantially change the amount of that nasty color fringing at the edges of the frame. The MTFMapper v7.29 program has some very sophisticated features to measure that color fringing (lateral chromatic aberration), also nicknamed “CA”. Lateral Chromatic Aberration CA is the ugly color fringing that you see in the frame edge when you photograph, for instance, tree branches against the bright sky. You may not notice it when you switch to a really good lens or stop the aperture down enough. The color of this aberration can vary considerably, depending upon your lens. Those color fringes are caused by the lens not bending the different colors of light equally; a ‘white’ light ray gets spread across a region of the sensor, instead of being kept as a point. This is different than axial chromatic aberration, where the different colors of light remain aligned relative to the lens axis, but get focused at different distances from the sensor plane. Many cameras will attempt to automatically remove CA, if you shoot in jpeg mode. Most modern photo editing programs will let you reduce, if not eliminate it, even if you shoot in Raw format. This CA removal usually costs you in resolution, especially at the frame edges. Lens reviews on the web lead you to believe that CA is a single number for a given lens, aperture, and sensor edge. False. To understand the true character of this lens defect, you can use MTFMapper, but only if you shoot in Raw format. You also need to use a suitable target. The same website that lets you download MTFMapper has files of resolution charts that you can print. Uncorrected Lateral Chromatic Aberration from a Poor Lens, Widest Aperture. The shot above shows how bad it can get with CA. This is example from a super-wide lens in the corner, and without any corrections applied. Suitable chart to use for your photographs The chart above shows you what a suitable target looks like. The bigger you can print it, the better. Wide-angle lenses particularly need large charts to get good feedback at realistic shooting distances (mine is 3 feet by 4 feet). Nikkor 85mm f/1.4 AF-S Lateral Chromatic Aberration In the testing that follows, I chose my 85mm f/1.4 lens. This lens was tested using a Nikon D610 that has an FX sensor with 5.95 micron pixels. The camera sensor pixel size needs to be entered into the program, or else the measurements will be incorrect. I am using the “micron measurements” program option, instead of the “pixels” or “radial offset percent” options. I use this option, so that it’s easier to directly compare measurements from other lenses or cameras. Nikkor 85mm f/1.4 with Nikon D610 (FX) Measurements at f/1.4 show many interesting things. First, notice how non-symmetric the readings are. Secondly, notice that the “Red versus Green” measurement range is entirely different than the “Blue versus Green” measurements. Nikkor 85mm f/2.0 with Nikon D610 (FX) Nikkor 85mm f/2.8 with Nikon D610 (FX) Nikkor 85mm f/4.0 with Nikon D610 (FX) Nikkor 85mm f/5.6 with Nikon D610 (FX) Nikkor 85mm f/8.0 with Nikon D610 (FX) Nikkor 85mm f/11.0 with Nikon D610 (FX) Nikkor 85mm f/16.0 with Nikon D610 (FX) Conclusions I found it interesting that the color shifting actually changed direction with the Blue/Green pixels, going from positive to negative, after stopping down to f/2.8 or beyond. I realize that every lens design may have unique characteristics, but it had never occurred to me that CA might have a cross-over response to aperture. This analysis is just one lens. The intent is to show you how an arbitrary lens can be evaluated to explore its limitations, at least in regards to chromatic aberration. The MTFMapper program has many additional capabilities, most notably resolution analysis in two dimensions. The 85mm’s Red/Green CA is essentially imperceptible at any aperture and very different than the Blue/Green response. Most lenses probably favor one color pair over the other. This is probably a good test to spot poor lens assembly or damaged lenses. Plots that aren’t reasonably balanced about the lens optical center could be easy to spot, indicating a problem such as a tilted lens element. As I suspected, stopping down the aperture definitely helps reduce CA, at least for this 85mm lens. The whole point in using the free MTFMapper is to enable photographers to evaluate their own lens characteristics. Since this feature has just become available in MTFmapper, I have a lot of exploring to do. Any broad conclusions I draw from studying a single lens will probably require many future revisions. This new CA feature has definitely given me extra food for thought.

This review is mostly concerned with the lens MTF50 resolution performance and how well the lens autofocuses. I’m not overly concerned with minor lateral chromatic aberration (since the software fixes it), trivial distortion (software can fix it), and some vignette issues for full-frame users (software can fix it, too). What software can’t fix is a lens that focuses poorly or has weak resolution. The Sigma 150-600 Contemporary lens delivers where it counts. All across the field of view. And it delivers with the aperture wide open (which is pretty much where I park it). This is a “single lens copy” test, so your mileage may vary. I know, you’re suspicious that the Contemporary resolution is garbage compared to the Sports version; read on. I’ve spent the better part of my life wanting a really big lens that wasn’t crap or cost as much as a car. Here it is. It’s liberating to frame a subject the way I want, and actually have some elbow room in focal length left over. For those of you that want to shoot eagles in a dive with a 600mm prime lens, good luck finding it looking through an 11-pound straw. You want a zoom to find the thing and then zoom in. This is among the smartest lenses on the planet to date. Don’t get this lens without the Sigma USB dock and its Optimization Pro program; you’ll regret it if you do. The dock will let you properly calibrate focus at 16 combinations of focal length and distance; all zooms need this capability, but all of the other manufacturers have done nothing about it to date. If you read a review mentioning something like "it focuses well at 40 feet but not infinity" then that probably means that they didn't bother to carefully calibrate the lens at each focal length and distance setting using the Sigma USB dock. Don't be lazy! I hope you’re ready for a 4 1/2-pound lens, though (with hood). I can’t imagine hauling around the ‘Sports’ version all day, which is about 7 pounds (with hood). You might try renting a beast like the Sports version and carry it for a whole day before you buy it. Maybe you shoot in rain and dust all the time and need the Sports version; it’s a heavy price to pay, though. Sorry about the pun. I mostly bring a monopod with a gimbal head and an Arca-Swiss plate when shooting animals. You can shoot all day, properly balance the lens at every focal length, and most importantly not suffer while trying to hold this thing steady. I have lasted maybe an hour with the lens hand-held before I was ready to call it quits. I typically use the “OS2” stabilization setting (panning) instead of “OS1” (general hand-held) in poor lighting on a monopod. If I move the lens both vertically and horizontally, though, then I need "OS1" set (until about 1/1000 second, beyond which it should be turned off). The lens center of gravity shifts quite a bit while zooming, hence the Arca-Swiss plate. 3-17-2017 Update After the firmware update from Sigma (using the optional USB dock) you no longer need to turn off optical stabilization when using high shutter speeds. Yes, you’ll need to stop using ISO 100 with this lens. Get over it. Even the people shooting with the $10K+ super telephotos have gotten over it. Learn to love f/6.3. Here’s a word or two about “plastic”. Some of the finest and most high-tech materials in the world are plastic. They didn’t make this lens out of melted milk jugs. They use thermally stable composite; it’s tough and has excellent dimensional properties, even over a wide range of temperatures. And it makes the lens light enough that you can actually walk around with it. I used to be jealous of those guys with the little wheels on their tripods and their 400mm f/2.8, 10 pound lenses. Careful what you wish for. Just don’t drop the lens. Same goes with metal lenses; drop a big lens on the sidewalk and it’s a goner, period. I don’t see too many plastic football helmets breaking, and I don’t see too many “quality metal” football helmets, either. Sigma gives you a neck strap that attaches to the tripod collar. It might seem a little geeky, but it is a great insurance policy. I use it, especially when I’m adjusting the monopod leg when it’s attached. And never, ever hold this rig by the camera; bad things will happen. I also use a Cotton Carrier to carry the lens on a waist belt when I’m not going to be shooting for a while; it totally saves your back and neck. The lens comes with a zoom lock, so it won’t creep out to 600mm while you’re walking with the lens pointed down on the waist belt; it doesn’t creep getting a moon shot over head if you lock it, either. Nice. The lens hood is bayonet, which is always my favorite. It reverse-mounts for storage, which is exactly what you want. The lens is breathtakingly long at 600mm with the hood on, but what did you expect? You always want to use the lens hood; the longer the focal length, the more important it is to use the hood. Lots of glass in that lens. You also get a pretty nice storage case with the lens. I swear that the Sigma designers must actually use their lenses. What a concept. You have to wonder about some of the other manufacturers. One note about the zooming. It’s Canon-standard direction and opposite the Nikon-standard. Not much of a problem when you’re sticking with one lens, but muscle memory goes haywire when using another lens on the same day. Sigma even offers a service to change the lens mount if you have a mid-life crisis and switch from Canon to Nikon or whatever. It’s my understanding that Canon and Nikon do not offer this service. Duh. Sigma 150-600 Contemporary at 600mm on gimbal head Lens was elevated a little higher than ideal in the gimbal so you can see it better. Properly balanced using Arca-Swiss plate. Note the supplied neck strap Autofocus I prefer to use the camera in AF-C mode and a separate focus button. This lens focuses quickly with absolutely no chatter using the factory default AF algorithm. Lenses with focus chatter (like my Nikkor 70-300 AF-S) drive me crazy, especially with their auto-50%-un-sharp-rate. Three different autofocus algorithms are available with the Sigma Optimization Pro and USB dock. Choose between Speed Priority, Standard (factory), or Accuracy. I wasn’t happy with the repeatability of Speed Priority, and the factory setting works very well for me. I’m leaving this customization alone and sticking with the factory setting. I have, as a matter of fact, assigned “C1” to be Speed Priority and “C2” is Accuracy, but I am presently leaving this custom switch OFF, to get the factory default Standard setting. Sigma is bound to optimize their autofocus algorithms more in the future, so I may re-evaluate my decision to avoid using Speed Priority. You’ll probably want to use the “Focus Limiter” switch to get a more substantial speed-up of autofocus without sacrificing accuracy or repeatability. Just don’t forget when you decide to limit the focus range. I’ve missed several shots when a subject moved just outside the range setting. Update 3/21/2016 Sigma released new firmware that makes focus between 20% and 50% faster. I told you so. Sigma did it for FREE, too. The USB dock just paid for itself yet again. I tried it out, and the focus really snaps. My test shots (not new resolution test charts, though) don't show any obvious loss in sharpness with this speed increase. I found the focus motor to be remarkably quiet. Always a good thing. I focus-calibrate the lens and use the Sigma USB dock to save the data before I do any resolution testing. Tests are done with stabilization off, contrast-detect autofocus (mostly), and I use the infrared remote with the mirror up. I only use RAW, unsharpened pictures for measurements. Testing was done using a Nikon D7000. I have been amazed how close phase detect focus compares to contrast detect focus with this lens. Newer cameras will only be better. Sigma dock 16 focus calibration settings. Your settings will be different. It’s a ton of work to fill in the 16 calibration settings with verified values; there were iterations galore. You’ll thank yourself once it’s done, though; no pain no gain. Maybe some day Sigma can write these values for us at the factory, since they claim to measure every lens MTF anyway for quality control (I bet they don’t do it at all 16 combinations, though). Note that the “Rewriting” button above needs to say “Save”. I wonder how well I would do if I had to label the buttons in Japanese. Focus Limiter Range You can tailor the distance ranges applied to the Focus Limit switch using the USB dock. You probably don’t want to alter the “Full” range setting (minimum focus to infinity), but that’s just me. You might want to change the “10m-infinity” setting to actually use something like “5m-infinity”, though. The focus limit switch settings on long focal lengths can be pure gold for minimizing the time to acquire focus. I’d try this feature first before I’d look at the “Speed Priority” autofocus algorithm. Don’t take my word for it, though; try it for yourself. OS Setting (Vibration Reduction) Customization It claims to alter the amount of visible vibration reduction in the viewfinder (as opposed to actual sensor anti-shake). It presumably provides the same level of anti-shake effect in the actual photographs, regardless of the setting. Honestly I haven’t experimented with this, and the factory setting works well (but the subject does move around more in the viewfinder than I’m accustomed to seeing with Nikon VR in effect). Remember to always turn off the OS when shutter speeds go faster than 1/500 (or at least 1/1000). Do as I say, not as I do. The programmable settings are referred to as “Dynamic View”, “Standard”, and “Moderate View”. I’m personally able to get about 3 stops of shake reduction with the factory setting. Since I mostly use a monopod with this lens, I use the OS-2 (‘panning’) versus the OS-1 (‘normal’) mode in poor light. If I have any vertical motion, however, then the best setting is OS-1. Most reports suggest that the OS provides about 3 2/3 stops enhancement. I guess I shouldn’t have had that last cup of coffee before I tried this. I have found that the shutter range between 1/500 and 1/1000 is 'murky'. Generally I have better results with stabilization ON here; beyond 1/1000 shutter, active OS makes resolution drop about 9%. 