Here I go again. I intend to question authority. This time, I’m going to perform some tests to see just how superior contrast-detect autofocus is at nailing focus, compared to phase-detect. We all know how slow contrast-detect focus is, but the results are totally worth it, right? I have been picking on my nifty-fifty (Nikkor 50mm f/1.8 AF-D) lens lately, and this round of testing maintains that same theme. I did all of these tests using my Nikon D850. Everybody claims that the AF-S focus technology is faster and more accurate than AF-D focus (AF-D requires an in-camera focus motor). If my 50mm AF-D lens can perform okay, then the AF-S lenses (with in-lens focus motors) should perform even better. Cameras designs are always getting better over time, and it may be that “rules” of the past aren’t necessarily true today. Modern sensors that contain “phase-detect” pixels muddy the water even more, since they can eliminate the slowpoke on-sensor focus issue. For each of the following tests, I shot at least 10 pictures at each aperture and focus mode. I am interested in maximums, averages, and ranges of results here. Resolution results are the best indicator of successful focus, so I’m doing an MTF50 resolution analysis as an equivalent to focus analysis. First, calibrate your lens properly It bears mentioning that it’s crucial that you accurately focus-calibrate your lenses; if you don’t, then you might just as well stick with contrast-based focus. Or buy a mirrorless camera (except they don’t work with AF-D lenses!). Get over the idea that lenses are calibrated well enough at the factory. They're not. Out of all of my cameras and lenses, I have only ever had two lens/camera combinations that were factory-calibrated properly. Focus-calibrate with a proper target The picture above shows the kind of target I use to calibrate (phase detect) autofocus. I got this target image from the same site that has the program MTFMapper. The target image tapers from left-to-right, such that perspective distortion makes the image look like both ends of the “trapezoids” appear as perfect rectangles when you rotate the target 45 degrees about the vertical. The web site has a few different images with different amounts of perspective in them. I print and mount different size images, depending upon the lens focal length and the distance to the target that will let me come close to filling the camera’s field of view. The picture shown has its left-hand side further from the camera than its right-hand side. This perspective effect isn’t perfect, and depends upon what lens focal length you’re testing. What is important is that you focus on the vertical edge depicted by the red rectangle as shown. This way, there is no confusion about what edge is used for focus. I always calibrate using these targets to get the best focus accuracy that I can. My MTFMapper program can show me the resolution of each edge in my test photos, so it's easy to see where the sharpest focus lands, versus where the camera tried to focus. Cameras and lenses have some degree of focus variation, which is why I performed multiple tests to get my data. If you have a lens that exhibits spherical aberration, then it will shift focus as you stop it down. This kind of lens problem can potentially defeat you with phase-detect focus (you can only have optimal focus calibration at one aperture). My nifty-fifty has “slight” spherical aberration, so it will be interesting to see if it affects the test results. Contrast-Detect Testing Contrast detect f/1.8 MTF50 resolution The f/1.8 results showed an average MTF50 resolution of 32.7, with a peak of 34 and a range of 2 lp/mm. Contrast detect f/2.0 MTF50 resolution The f/2.0 results showed an average MTF50 resolution of 34.7, with a peak of 35 and a range of 2 lp/mm. Contrast detect f/2.8 MTF50 resolution The f/2.8 results showed an average MTF50 resolution of 47.9, with a peak of 48 and a range of 1 lp/mm. Contrast detect f/4.0 MTF50 resolution The f/4.0 results showed an average MTF50 resolution of 58.9, with a peak of 60 and a range of 2 lp/mm. Contrast detect f/5.6 MTF50 resolution The f/5.6 results showed an average MTF50 resolution of 62.4, with a peak of 64 and a range of 6 lp/mm. Contrast detect f/8.0 MTF50 resolution The f/8.0 results showed an average MTF50 resolution of 59.1, with a peak of 60 and a range of 2 lp/mm. Phase-Detect Testing Phase detect f/1.8 MTF50 resolution The f/1.8 results showed an average MTF50 resolution of 33.5, with a peak of 34 and a range of 3 lp/mm. Phase detect f/2.0 MTF50 resolution The f/2.0 results showed an average MTF50 resolution of 34.7, with a peak of 35 and a range of 1 lp/mm. Phase detect f/2.8 MTF50 resolution The f/2.8 results showed an average MTF50 resolution of 51.1, with a peak of 52 and a range of 1 lp/mm. Phase detect f/4.0 MTF50 resolution The f/4.0 results showed an average MTF50 resolution of 55.3, with a peak of 56 and a range of 1 lp/mm. Phase detect f/5.6 MTF50 resolution The f/5.6 results showed an average MTF50 resolution of 62.3, with a peak of 63 and a range of 1 lp/mm. Phase detect f/8.0 MTF50 resolution The f/8.0 results showed an average MTF50 resolution of 59.0, with a peak of 59 and a range of 0 lp/mm. Summary of Results At the wide apertures, phase detect results are actually superior to contrast detect results. The lens was calibrated at f/1.8, and the lens exhibits a small amount of spherical aberration. It is expected that phase detect will work better at this calibrated aperture, and in fact it does. The repeatability of both focus systems (contrast and phase-detect) seems equivalent. At narrow apertures, the contrast-detect system gives slightly better results. I attribute the better