3-17-2017 Update: The firmware update fixes the problem with using stabilization and high shutter speeds. It also increased focus speed. "Moderate View" gives the best stabilization effect, although "Dynamic View" provides the smoothest viewfinder effect. See my article here. I was correct about improvements in future firmware updates! This feature (finder view and sensor anti-shake) is likely to get improved in future firmware updates, since stabilization is a mix of both lens hardware and firmware algorithm cleverness. Resolution Testing I hate those lens reviews which grade lens resolution with adjectives like “good”, “fair”, and “excellent”. What the heck does that mean? I want real numbers and I want to see real pictures of things I’d actually bother to photograph. I want to see sharp eyes, fur, and feathers. Does the camera sensor matter? Yes! Tests shown below on a Nikon D7000 can be improved by about 20% by switching to the Nikon D7100, for instance (I tested it). I use a (free!) program called MTF Mapper from here to measure lens resolution. The download site also has files for printing out the resolution targets (mine are A0 size on heavy glossy paper, mounted on a board). This program is covered in more detail in another article, but suffice it to say that this is really great stuff; it’s comparable to ‘Imatest’ in the quality of the MTF measurements, and it uses the “slanted edge” technology similar to ‘Imatest’, also. The author of MTF Mapper, Frans van den Bergh, really knows his stuff. The MTF Mapper documentation he wrote works best for people with an IQ around 180 and above, I suspect. The "MTF" refers to Modulation Transfer Function, which refers to how light/dark transitions happen. "MTF50" refers to the highest line frequency (line pairs per millimeter) you can have before 50% of the contrast is lost. Values above about 30 lp/mm are considered pretty good, and anything above 50 lp/mm is outstanding. You can judge for yourself how the sample photos in this article relate to the MTF50 numbers I measured. Always keep in mind that this is just ONE lens sample; I guarantee your mileage will vary. Some physics facts first. The 600mm resolution isn’t going to be as good as 150mm, even if the optics are “just as good”. Vibrations are magnified and the extra atmosphere between the lens and the subject will cause a little shimmer. Just saying. The chart design used for resolution tests orients all of the little black squares to be ‘slanted’ but they’re generally aligned in meridional and sagittal (think spokes on a wheel) directions to correlate better with the usual MTF plots you’re familiar with. There’s often a dramatic difference in sharpness between these two directions, and the chart photographs show it clearly. The meridional/sagittal differences are what “astigmatism” is all about. This lens is better in the sagittal than the meridional direction when you get away from the lens optical center. BTW, there is a mild “X” pattern that shows up in many of the 2-D focus plots; Frans van den Bergh has shown this to be a consequence of the square shape of the photo sites on the camera sensor itself. The MTF50 values are only very slightly affected by this (about 2% error along the “X”). You can get a load of how smart Frans is by reading his discussion of this phenomenon here. You might want to grab a cup of Joe first. If you think that the resolution test values should match the manufacturer MTF plots, think again. You might want to consult Roger Cicala’s article here to get a rude awakening. BTW, Roger uses “tangential” instead of meridional terminology. What the resolution target looks like. You’re probably wondering by now if I’m ever going to get around to some actual resolution results. I am, but I just wanted to provide some background into why the resolution results have actual validity (for this particular copy of this lens model). I hate “secret science” and hand-waving claims. I guess it’s just the engineer in me (I’m a mechanical engineer and software developer). I want you to be able to do the same tests as me. Thanks again, Frans. 600mm f/6.3 Note peaks at almost 40 lp/mm Note the little red edge measurements in the plot. The sagittal measurements are quite a bit better than the meridional (tangent) measurements. Note the EXIF data shows this was shot at about 62 feet (18.8m). This is a pretty realistic distance for a focal length like this. Farther than most testers would attempt. Tests were done in “Live View”, contrast detect, IR remote. The 600mm f/6.3 test above was 1/640s, ISO 800, +0.7EV exposure compensation, lens vibration reduction OFF. This is approximately EV 12.3. All subsequent tests were ISO 800 to maintain high shutter speeds. Resolution on this camera drops off after about ISO 1600. 600mm f/6.3 whole field of view. Sagittal is better than Meridional 600mm f/8 resolution not much different 600mm f/6.3 Lens Center I know, I know. There’s a little crease in your chart! Fortunately, it didn’t have any effect on the measurements. 600mm f/6.3 APS-C Corner. Note Sagittal much better than Meridional 500mm wide open 500mm wide open 500mm f/8.0 500mm f/8.0 400mm f/6.0 A bit of a surprise seeing this much astigmatism here (look at the wide vertical spread on those data points). Nonetheless, pictures at this focal length look pretty nice to my eye. 400mm f/6.0 whole sensor 2D view It’s the meridional measurements on the sensor edges are bringing down the averages. The center is really, really sharp. 400mm f/8 400mm f/8 300mm wide open. Pretty awesome. 300mm f/5.6 Flirting with 50 The test chart A0 size wasn’t quite large enough to fill the frame at this distance. 300mm f/8. That’s what I’m talking about 300mm f/8 200mm wide open Note the distance change for 200mm and below. The chart is back to filling the frame. 200mm wide open 200mm f/8. Look at all those red specks over 50 200mm f/8 150mm wide open 150mm wide open 150mm f/8 awesomeness It’s a crying shame that I almost never use 150mm (except to locate the target before zooming in). I bet it would make stunning portraits, but depth of focus might be a bit too deep for my taste. 150mm f/8 Sample Pictures Cheetah Deep Shade 500mm f/6.0 1/250 ISO 2000 stabilization OFF Cheetah crop to see eye detail. Enough said. Grizzly 240mm f/5.6 1/200 ISO 1250 stabilization ON Hummer 480mm f/6.0 1/800 ISO 1000 stabilization OFF Lioness 440mm f/6.0 1/500 ISO 1600 stabilization ON Lion 600mm f/6.3 1/1000 ISO 1600 stabilization OFF. Nice background blur #review

This 2013 camera was the mirrorless version of the Nikon D7000 from 2010. I thought it would be interesting to take a look at this camera to see how it has fared with time. Let’s face it; most digital equipment ages very badly. The Coolpix A has the same DX sensor (except special micro-lenses on the pixels) and it actually cost about the same ($1,100 US) versus the D7000 ($1,200) when it was new. I’m not much of a fan of this kind of camera design, for a couple of reasons. The Coolpix doesn’t have a viewfinder; it only has an LCD screen (very, very bad for action or sunshine photography). The Coolpix also has a fixed 18.5mm f/2.8 lens; you can’t zoom it or interchange it with anything else. You also can’t put any filters on the lens, unless you buy an adapter to fit 46mm filters. The field of view is equivalent to a 28mm lens on FX. I have an LCD viewfinder (made by Xit) that I can use for this camera in the sun. This viewfinder is actually bigger than the Coolpix, and goes against the whole reason for getting this tiny Coolpix in the first place. So why would anyone get this camera? Ironically, you’d get it for that 18.5mm lens. It’s really, really good. The resolution is simply sensational, and it has virtually no distortion. I sorely miss vibration reduction, however. Coupled with the absence of an optical low-pass filter on the sensor, you’ll probably get sharper shots with this camera than you can achieve with a DX DSLR. There is a manual focus ring at the base of the lens (it’s rotation-speed-sensitive on focusing rate). You can stop down to f/22.0, but resolution is already mostly ruined by f/16.0 because of diffraction. You can focus down to about 20 inches. I haven’t made much notice of vignetting; I adjust it in photo editors if I want more or less of it. If you slide a little switch on the left side of the camera to the “tulip” position, the lens focus is in macro mode, and you can focus down to 4 inches. This same left-side slider switch has an “MF” position for manual focus, which causes a vertical distance scale to pop up on the screen to help you both focus and also advertise that you’re in manual-focus mode. You can press the “+” magnifier button while focusing to zoom in the LCD screen and easily obtain critical manual focus. If you then press “OK”, it goes back to a full-screen view. If you’re a manual-focus type person, this scheme is rather nice. In full manual exposure mode, the rear dial around the 4-way controller controls the aperture, while the top dial controls the shutter. In aperture mode, the top dial takes over control for the aperture. The Coolpix can fit in your (jacket) pocket, and it’s virtually silent as you shoot. The reason you’d shoot with this instead of your cell phone is because of the sensor. This 16MP DX sensor has 4.77 micron pixels, whereas typical cell phone cameras have 1.4 micron pixels. In terms of light-drinking surface area, that means the Coolpix A has 11.6 times as much pixel area as that cell phone. The shutter only goes to 1/2000 second, but for a 28mm-equivalent lens, I suppose that’s plenty fast. You get a maximum of 30 seconds, plus “bulb”. Since this is a mirrorless camera, the focus doesn’t need any calibration. The focus works via contrast-detect; it’s slow, but it’s quite accurate. This also contributes to very sharp photos. It only weighs 10.6 ounces, which actually conspires against it for steady shooting (it has very little inertia). It’s a magnesium and aluminum camera body, although I wouldn’t call it “rugged”. It has a cheesy little vertical bar that they call a “grip”. I’m used to the really good grips on Nikon’s pro and enthusiast cameras, so this camera is very disappointing in that regard. It only accepts a single SD/SDHC/SDXC card. The sensor supports a native ISO range of 100-6400, but please, please stay away from 6400. You can actually crank it up to 25,600 (Hi-2) if you want to emulate the painter Georges Seurat. That LCD display is 3” and 920K dots. The 920K specification sounds pathetic, compared to modern screens, but the view actually looks pretty good. Nikon offered a hot-shoe-mounted optical viewfinder (DF-CP1) that sold for a whopping $450.00 US! I wonder how many of those they sold. It also makes the camera look like something out of the 1950’s. The camera can only shoot at 4 fps continuous; modern cameras really spoil us with speeds that are about double this pace. Time marches on. Its EN-EL20 battery is rated at 230 shots. You can shoot 1080p movies at 24, 25 or 30 fps if you’re interested in video. It does have a stereo microphone and mono speaker. Your cell phone is probably a better choice. The Coolpix A sports the “U1”,”U2” user mode settings, which I will always consider to be vastly superior to the “pro” camera memory banks. I still question if a single Nikon engineer has ever actually taken a photograph. Don’t get me started. If you use built-in flash, this camera has a joke of a pop-up flash that sticks up a little over a quarter of an inch. Amazingly, it doesn’t readily produce the dreaded red-eye. The pop-up flash cannot act as a commander to other flashes; oh, well. You can slip the standard flashes into the hot shoe, such as the SB-600 and SB-700. You can use the cheap Nikon ML-L3 infrared remote to control it, thank goodness. It’s a bummer that the only IR receiver on the camera is on its front; I personally want to use a remote from the rear of the camera about 95% of the time. The Redeeming Feature: Lens Resolution The following charts show what kind of resolution performance you can get out of this lens. These are taken from un-sharpened 14-bit Raw pictures. MTF50 resolution lp/mm f/2.8 The resolution numbers are just astonishing. And this is with the lens wide open. Excellent, except in the corners. MTF50 resolution lp/mm f/4.0 This is nearly as good as I have seen from the best lenses you can get. Just a slight drop-off in a couple of corners. I think that the sagittal-direction central doughnut pattern is due to the lens aspherical element. MTF50 resolution lp/mm f/5.6 Great resolution throughout. MTF50 resolution lp/mm f/8.0 MTF50 resolution lp/mm f/11.0 Diffraction is starting to affect the resolution by f/11, just as you would expect. It’s still extremely good, however. MTF50 resolution lp/mm f/16.0 Diffraction is really starting to kill resolution at f/16. I don’t have the heart to try measuring f/22. MTF contrast plot The following plot was actually measured, and isn’t the usual “theoretical” MTF contrast plot that manufacturers publish. f/2.8 Contrast at 10, 30, 50 lp/mm Lateral Chromatic Aberration Lateral Chromatic Aberration f/2.8 Even wide open, CA is already a “don’t care”. Lateral Chromatic Aberration f/4.0 Lateral Chromatic Aberration f/5.6 Lateral Chromatic Aberration f/8.0 Lateral Chromatic Aberration f/11.0 Lateral Chromatic Aberration f/16.0 Samples Sherman building, built 1857. Washington DC. f/5.6 1/800 ISO 100 Rose Chapel built 1870, Washington DC. f/5.6 1/250 ISO 200 Lincoln life-sized statue by Lincoln’s cottage, Washington DC Washington DC historic house Potato Chip Rock, Poway, CA. It's really that thin. San Diego skyline panorama. Stitched with Lightroom. f/2.8 1/800 ISO 100. Bokeh is decent in most circumstances. Color sketch, in-camera retouch menu option. Slightly cheesy. Summary In terms of attractive features, the Coolpix A has quite underwhelmed me. I think that the D7000 had far more features and flexibility for about the same price. At the same time, the Coolpix is very, very portable. I imagine that Nikon expected photographers to slip this camera into their pockets (which you actually can) to always have gear available. Cell phones really ruined those plans, however. You might think of the Coolpix A as a cell phone without the phone or the apps, which I’m sure is the typical Millennial opinion. You would get this camera for its lens; it won’t disappoint if you happen to like this focal length. The Coolpix A is an interesting mix of cheesy and nice. I think of it as a ‘tourist’ camera. To give credit where it’s due, this camera hasn’t broken down in any way over the years. It is a pretty well-made camera. I was a skeptic of its auto-extending lens (when you turn it on), but it still works like new. When it’s off, there’s no lens to bump and it keeps the front lens surface clean. It’s kind of nice to not worry about a lens cap. I still take this Coolpix A out with me occasionally, when I don't want to lug any "real" camera gear along. My cell phone just doesn't have the satisfying 'feel' of a camera, and it's sensor can't compete with my Coolpix in really dim light. I never thought that I'd hold onto this camera for so many years, but I still don't want to let it go.

Anybody who has followed my site knows what a fan I am of the MTFMapper program. Frans van den Bergh, the author, has expanded his program’s offerings (version 07.29) to now include lateral chromatic aberration (CA) measurement. His free program can be downloaded from here: If you’re interested in axial chromatic aberration, this same program can help you measure that, too. Check out this article What Does Lateral Chromatic Aberration Look Like? Lateral chromatic aberration rears its ugly head The shot above shows typical CA. It’s those purple edges you see mostly in the corners of your photos, especially when you have a dark object against a light background. Notice how those purple edges aren’t the same in the radial/sagittal (think wheel spokes) direction versus the tangential/meridional direction. Most lenses show this CA defect much more in the tangential direction. The colors of CA can look different, depending upon the lens. The new CA measurement feature gives you a pair of measurement plots that contain Red/Green and Blue/Green analysis. Since the camera sensor has a Bayer grid of red, green, and blue pixels, the program takes advantage of this extra information. If you’d like to be able to attach useful numbers to this coloring defect, in order to compare one lens to another, or to compare different aperture settings on the same lens, then this program feature is for you. My absolute worst lens for chromatic aberration: Rokinon 8mm When it comes to CA, a lens that has an embarrassing abundance is my Rokinon 8mm fisheye. As you can see above, it’s much worse in the blue-green region than the red-green region. The plot above shows typical output from this new program feature, where I configured it to measure CA in “microns”. Notice in the chart above that CA isn’t perfectly symmetric about the lens center. Most web sites will just give you a single number for this measurement, but it just isn’t that simple in real life. The plot ‘negative’ measurements certainly don’t mean something like “less than no CA”. Negative measurements just mean the relative shift of one color versus another. With many lenses, this color shift can even transition from negative-to-positive or positive-to-negative. A measurement of zero is still the lens designer’s holy grail. To get the best accuracy in your measurements, be sure to carefully focus the lens and get the chart perfectly flat and parallel to your camera sensor. The shot above was done with a D7100, which has 3.92 micron pixels. The worst measurement here (-12) is equivalent to 12/3.92 or 3.06 pixels. There are multiple units that you can select to measure CA, and those ways are discussed next. I really love the perspective abilities that this fisheye lens gives me (especially after I remove the curved lines in Lightroom) but I don’t love its CA. Select how to measure CA You have the option to measure lateral chromatic aberration in units of microns, pixels, or “percent of radial distance from the lens center”. You will find that different web sites will measure CA in different ways, and this gives you the ability to compare your own results against those web sites. Bear in mind that the “absolute” CA measurement is in microns, since this removes the camera sensor pixel size from consideration. If your goal is to compare different lenses on different cameras, this would be the best choice. You’ll need to remember to enter the correct sensor pixel size in the Preferences dialog, or else your measurements will be garbage. Set the pixel size for micron measurements The units of measurement for lateral chromatic aberration are in microns if you tell it the sensor pixel size. If you don’t select “Line pairs/mm units”, you will get measurements in “pixels” instead of “microns”. Note that the “CA display type” doesn’t have a “microns” option in its list. Preferences to get CA “pixel” measurements Preferences to get “Radial %” measurements A word of caution when using new resolution charts New resolution chart style (with annotations on it) The chart style above may not produce any chromatic aberration plot output unless you deselect the option to use “Line pairs/mm units” in the Preferences dialog. This means you can still get pixel or radial percent output. This limitation will probably be eliminated in the next release of MTFMapper. I notified the author about finding this issue. Addendum 8-17-2020 Frans did fix this issue with the 07.30 version of MTFMapper. The new chart style works just fine, even when using the "Line pairs/mm units". Preferences dialog for new resolution chart style The shot above shows how I specifically avoid Line pairs/mm units when using the ‘new’ resolution chart style. With this setting omitted, my CA plots can be successfully created. The “old” printed chart to use for measurements The same web site where you download the software also has PDF files of various test charts that you can print out. The chart that I used to make the chromatic aberration measurements looks like the one shown above. To get the most reasonable measurement results, you’ll want to print a large chart. My chart is 36 inches X 48 inches. The chart style shown above works for all of the chromatic aberration plot output options. As I already mentioned above, I tried shots using a newer-generation resolution chart (it has an hourglass shape in its center) and the software refused to make chromatic aberration measurements. When I stopped selecting the “Line pairs/mm units” option in Preferences, it started working with this chart style. I’m glad that I still have both kinds of charts. You can just multiply any “pixel” units by the number of microns per pixel of your sensor to convert into microns. For instance, the Nikon D850 has 4.35 microns per pixel, so 2 pixels of chromatic aberration would be (2 * 4.35) or 8.7 microns. To display the chart measurements, click on the “chromatic aberration” option after opening and processing your chart photos. Remember to use “Raw” format photos, because your camera will probably attempt to remove any chromatic aberration if you shoot in “jpeg” format. I suppose that if you took a shot in both Raw and jpeg (with corrections active), you could evaluate just how well your camera can correct for CA. You’ll find that lateral chromatic aberration decreases as you stop down your lens aperture. The MTFMapper program will let you now explore how you can control this lens defect with your lens. Keep in mind that you’ll get different measurements if you shoot with DX versus FX format; FX will look worse than DX on the edges, of course. Rokinon 8mm f/3.5 chart A note of caution: I found out that the use of “stereographic” lens distortion correction (in the Preferences dialog), which should normally be used for my 8mm fisheye, caused problems for this version of MTFMapper. If I left the default distortion correction at piecewise quadratic, it could successfully complete the CA plot. The measurement results for this fisheye lens may be suspect, since I was forced to use a non-optimal distortion correction option. Addendum 8-17-2020 Frans did fix this issue with the 07.30 version of MTFMapper. The "stereographic" lens distortion selection now works for all of the plot types. The vast majority of lenses work just fine in the analysis (I typically use piecewise-quadratic distortion correction). I just thought that I should mention that extreme-perspective specialty lenses might not be handled properly in this program version. I imagine that this shortcoming will be addressed soon. I have the bad habit of stress-testing programs to look for any weaknesses in them. I always try to notify Frans if I notice anything amiss, so that he can analyze and address any issues; Frans has always been extremely responsive. He is already working on this distortion correction issue, which he thinks is associated with the “Bayer channel” selection in the Preferences dialog. Much less chromatic aberration when stopped down If you compare the f/8.0 plot of this Rokinon 8mm with the f/3.5 plot near the top of this article, you can see how much improvement there is when you stop down. Having the CA measurements at different apertures, in addition the standard resolution measurements at those same apertures, you’ve got a lot of good information to determine the optimum aperture to use on a particular camera/lens combination. Conclusion Lateral chromatic aberration measurement is a great addition to the MTFMapper program. Even though photo editors such as Lightroom can mostly remove this lens defect, there is still a slight cost in overall lens resolution to do so. If you’re comparing two lenses that are basically locked in a tie, maybe this CA measurement feature can help to cast the deciding vote. Frans is now accepting PayPal donations at his website http://mtfmapper.blogspot.com/. I encourage you to show Frans your support for his continuing hard work and excellent product. No, he didn’t ask me to mention this. I just think that it's to everybody's benefit if Frans can keep his program current and make it even more powerful.

This is the mirror lens design, called “catadioptric”, which bounces light twice inside the lens. The goal of Nikon lens designers was to make a telephoto lens that was as small and light as possible. This is essentially the same optical design as the Hubble telescope. All designs involve trade-offs, and this design has huge trade-offs. On the plus side, the lens has acceptable sharpness, weighs next to nothing for its focal length, has essentially zero chromatic aberration, and it’s cheap. On the negative side, its fixed aperture is slow, there’s lower contrast, and it has a minor hot spot in the center. With the miracle of digital processing, most optical drawbacks can be minimized or eliminated. One optical issue, however, is this lens’ biggest weakness: doughnut-shaped bokeh. Reflex-Nikkor C 500mm f/8 My lens copy is from 1981. This is from the Nikon era of supreme build quality, so the lens works as well as when it was brand-new. It comes with 39 mm rear filters, including yellow, red, orange, neutral-density, and the L37c UV. A filter is required for the optical design, so I leave the L37c mounted. It comes in a nice hard-leather case, and the filters fit inside the case lid. The lens focuses down to 13 feet, and weighs 2.2 pounds. The real transmission of this f/8 lens is closer to f/11. It comes with a built-in tripod mount, with a button to switch between horizontal and vertical. It’s 3.6 inches in diameter and 5.4 inches long (6 inches with its included screw-in lens hood). The manual focus rotates about 180 degrees, and mine is silky smooth. You need this kind of focus throw, due to its long focal length and narrow depth of focus. The “C” in the lens name indicates that the optics are fully multi-coated. Back in the day, this was a big deal. These lenses presently sell for about $300.00 US in pristine condition. Less than the sales tax on most big telephotos. Like I heard once, it’s dollars to doughnuts. It should go without saying that you need to stick with shutter speeds above 1/500 second. The lens has little inertia, so you need to watch out for vibrations. With modern cameras, ISO is no longer the huge problem that it was in film days, thank goodness. Catadioptric optics with two mirrors to bounce light The optical design shows how it’s great for minimizing physical length, but it also shows how the front mirror blocks a huge amount of light from entering the lens. Mirror lenses are inherently dim. This is one of those “Non-CPU Lens Data” camera setups, which lets you use aperture-priority automatic exposure. I tested this lens on the Nikon D610. Lens Resolution I mentioned above that the lens has acceptable sharpness. Maybe I should have said ‘barely acceptable’. The peak MTF50 values on my D610 were 31.8 lp/mm, where 30 lp/mm is the lower end of acceptable resolution. Corners and edges were typically around 22-27 lp/mm, which is sub-par by today’s standards. You really notice how the center of shots are brighter than the edges; it has a different character than normal vignetting. This is fairly simple to fix in post-processing. I used “live view” at 100% to try to get the best focus on the resolution chart. I leave the shots as un-sharpened raw for the MTFMapper resolution software analysis. Nikon D610 MTF50 results The resolution results are interesting, in that the meridional and sagittal directions look almost like mirror images of each other. Sort of a yin-yang. The peak MTF50 of 31.8 lp/mm equates to 1526 lines per picture height for this camera sensor. Honestly, nearly all modern lens designs will smoke this lens when it comes to resolution. MTF 10-30 Contrast plots You can really see the low-contrast characteristics of the lens in this plot. Very unusual to see the edges seeming to improve compared to the center. Overall, results are underwhelming when compared to modern lenses, but not by a huge amount. Samples Humming bird looking at doughnuts The out-of-focus background has that strange doughnut characteristic. Providing full disclosure here, this is the sharpest out of about a dozen shots I took. Depth of focus is razor thin, and auto-focus was sorely missed. You’ll probably want to leave your camera on “continuous-high” and shoot away as you tweak focus. Auto-focus spoils you rotten. It removes the biggest challenge associated with long lenses. Technology is a wonderful thing. On the other hand, the humbling experience of focusing a big lens yourself can be an interesting challenge. Protea The out-of-focus Protea reminds me of sea anemone. Again, a pretty strange effect. Not a terrible effect, just different. Notice the center is brighter than the edges; many times this is just fine and you can leave it as-is. Conclusion This lens is one of those things that is an acquired taste, which most people will never acquire. If you really, really need to pack a long lens into a small space, then this is about as small as you can get. I have used this lens backpacking; I would never be able to haul my big telephoto on those trips. Long lenses are almost unusable without auto-focus, as far as I’m concerned. When you combine the manual focus with the strange doughnut bokeh, this lens just has too many strikes against it for most uses. It’s easy to see why Nikon and most other lens makers have abandoned this kind of design, auto-focus or not. #review

I will attempt to contain myself during this lens review, but it won’t be easy. This lens is something special. Sigma had a really, really big challenge to try and beat the legendary Nikkor 14-24mm f/2.8 lens. They won, pure and simple. My praise is primarily centered on the resolution measurements I conducted using the MTFMapper program. Simply amazing results. Sigma 14-24 f/2.8 on Nikon D610 Everybody has come to expect Sigma to be simply first-rate with build quality, and they don’t disappoint. I have read that Sigma made this “Art” lens as weather-resistant as their “Sports” series, although I didn’t personally do any tests to back up that claim. The lens comes with a nice zippered semi-soft case and strap, plus a slip-on lens cap. If you look at some other reviews of this lens, such as Lenstip here and LensRentals here, you will find that they both agree with me about this lens. Except mine generally tested better than their copies did! Astonishing. The Sigma 14-24mm f/2.8 DG HSM lens initials mean that it's full-frame (DG) and it uses Sigma's hypersonic motor (HSM) for auto-focus. It omits the "OS" designation, which means the lens doesn't support image stabillization. Since this lens is a member of the Art, Sports, and Contemporary series, it means that the lens can converted by Sigma between Nikon, Canon, Sigma, Sony, and Pentax mounts. I have to admit that this is a tough lens to test. It has such an extreme wide field of view that you have to be super close to the test chart. My resolution results are at a subject distance of 0.7 meters to 1.2 meters, even using my large A0 (4x5 foot) resolution chart. The chart also had to be aligned parallel to the image sensor with incredible precision, or the else measurements were affected. This means that lens resolution at infinity focus can only be inferred. About the only things missing from this lens are optical stabilization (Nikon doesn't, either) and the ability to use front-mounted filters. The Canon version of the lens can be fitted with rear-mounted gels, if you buy their little add-on filter kit. You can also buy third-party adapters for breathtakingly huge front-mounted filters, if you really want them. Sigma also has this massive advantage over Nikon and Canon: their USB dock to program new firmware and focus calibration for both different distances and multiple focal lengths. Customize the calibration at 14, 18, 20, and 24mm with 4 distances each, or 16 total calibrations. You can also get Sigma to convert the lens to a different camera mount, for a fee. To achieve their optical and mechanical quality, Sigma was forced to make this lens large and fairly heavy. I’m used to big lenses, so it’s a non-issue for me. I always use battery grips; the lens balance is just slightly front-heavy on my D610. Lens Specifications Zoom rotation: 80 degrees through the 1.7X zoom range. Focus rotation: 110 degrees Non-removable petal-shaped lens hood. (Sigma can convert it to a shorter round hood for a fee). Fluorine front lens surface coating to repel dirt and water. Angle of view: 114.2 through 84.1 degrees. Close-focus 0.26 meters (6cm working distance) 9 diaphragm blades 17 elements in 11 groups 3 FLD elements, 3 low-dispersion SLD elements, 3 aspherics. Minimum f-stop: 22. Electromagnetic aperture, like the Nikkor “E” lenses. 1150 grams (different weights for different camera mounts) 96 x 132 mm dimensions. Auto-focus is with Sigma’s hypersonic motor (HSM). Manual focus override by just turning the focus ring. The only lens switch is for auto or manual focus (I just leave it parked at “AF”). There’s a distance scale (meters, feet) but no depth-of-field scale. General Impressions I never noticed the delay while focusing, so I’d have to say it’s “fast”. Focus speed becomes a non-issue in an ultra-wide lens, anyway. It’s also quiet, although I’m not a picky cinematographer. I never had any missed focus shots, either. The focus ring felt silky smooth and perfectly damped; you could easily rotate the focus ring with a single finger. You’ll notice that the image magnifies a little bit as you focus closer, but this “focus-breathing” isn’t objectionable. The zoom ring is quite a bit more damped than the focus ring, and the zoom ring is nearest the camera. It’s still a totally smooth rotation, but is a bit challenging to rotate with one finger if you’re in a hurry. The rubber zoom ring has a wider spacing on its ribs compared to the focus ring, for additional tactile feedback about which ring is which. I think it’s just the right distance from the camera body for zooming with my thumb and middle finger while the camera body/grip rests on my palm. I didn’t notice objectionable vignetting in my photos, although it certainly exists; you’ll only tend to notice it at all with a clear blue sky at wide apertures. As long as it doesn’t draw attention to itself, I tend to ignore vignetting. I also didn’t notice any lateral or longitudinal chromatic aberration, although my editing software would rid it automatically, anyway. The pronounced bulbous front lens element is prone to catching the sun in shots; a lens with this many elements is inevitably going to show multiple reflections, which mostly look green. I try to use my hand to cast a shadow and help out the lens shade when possible. You’re bound to find yourself using the “healing brush” after a day of shooting, however, to clean up lines of green reflections. Bokeh isn’t really a useful discussion with a lens this wide. What there is of it looks decent, but not excellent. Consider it to be a non-issue. Distortion The lens has low barrel distortion at 14mm, and virtually none beyond 15mm. It’s a simple type of distortion that can be removed easily in your photo editor. Worst-case 14mm barrel distortion hardly detectable Distortion 14mm corrected in editor 24mm no distortion seen Resolution Tests Like everybody else, I read a few reviews on this lens before I decided to buy it. Those other reviews agreed that the resolution was a bit better than the Nikkor 14-24 f/2.8 lens. My own tests make me think that I got a better copy of the Sigma than most of the other reviewers did; the resolution was striking for a super-wide lens. I use the MTFMapper program to perform resolution and focus tests, which you can get here. I have an article about the MTFMapper use here. All of my resolution tests are done using unsharpened, raw-format from my Nikon D610 (24 MP). I use live view and contrast-detect focus, to eliminate any concerns about focus calibration. I’m showing the best results from about 10 shots at each focal length and aperture tested. I halted each resolution test after stopping down to f/16, because the diffraction effects ruin the resolution beyond this aperture. The lens stops down to f/22, if you really need it. I haven’t seen resolution characteristics quite like these before. The results at shorter focal lengths show a sort of sine wave pattern of sharpness, versus the expected gradual tapering-off as you move away from the lens center. You might want to avoid using a focus point at 6mm and 12mm from the screen center, unless you use live view or stop down the lens to about f/5.6 or beyond. The resolution numbers in the center of this lens are quite astounding. The edges are better than expected, although the meridional versus sagittal results at a few focal lengths show a fairly large separation (astigmatism). I’m guessing that the use of the 3 aspherical lens elements causes the unusual-looking resolution progression as you move from the lens center toward the edge. Seeing the 14mm f/2.8 resolution results, I can’t wait to travel to the mountains and try out some starscapes away from the city lights that I unfortunately have to contend with. 14mm f/2.8 MTF50 lp/mm resolution These results are just remarkable. I show the results separated out into both sagittal and meridional directions across the whole image sensor (Nikon D610). This is a very unusual pattern that I haven’t seen before. Note the subject distance is only 0.71 meters to cover the test chart dimensions of about 4 by 5 feet. I can’t answer how the resolution numbers might change when focused on infinity. The usual MTF contrast plot, but made from real measurements The contrast plot above (14mm f/2.8) shows how lens resolution is usually depicted, except MTF contrast plots from most manufacturers are “theoretical performance” without considering the camera sensor. This plot is from the actual measurements on the camera sensor. A close-up from the middle of the resolution target The shot above shows a portion of the resolution target photo center, although it is overlaid with the edge resolution measurements in “cycles per pixel”. You have to know the sensor pixel size (5.95 microns here) to convert into other resolution units. As noted in the picture, I saw a peak resolution of 65.3 lp/mm. This is the same as 3133 lines per picture height, in the sagittal direction. The meridional direction peak resolution was 63.6 lp/mm or 0.38 cycles per pixel. Test chart corner, 14mm f/2.8 The extreme corner of the resolution chart is shown above. On many lenses, you only see numbers like these in the chart center. Wow. It’s crisp right out to the corners. . 14mm f/4.0 resolution and MTF contrast plot 14mm f/5.6 14mm f/8.0 14mm f/11.0 14mm f/16.0 16mm f/2.8 16mm f/4.0 16mm f/5.6 16mm f/8.0 16mm f/11.0 16mm f/16.0 20mm f/2.8 20mm f/4.0 20mm f/5.6 20mm f/8.0 20mm f/11.0 20mm f/16.0 24mm f/2.8 24mm f/4.0 24mm f/5.6 24mm f/8.0 24mm f/11.0 24mm f/16.0 Coma Tests I use a little laser behind a tiny hole in aluminum foil to substitute as a star. The lens is focused on infinity, and the target is about 15 feet away. The images shown are at the pixel level (100% magnification). All shots are in the extreme corners of the sensor. I included some comparison shots using my Tokina 11-16 f/2.8 lens. It’s considered very good, but you’ll see that the Sigma clearly beats it, even though the Tokina results are on a DX sensor and the Sigma is on an FX sensor. I also included a shot at f/4.0 to compare to f/2.8 results. There’s almost no difference when stopping down, because the Sigma is so good even wide open. The size of the coma looks the same in all corners of the sensor. Only the orientation of the coma changes. Tokina 11-16 coma at 11mm and 16mm reference images Sigma 14mm wide open versus f/4.0 coma Sigma 14mm coma top left and right corners Sigma bottom right corner Summary This lens is strongest at the short focal lengths, which is how I would prefer it to be. I wouldn’t consider it to be “weak” at any focal length, however. The Sigma is a bit of a specialty lens, given its extreme field of view. I’ll bet that architectural photographers make this a favorite for interior shots. Landscapes, to me, are all about emphasizing the foreground; this lens delivers that in spades. As I had already mentioned, I can’t wait to try this lens out for starscapes. You don’t want to have to stop down a lens for star shots, and it doesn’t look like you need to stop down with this lens. The Sigma 14-24mm f/2.8 DG HSM lens is another major statement by Sigma that they're now in the top tier for producing professional-grade lenses. Sample Pictures 14mm 1/60 f/7.1 ISO 125 14mm 1/60 f/9.0 ISO 160 14mm 1/125 f/16 ISO 100 14mm 1/1000 f/5.0 ISO 100 14mm 1/160 f/10.0 ISO 100 24mm 1/800 f/4.0 ISO 100 22mm 1/800 f/4.0 ISO 100 #review

Sigma TC-1401 Teleconverter on their 70-200 f/2.8 Sport lens You can see how tiny the Sigma TC-1401 teleconverter is. It’s only compatible with a few Sigma lenses, so be careful to do some research first to see if it will work for you. It won’t work on Nikkor lenses. Similarly, I don’t think the Nikon teleconverters will work on Sigmas; I haven’t tried it, but they warn against it. I didn't check to see the compatibility combinations with other companies such as Sony or Canon. Being a 1.4X teleconverter, you’ll lose one stop of light; my Sigma 70-200 f/2.8 Sport becomes a 98-280 f/4 lens. Most of my teleconverter tests, by the way, were done using the Sigma 70-200 f/2.8 Sport. This teleconverter is dust and splash-proof, so it has about the same specifications as their “sport” series of lenses. It has 7 elements in 5 groups, so there’s more complexity here than you’d think. It weighs 6.7 ounces, or 190 grams. Sigma claims that you can autofocus at up to f/8, but it autofocused fine on my Sigma 150-600 C at 600mm and f/6.3, which would actually make the final f-stop go to about f/9. I tested this on a Nikon D850; many cameras with less sensitive autofocus will struggle or fail with this combination. At any rate, stick with the “f/8 focus sensors” on your camera. Also, stick with decent light levels if you expect any performance using autofocus on this lens. Some of the lenses compatible with this teleconverter include their 120-300mm f/2.8, 500mm f/4.0, and the 70-200 f/2.8 Sport, 100-400 f/5-6.3, 60-600 Sport, in addition to their 150-600 lenses. Pretty slim pickins. Sigma has many busy bees designing for them, though, so I’d expect a larger selection of compatible lenses in the future. I almost exclusively use this teleconverter on my 70-200mm. There’s not enough of a resolution drop or speed penalty to bother me. I don’t think I’d have the same opinion with a 2X teleconverter, but that’s just me. Lens padded case It comes with a little zippered case and lens front/rear caps. No belt loop or clip on it, unfortunately. Focus Speed I measured the impact on focus speed by setting my 70-200mm lens at 200mm, f/2.8 (which then becomes 280mm f/4.0 with the teleconverter). I set the minimum focus distance (about 4 feet). I then timed how long it took to focus on infinity (using phase-detect of course) under sunny conditions. I measured 0.45 seconds, compared to 0.36 seconds on the same lens without the teleconverter. I used the “High Speed AF” algorithm for this test (programmed via their Sigma USB dock). I used “slow-mo” video at 240 fps to review the focusing action (looking at the focus scale). The TC-1401 teleconverter only slowed the lens focus speed down by about 25%. It was hard to even notice a focus slowdown when using the teleconverter. I had braced for something much worse than this. Caution: I wanted to mention that you have to put the teleconverter onto the lens before you mount it onto the camera, or else autofocus won’t work. You have been notified. Sigma USB Dock Sigma USB dock calibration settings: TC-1401 + 70-200 Use Sigma's Optimization Pro along with their USB Dock to calibrate your lenses in combination with the teleconverter. The calibration settings for the teleconverter shown above are saved separately from the (70-200mm lens) calibration settings. Those clever Sigma engineers know that the lens focus calibration won’t be the same with and without a teleconverter. Your own settings would, of course, be different from these. Bravo, Sigma engineers. Vignetting and Chromatic Aberration The teleconverter reduces the level of vignetting, since you’re using the center of the lens field of view. I didn’t notice enough chromatic aberration to mention with this combination; my editing software would remove any if there was some. Bokeh I don’t think that bokeh was altered enough to notice. It’s quite good on my 70-200, and the teleconverter didn’t mess it up. Distortion I couldn’t see any changes to lens distortion when using the teleconverter, either. Lens Resolution I use the MTFMapper program to perform resolution and focus tests, which you can get here: I have an article about the MTFMapper use here: My resolution chart size is 40” X 56”. Testing with big charts provides a more realistic working distance; the actual resolution target distance is included in each plot below, via the exif data. All of my resolution tests were done using unsharpened, raw-format from my Nikon D850 (45.7 MP) with the Sigma 70-200 f/2.8 Sport. I use live view and contrast-detect focus, to eliminate any concerns about focus calibration. I’m showing the best results from about 10 shots at each focal length and aperture tested. I halted each resolution test after stopping down to f/16, because the diffraction effects ruin the resolution beyond this aperture. Even f/16 starts the resolution plunge, but sometimes you need the depth of field. The f/16.0 setting would be the physical f/11.0 of the lens itself, coupled with the one-stop light loss from the teleconverter. 98mm f/4.0 MTF50 lp/mm resolution The 70mm f/2.8 setting had a center resolution of about 62 lp/mm, or about a 10% resolution loss by adding the teleconverter. The focal length gain is 40%, so this is a win. 98mm f/4.0 MTF contrast plot The sagittal and meridional plots track each other amazingly well here. 98mm f/5.6 MTF50 lp/mm 98mm f/8.0 MTF50 lp/mm 98mm f/11.0 MTF50 lp/mm 98mm f/16.0 MTF50 lp/mm 145mm f/4.0 MTF50 lp/mm 145mm f/5.6 MTF50 lp/mm 145mm f/8.0 MTF50 lp/mm 145mm f/11.0 MTF50 lp/mm 145mm f/16.0 MTF50 lp/mm 195mm f/4.0 MTF50 lp/mm 195mm f/5.6 MTF50 lp/mm 195mm f/8.0 MTF50 lp/mm 195mm f/11.0 MTF50 lp/mm 195mm f/16.0 MTF50 lp/mm 280mm f/4.0 MTF50 lp/mm Without the teleconverter, the lens at 200 mm f/2.8 had an MTF50 lp/mm of about 58 in the center, or about a 22% resolution loss for the 40% focal length gain. 45 lp/mm is still very, very good. This is probably the measurement that people will be most interested in: Wide open at maximum focal length. 280mm f/4.0 MTF Contrast Plot 280mm f/5.6 MTF50 lp/mm 280mm f/8.0 MTF50 lp/mm 280mm f/11.0 MTF50 lp/mm 280mm f/16.0 MTF50 lp/mm Summary You get a 40% focal length increase at the cost of a stop of light and between about a 10% to 20% resolution loss, using Sigma’s TC-1401 teleconverter. You also lose about 25% in focus speed. Again, these numbers were all measured using Sigma’s 70-200mm f/2.8, but you get the idea. I think these modest losses are far outweighed by the gain in focal length. I doubt you’ll even notice the added weight or physical length increase, either. Don't be afraid to shoot with a combination like this wide open. I wouldn’t bother putting this teleconverter on Sigma’s 150-600 lenses, except in special cases. Maybe for 840mm moon shots. Every once in a while, you just can't have too much focal length. I’m very happy with this teleconverter, and it’s always with me when I take the 70-200 anywhere. Sample Shots You won’t notice any sharpness loss. 98mm f/4.0 Closest focus, 280mm f/4.0 It’s the bee’s knees 280mm f/4.0 It doesn’t mess up those out-of-focus backgrounds. . #review

70-200 and Nikon D850, mounted on Arca-Swiss foot The 70-200mm f/2.8 is one of the primary lenses that most professionals and serious amateurs have in their lens arsenals. The Sigma 70-200mm f/2.8 DG OS HSM Sport lens is Sigma's second major version of this lens, and the first of its kind in their "Sports" line. The nomenclature for Sigma initials is as follows: DG means it's full-frame coverage. The OS means it supports optical stabilization. The HSM means that is has Sigma's "hypersonic motor" for autofocus. As is typical for modern Sigma lenses (Contemporary, Art, Sports), they offer a conversion service to change its mount between Nikon, Canon, Sony, Pentax, and Sigma. You can see the switches for focus options, focus-limit, optical stabilization, and custom settings from the top to the bottom in the image above. The round button in front of the switches is one of three programmable auto-focus buttons; the others are on top of and underneath the lens. The focus ring is nearer to the camera body than the zoom ring. The knurled knob near the top-rear of the lens is for locking the tripod collar. Lens padded case General Impressions Sigma revamped an already-good lens and made it better. Or maybe I got an especially good copy. I’m mainly interested in resolution and focus speed for this focal length range, and it delivers both. It also has the legendary weather sealing of the “sports” series of lenses and every characteristic of a fully professional lens, including very good optical stabilization. The exterior lens optical surface has a fluorine-style coating to resist oil, dirt, and water. Sigma’s lens kit also includes a super nice padded case for the lens, a bayonet lens hood with a lock button, and it also comes with a rotate-able tripod collar that has a combination Arca-Swiss (yes!) and conventional ¼-20 tripod thread on the foot. The tripod collar is rock solid. They include hex keys if you want to remove the foot (the collar stays put). I’d recommend you leave the foot on, since it’s at the proper balance point for the lens. The edges are rounded, so it’s comfortable if you use it as a carrying handle with the camera upside-down. The collar has nice click stops at every 90 degrees, after you loosen the knurled knob. As a signature of a pro lens, it includes three programmable AF function buttons (you press whichever one is nearest your finger while zooming). You can use these to initiate focus or lock focus; program them using the Sigma USB dock. There’s also the “Lens focus function buttons” assignment in the camera custom controls. There’s even a programmable focus-limiter switch. Again, use the Sigma USB dock to change its distance behavior. The lens doesn't change its length as you zoom. It's not even remotely close to being parfocal, in case you wondered. This is a big, heavy, tough lens. Sigma’s philosophy is that “it weighs what it weighs”. Their prime motivation is optical results and survivability. It weighs almost exactly 4 pounds and is 8 inches long, sans lens hood. I totally agree with Sigma’s philosophy; don’t sacrifice features or quality just for the sake of weight. I know backpackers will wholeheartedly disagree with this philosophy (I used to be a backpacker myself). I think that the correct mantra is “Resolution, quality, light weight; pick any two”. The barrel is magnesium alloy, and it sports the “E” style aperture which supposedly works better at stopping down while shooting high frame rates. Speaking of the aperture, it has eleven blades, which are rounded (to optimize the bokeh). It uses 82mm diameter front-mounted filters. I’d skip using any UV “protective” filter on this lens; use its deep lens hood for protection instead. You should always be using the lens hood for better quality photos with all telephotos anyway; there's a lot of glass in this lens. It’s already weather-sealed, so filters aren’t needed for that purpose, either. You’ll probably need to lose the lens hood if you try a polarizer, however; it’s too hard to gain access to rotate it. I did all of my testing using the Nikon D850. Lesser cameras may show worse resolution and focus speed measurements. Ironically, this lens didn’t impress me much with the first few test photos I took. Here’s why: the lens needed auto-focus calibration in the worst way. Fortunately, this lens supports the Sigma USB calibration dock. Focus is now perfect at every focal length and at every distance (the D850 AF fine-tune value remains at zero). You can focus calibrate at 4 focal lengths and 4 distances per focal length. Nikon still hasn’t caught on with this feature; they only let you calibrate at a single distance and a single focal length. Blech. In the resolution charts below, the "exif" data shows the AF tune value of "0". That just means the focus tuning is kept inside the lens, so that the camera body can be left at zero. My Sigma USB dock calibration settings I’ll never understand photographers that will pay big bucks for camera gear and never even think about calibrating it. What a shame. While I had the lens on the USB dock, I went ahead and programmed its “custom” switch settings (C1 and C2). I program the C1 switch to use the “Moderate View” optical stabilization algorithm and the “High Speed AF” algorithm. I program the C2 switch to use “Standard AF” algorithm and “Moderate View” stabilization. When the custom switches are both off, then the lens uses “Standard AF” and “Standard View” stabilization. By the way, the stabilization “view” you program has no effect on the actual lens stabilization anti-shake capabilities for the photograph. It’s only a viewfinder preference. At least I couldn’t tell any difference with vibration reduction performance (which seemed excellent to me). It sounds really petty, but my biggest complaint with this lens is the lens cap. It’s very fussy to attach it, particularly if you leave the lens hood on. I’m tempted to get a Nikon cap for it (they fit nicely on it). Focus Speed I measured the focus speed by setting the lens at 200mm, f/2.8 and minimum focus distance (about 4 feet). I then timed how long it took to focus on infinity (using phase-detect of course) under sunny conditions. I measured 0.36 seconds. I used the “High Speed AF” algorithm for this test. I used “slow-mo” video at 240 fps to review the focusing action (looking at the focus scale). I found the focus accuracy and repeatability to be excellent. I see no reason yet to switch to a slower autofocus algorithm. Sigma put their “hypersonic focus motor”, which they call HSM, into this lens. If you’re interested in how fast it focuses, then you’d be foolish not to use their USB dock and program it for the “high speed” focus algorithm. They also have a special “smooth” focus algorithm that’s designed for video use, but it’s the opposite of fast. I found that on another lens (the Sigma 150-600 C) that the "High Speed AF" algorithm is about 20% faster than the "Standard AF" focus algorithm. Teleconverter I also tried using Sigma’s TC-1401 1.4X teleconverter (280mm and f/4.0). The same focus test took 0.45 seconds. The teleconverter only slowed the lens down by 25%. I’ll work on a review of their teleconverter later, but (spoiler alert) I found it to be very good with this lens. I wanted to mention that you have to put the teleconverter onto the lens before you mount it on the camera, or else autofocus won’t work. You have been warned. Also, Nikon teleconverters won’t work on the Sigma. Likewise, you shouldn’t put a Sigma teleconverter onto a Nikkor lens. You have been warned. Twice. Sigma also makes a compatible 2X teleconverter (TC-2001) for this lens; I haven’t tried it. I can go for f/4 but I’d rather not go for f/5.6. Sigma USB dock calibration settings: TC-1401 + 70-200 The calibration settings for the teleconverter shown above are ALSO saved, separately from the 70-200 calibration settings. The Sigma engineers are clever enough to know the lens focus calibration won’t be the same with and without a teleconverter. Your own settings would, of course, be different from these. I’m constantly impressed with those Sigma engineers; it’s almost as if they photograph stuff themselves, as opposed to my impression of Nikon and Canon engineers. Lens Stabilization I don’t have a very scientific method for testing this. I just zoom out to 200mm and try my best to hold the lens steady on a high-contrast target. I got sharp images with 200mm and 1/15 second more than half of the time. This equates to about 4 stops of anti-shake; your own mileage will vary. Their “Mode 1” is for general hand-held stabilization; “Mode 2” is for panning operations. In both modes, be aware that it takes about 1 second to be in full stabilization mode after you begin focus or half-press the shutter. Sigma claims 4 stops of stabilization, so I think they’re honest about what their lens delivers. Everybody is different in how they hold their camera, so I don’t think there will ever be a good measure of this specification. Infrared For those who are interested, this lens doesn’t work well for infrared. It has the dreaded hotspot in the middle of the frame. Vignetting and Chromatic Aberration The following shots are some details from one of my resolution targets. They give you an idea of the worst case (f/2.8) on full frame. Chart center with pure white background, 70mm f/2.8 Chart corner. Background definitely not white. 70mm f/2.8 Chart center, 200mm f/2.8 Chart corner, 200mm f/2.8 There is only the barest hint of chromatic aberration; it’s down in the ignorable region. I couldn’t detect any longitudinal chromatic aberration. Vignetting is what I’d call “medium”. The shots above give you an idea of worst-case corner vignetting (f/2.8). Decide for yourself if this bothers you. You can of course correct for vignetting in your favorite editor. Bokeh I quite like the bokeh, but this is something you can’t really put a number on. They’ve done what they can with the rounded 11-blade aperture. Distortion There’s a small barrel distortion at short focal lengths and really tiny pincushion at the long focal lengths. There’s not enough to bother with, in my opinion. Lens Resolution I found the resolution-versus-focal-length trend to be the same as I have read on other web sites. It’s weakest at 135mm, but that’s not to say it’s “weak”. You’ll see below that the results are generally in the category of very, very good. The meridional (tangent) direction resolution is generally worse across the board compared to the sagittal direction. This is consistent with probably 95% of all lenses. I’m not aware of any other websites that give you resolution separated into meridional and sagittal directions; they just give you “the number”. The two-dimensional plots below demonstrate how to really understand a lens’ resolution characteristics; a single resolution number is basically nonsense. There’s really no such thing as “the edge” or “the corner” resolution; it’s typically changing all along each edge. To me, resolution above about 30 or 35 lp/mm looks good, so this lens looks really, really good. The extra resolution just means that you can crop to your heart’s content. As always, I am only reviewing a single lens copy. I use the MTFMapper program to perform resolution and focus tests, which you can get here. I have an article about the MTFMapper use here. My resolution chart size is 40” X 56”. Big charts provide a more realistic working distance; the actual target distance is included in each plot below. All of my resolution tests are done using un-sharpened, raw-format from my Nikon D850 (45.7 MP). I use live view and contrast-detect focus, to eliminate any concerns about focus calibration. I’m showing the best results from about 10 shots at each focal length and aperture tested. I halted each resolution test after stopping down to f/16, because the diffraction effects ruin the resolution beyond this aperture. Even f/16 starts the resolution plunge, but sometimes you need the depth of field. The lens stops down to f/22, if you really need it. 70mm f/2.8 MTF50 lp/mm resolution These resolution results are first rate. I show the results separated out into both sagittal and meridional directions across the whole FX image sensor (Nikon D850). The center peaks at about an MTF50 of 62 lp/mm or 2962 l/ph. Let me repeat: that’s at f/2.8. The usual 70mm MTF contrast plot, but actual measurements The contrast plot above (70mm f/2.8) shows how lens resolution is usually depicted, except MTF contrast plots from most manufacturers are “theoretical performance” without considering the camera sensor. This plot is from the actual measurements on the camera sensor. You can tell that astigmatism is fairly minimal, since the meridional and sagittal plots track each other pretty well. 70mm f/4.0 MTF50 lp/mm resolution The center peaks at about MTF50 70 lp/mm or 3346 l/ph. 70mm f/5.6 MTF50 lp/mm resolution 70mm f/8.0 MTF50 lp/mm resolution 70mm f/11.0 MTF50 lp/mm resolution 70mm f/16.0 MTF50 lp/mm resolution 102mm f/2.8 MTF50 lp/mm resolution (close enough to 100mm) 102mm f/2.8 MTF contrast 102mm f/4.0 MTF50 lp/mm resolution 102mm f/5.6 MTF50 lp/mm resolution 102mm f/8.0 MTF50 lp/mm resolution 102mm f/11.0 MTF50 lp/mm resolution 102mm f/16.0 MTF50 lp/mm resolution 135mm f/2.8 MTF50 lp/mm resolution 135mm f/2.8 MTF contrast 135mm f/4.0 MTF50 lp/mm resolution 135mm f/5.6 MTF50 lp/mm resolution 135mm f/8.0 MTF50 lp/mm resolution 135mm f/11.0 MTF50 lp/mm resolution 135mm f/16.0 MTF50 lp/mm resolution 200mm f/2.8 MTF50 lp/mm resolution 200mm f/2.8 MTF contrast 200mm f/4.0 MTF50 lp/mm resolution 200mm f/5.6 MTF50 lp/mm resolution 200mm f/8.0 MTF50 lp/mm resolution 200mm f/11.0 MTF50 lp/mm resolution 200mm f/16.0 MTF50 lp/mm resolution Summary This lens is strongest at the short focal lengths, which is typical of just about all zooms. It isn’t, however, “weak” at any focal length. The Sigma 70-200mm f/2.8 DG OS HSM Sport lens is a total winner in my book. The 70-200 acts and feels very professional in all regards. This lens will not disappoint you, provided that you take the time to calibrate its focus. I mean calibrate it by using the Sigma USB dock, where you calibrate multiple focal lengths and distances. While you're at it, program its "High Speed AF" focus algorithm, too. I really love the bokeh that this Sigma provides. I'll bet wedding photographers will snap this lens up. Sample Pictures Bokeh sample. Very smooth and creamy. Distance shot, which needs some cropping Detail from shot above The lens is so good that you can do pretty extreme crops and still get good detail. A good camera sensor doesn't hurt, either. Those eleven rounded aperture blades really help here Details come through edge to edge #review

This document was created to explain in simpler terms how the mtf_mapper_gui.exe program works. The program has two main purposes, (1) to aid camera focus calibration (2) lens resolution measurement. This program and other programs offered at the link below actually do a lot more, but this is what most photographers are interested in. The MTF Mapper program author is Frans van den Bergh. His software and printable test charts are available here: Frans comes across as a scientist-type guy, and his documents can sort of take your breath away. They’re worth a read, though, even if you can’t grok 100% of their contents. More of his writings about image analysis topics can be found here If you like his stuff as much as I do, please let him know! MTF Mapper uses a program called “dcraw” (included in download) that knows most “raw” formats, and is regularly updated for new cameras. The "MTF" refers to Modulation Transfer Function, which refers to how light/dark transitions happen. "MTF50" refers to the highest line frequency (line pairs per millimeter) you can have before 50% of the contrast is lost. Values above about 30 lp/mm are considered pretty good, and anything above 50 lp/mm is outstanding. Resolution Measurement To start out, here’s some typical “Profile” output from his program: Resolution profile plot. Lens MTF50 is about 50 lp/mm To make a profile plot, there are a couple of things that need to be done first: Print out a test chart; print it big, mount it flat, use good heavyweight glossy paper. A0 (about 33” X 47”) is great. "Satin" finish papers work well, too. You may need to change the MTF site test chart file formats from ".svg" (scalable vector graphics) into something your program likes better, such as ".pdf". There is freeware that can do this. Make sure you stick with “raw” mode with your camera, and don’t sharpen the pictures. Photograph the chart (‘contrast detect’, live view mode is recommended) in diffused light. I find that a "+1.0" exposure compensation works best to keep the white background light. Run mtf_mapper_gui.exe File | Open… then pick the picture(s) to analyze Click on “profile” on the right-hand side after the picture analysis finishes. You don’t have to wait for the other pictures to get analyzed. Resolution chart with ‘slanted squares’ provided by Frans The resolution chart has little slanted squares that mostly look like spokes branching out from the chart center. The measurement algorithms work best with edges that have a slant around 5 degrees. The “spoke” structure is ideal to get measurements that can be separated into the sagittal and meridional directions, like most MTF plots are. Unfortunately, the spokes nearest a 45-degree “X” pattern get slightly higher measurements than they should (a few percent higher). For most people, this is a “don’t care”. See below for more information on this, if you’re the “care” type. “MTF50” is a pretty stringent measurement. Most manufacturers give you MTF10 (contrast measure) and MTF30 (sharpness measure). Annotated picture up close The ‘annotated’ picture above shows a zoomed-in view of the measurements for each whole square the program could locate. Good measurements are in green. Marginal measurements are in blue (typically within a degree of 0, 26.565, or 90 degrees). Bad measurements are in yellow. If squares are too small (less than 25 pixels per edge) you get a bad measurement. You don’t have to photograph the whole chart; it finds and measures only whole squares. The chart doesn’t have to fill the viewfinder, but don’t let the chart squares get too small (less than 25 pixels). You’ll probably want to add more exposure than your camera meter indicates; you want a light background with the black squares. If the meridional measurement on a square is different from the sagittal measurement, you have astigmatism. You’ll probably notice that the sides of the squares parallel to each other have measurements that nearly match each other. Don’t get too sloppy here. Bad chart rotation can spoil readings. Diffuse light works better than ‘hard’ light. Use a tripod, remote shutter release or self-timer, and mirror-lockup to avoid vibrations. Bump up ISO if you need to for higher shutter speeds, since higher ISO speeds doesn’t mess up the results nearly as much as blur does. I equate the direction “sagittal” to “spoke”, like spokes on a wheel. The term “meridional” is sometimes called “tangent”, and it’s perpendicular to the “sagittal” direction. Note that different resolution camera sensors will give different MTF50 results; this is normal. Remember to set the "pixel size" in the program 'Preferences' to the correct pixel size! How to convert “cycles per pixel” into other measurements Assume the camera sensor is 3264 X 4928 pixels, or about 15.7mm X 23.6mm. Assume an edge measures 0.27 cycles per pixel. MTF50 lp/mm = cycles_per_pixel * height_pixels / height_mm MTF50 lp/mm = 0.27 * 3264 / 15.7 = 56 lp/mm Line pairs per picture height = Lp/ph = lp/mm * height_mm Lp/ph = 56 * 15.7 = 879 Customize the way mtf_mapper_gui works In Settings | Preferences check the “Line pairs/mm units” if you want these units in the “profile” plot. Verify your camera’s pixel size (microns) in the same Preferences dialog. The Nikon D7000, for instance, has a pixel size of 4.78 microns. A D7100 camera is 3.92 micron pixel size. 2-D Grid Plot of Entire Resolution Chart (D7000) Select the “grid2d” to see the resolution measurements throughout the sensor. The pair of plots separate out Meridional and Sagittal readings. This shows that meridional results are better than sagittal results at this f-stop. I like this chart the best of all the available outputs, since it gives a complete picture of the sensor performance, and it separates the readings to get the best understanding of astigmatism (when sagittal/meridional values are different). There’s a “grid3d” plot if you want it, which is basically taking a 2D plot and viewing it at an angle to get the third dimension. Weird “X” Pattern If you ever notice a sort of “X” pattern that fills most of the 2D plot, but only has a difference range of a few percent, it’s an artifact of the square shape of the camera sensor photo sites (its pixels). Frans has an article about this at the download website. Don’t freak out; your lens doesn’t have some kind of cloverleaf inside it. The “green” sagittal cloverleaf readings above are reading slightly better than they really are; the ’52’ scores are probably nearer to ‘50’. If the chart squares were all locked at a 5-degree tilt, the effect would go away, but then you don’t get to see the sagittal/meridional separation. This is the tradeoff being made. The “Imatest” guys opted for the “only 5-degree squares” and sacrificed providing sagittal/meridional data. Frans says he might someday provide both kinds of charts, so you get to choose which you like better. Focus Calibration Focus Chart provided by Frans showing where to focus For focus tests, print out the focus chart and mount it flat. Photograph it while it’s slanted 45 degrees from your camera, with the left-edge (above) of the chart farthest away from you. There are a few charts to choose from; choose the chart that best matches your lens focal length so that the picture looks most like a rectangle instead of a trapezoid. Only use your “phase detect” autofocus setting (not contrast detect live view) to focus the chart, since the point of this test is to test the phase detect system. Use fairly bright light (typically EV10 or better) to make sure your camera doesn’t have to hunt for focus. Use your center focus sensor, and aim it as shown above in red. Plot of focus chart photo The above results show a slight focus error. The camera focus fine-tune (or the lens fine-tune if it’s a new Sigma lens) will need a (-) adjustment to pull the focus nearer to the camera. You might find it easier to determine the focus error by looking at the "annotated" picture values instead of relying upon the "profile" image. Take several shots before you decide how much to change the focus calibration. Each test will probably be a little different. Photo of Chart. Notice the annotated squares added by mtf_mapper_gui.exe The focus sensor was trained on the center of the big rectangle (trapezoid, actually) vertical right edge. Chart was mounted at 45 degrees, with the left side of the chart farther from the camera. #howto

How it gets information in and out of the lens Sigma sells a USB dock (it looks like a hockey puck) tailored to your lens mount type. It’s cheap enough that you have no excuse not to buy it. The software is free from Sigma. It retrieves the connected lens model, mount type, serial number, firmware version, and customization settings using the Optimization Pro program. It sends firmware updates and any customization settings into non-volatile memory inside the lens. One dock will work with all of your Sigma lenses that support the USB dock (unless you have a mix of Nikon/Canon/Sigma/Pentax/Sony bodies). Older Sigma lenses don’t support this. Optimization Pro Features Firmware updates Update the algorithms for anti-vibration, focus speed, manual focus ‘throw’, and even future added features that haven’t been invented yet (such as focus fine-tune for different apertures on fast lenses? Are you listening, Sigma?) It lets you get any firmware bug fixes without having to send your lens to the factory, and it enables Sigma to alter any communications interface changes, in case Nikon or Canon get cute and try to make a compatibility-breaking change in the future. Tammy (sorry, I mean Tamron) and Tokina users might be out of luck if the lens communications requirements get changed in the future. The lens firmware version is checked when the program gets executed while the lens/dock is connected, so you don’t have to remember to request update checks. Focus Fine Tune For zoom lenses, it can calibrate focus at 4 distances for each of 4 focal lengths (16 total settings). The distances are (1) closest focus (2) near range (3) far range (4) infinity. For prime lenses, you can calibrate focus at 4 distances only. Now, even multiple copies of a lens can be custom-calibrated. Nikon, for instance, can’t tell the difference between two copies of the same lens model, and only knows a single fine tune number to apply. It’s very annoying when you have two camera bodies and you have to mark which lens to assign to which body (I paste the fine-tune value inside each lens cap, along with the lens serial number). Sigma can read its lens serial number electronically, so every lens is unique. Nikon and Canon et al. need to pay attention to details like this. Also note that lower-end cameras with no focus fine-tune can still get tuned lenses if they’re Sigma and use the dock. I think all AF lenses could benefit from this kind of focus fine-tuning intelligence. Real-world zoom optics need different fine-tuning at different focal lengths and different distances, but so far only Sigma seems to acknowledge this problem even exists. The 16 fine-tune settings for my 150-600mm Contemporary zoom Notice the different characteristics of each focal length shown in the “Focus Setting” fine-tune screen. The pathetic single AF shift value that my Nikon D7000 offers would leave the lens functioning very poorly indeed. The available shift range is plus/minus 20. Now I can finally leave my camera AF tune setting on “0”. I suppose a second camera body using this same lens would need a non-zero AF fine-tune value, but at least that would shift all 16 in-lens settings. Note the “Rewriting” button in the dialog box above that should say “Save” instead. Don’t be one of those people that get caught staring at this screen waiting for “Rewriting” to finish. I personally use MTF Mapper software and special focus test charts to evaluate critical focus. MTF Mapper is free; the author is Frans van den Bergh (this guy is absolutely brilliant). His program is available here: . This software lets me get really accurate information to enable me to enter good offset data into the Optimization Pro Focus Setting screen. MTF Mapper can also be used to evaluate lens sharpness, but that’s a topic for another day. It’s an iterative process to estimate the focus offset values to use, reprogram the lens with Optimization Pro, re-photograph the focus test charts, and then re-analyze the photos to see how you did. MTF Mapper uses “dcraw.exe” to decode RAW files, which is frequently updated for new cameras from most vendors. Focus chart analyzed and annotated by MTF Mapper program The above (unsharpened, RAW) photo shows one of the iterations to evaluate focus accuracy. This particular focal length and distance shows a focus error which will require the fine tune value to be decreased to pull the focus more toward the camera. The MTF Mapper web site also provides graphic files that have the test chart images for printing (both focus charts and resolution charts). I mostly use A0 size prints (about 33” X 47”) mounted onto a board; the bigger the chart, the better the results. I also print onto heavy glossy paper. Regular uncoated, lightweight paper sucks for trying to mount it and keep it totally flat. The more diffuse illumination you use when photographing the chart, the better. Also, you want bright light to give your camera focus system the most help (EV 10 or better for most cameras). Charts are of course useless for the “infinity” test shots. With long focal lengths, heat shimmer is a real problem. Maybe something like craters on the moon in cool weather would work best; I have used really distant tree branches or pine needles (600 – 900 feet) with the long focal lengths. Detail from the annotated focus chart created by MTF_Mapper_Gui program Profile view of the focus chart from MTF Mapper program The focus chart large vertical edge is depicted as the vertical blue line above. The smoothed plot of each measured square is depicted in green. Each individual square edge reading is plotted in red (units of MTF50 line pairs/mm). Focus is properly calibrated when the blue line aligns with the green peak. The above plot is from a test of the Sigma 150-600mm Contemporary lens at 600mm at f/6.3 using a Nikon D7000 camera. Note that a few edges actually measure over 40 line pairs per millimeter (and this is considered worst-case sharpness for this lens)! Focus testing was done using AF-C mode (with ‘focus’ button), and it is actually pretty repeatable. This is how this lens is mostly going to be used, so I tested it using the same focus mode. Test-to-test variation was pretty small. I shoot 10 shots at each focal length and distance, and then choose the average focus distance to decide how it is calibrated. By the way, the tested lens (150-600 Contemporary) had zero focus chatter in AF-C. The focus locked and stayed there on the target. This is very un-like my 70-300 Nikkor that chatters constantly, even in good light on high-contrast targets. It’s extremely annoying, and a deal-breaker for me. I read that the new Nikkor 80-400 AF-S VR has the same annoying focus chatter (see the review at photographylife.com). I used to think the chatter was a camera body problem, but now I realize it’s a lens problem. Chatter equals missed focus about half of the time, and focus fine-tune is an exercise in futility. But I digress. Full view of focus chart at 600mm at 19 meters (with annotation text). Note that the focus chart large ‘rectangle’ shown above is actually a trapezoid, to help counteract perspective. The large black ‘rectangle’ edge nearest the photo edge is actually much taller than the large edge in the center of the photo. The little squares are also farther apart vertically at the left edge than the right edge. Use high shutter speeds to eliminate any motion blur side effects; high ISO values have minimal effect on MTF measurements compared to motion blur, so don’t be afraid to push it to get blur-free pictures. I also use my infrared remote unit with mirror lock-up to rid vibrations, in addition to a big-honking tripod. Just remember: “garbage in, garbage out”. It’s worth your while to do careful focus calibration. If you read reviews of a Sigma lens that supports the USB dock but the calibration wasn’t done, then don’t put too much stock in the review in regards to focus accuracy. In this case, the saying goes “nothing in, garbage out”. I don’t see any fundamental reason why Sigma can’t do all of this focus calibration at their factory, but talk is cheap here. Hey, at least they’re giving us the tools to help ourselves. No other manufacturer is even close to this level of sophistication (yet). There a bunch of videos here from a Canadian company that go into detail about using the Sigma software and Sigma topics in general. #howto

The exiftool program lets you extract all of the data out of your photographs into a text file by a simple drag-and-drop operation. This is a really easy way to get at exposure, lens, and camera data, plus much more. You can find out how many total shutter-actuations your camera has done, the “Light Value” (or EV) of the scene, the depth of field, whether you used phase-detect or contrast-detect, etc. What you can’t get is the Nikon lens serial number, although you do get the camera serial number. It’ kind of cool that my Sigma 150-600 Contemporary lens data even gets correctly decoded while on my Nikon. I can give it my RAW files directly, plus a bunch of other formats. You can get this free program here: The author is Phil Harvey. Please thank him! Thank you, Phil. Phil’s software can do many things beyond what I mention here, but here’s how I use it in Windows (Mac OS-X is supported). Select the exiftool.exe file in Windows Explorer Right-mouse click and select Copy and paste into the same directory. Right-mouse click exiftool –Copy.exe and rename it: exiftool(-a -u -g1 -w txt).exe Now, all you have to do is go to a directory with photos and drag/drop a file onto the exiftool(-a -u -g1 -w txt).exe program. You will get a text file (same name as the dropped file, but with a .txt extension) placed right next to the original photograph file. Simple and elegant. Sample Data From Typical Output Text File This program is really, really useful. It's also a real eye opener to know just how extensive the amount of data kept in every photograph really is. Thank you Phil Harvey! #howto

What can you expect from a lens when you change to a higher resolution camera? For crummy lenses, don’t expect improvement. Good lenses, though, are another story. Let’s compare the Nikon D7000 (16 megapixel) against the D7100 (24 megapixel) cameras. The D7000 sensor is 3264 X 4928 pixels, while the D7100 is 4000 X 6000 pixels. Both sensors are the same size, at 15.6 mm X 23.6 mm. Resolution change is evaluated in a linear fashion, so it’s the change in the ratio of either the short or long edge measurement of the sensor, such as 6000/4928 = 1.22, or 22 percent more with the D7100. Doesn’t sound nearly as sexy as 24MP/16MP = 1.5 or 50% bump, does it? If a lens has good enough optics, then you would expect your MTF50 measurements would therefore increase by about 22% by upgrading from the D7000 to the D7100. But wait, there’s more! What about that removal of the OLPF (optical low-pass filter) on the D7100? At the risk of moiré in some pictures (never actually observed by me in any of my pictures yet except for shooting a “Siemen’s star” target) you can squeeze a bit more resolution out of a sensor when you stop fuzzing-out the image by getting rid of that low-pass filter. Low-pass (e.g. don’t pass high-frequency light/dark transitions) filters stop those nasty color patterns you used to see watching TV when some guy would wear a pin-stripe suit. If the pinstripes were spaced at the same interval as the camera sensor elements, it really messes up the image. The OLPF filters work by de-focusing the image a little bit, and therefore ruins those fine details in your carefully-focused picture you paid big bucks to get. You get the lost resolution mostly recovered by using the “un-sharp mask” in your favorite image-processing program. It always seemed a real hoot that “un-sharp” was used to get “sharp”. Another way to get rid of moiré is to use the "moire removal" feature in many modern image-processing programs designed specifically for that task. In any event, moiré is a “don’t care” for most people and most photographs. After that major digression, let’s get back to lens resolution and camera sensors. We’re expecting about 22% improvement in MTF50 measurements, not counting the OLPF filter removal. This assumes the lens resolution isn’t already maxed-out on the D7000. MTF50 results for Sigma 150-600mm lens on D7000. MTF50 results for Sigma 150-600mm lens on D7100. Using the above Sigma lens results, we get a MTF50 high-reading change from 40 to 48, or about 48/40= 1.2 = 20%. On the low end, the change is from 26 to 30, or 30/26=1.15 = 15%. Next, let’s check out my best-resolving lens: MTF50 results for Nikkor 85mm lens on D7000. MTF50 results for Nikkor 85mm lens on D7100. Using the above Nikkor 85mm f/1.4 AF-S lens results at f/4.0, we get an MTF50 high-reading change from 54 to 68, or 68/54 = 1.26 or 26%. On the low end, the change is from 46 to 52, or 52/46 = 1.13 or 13%. Conclusion If you have a pretty good lens, you can expect to get nearly the theoretical maximum resolution change. It’s unclear (no pun intended) the contribution of the OLPF filter removal to overall resolution, but I’m getting around 26% overall (camera sensor plus OLPF removal). The OLPF removal must be at least 4% improvement. Corners aren’t quite as rosy of a scenario, but still a substantial improvement. BTW, don’t abandon the un-sharp mask when post-processing just because you don’t have the OLPF filter. You’ll still see a huge bump in sharpness. #howto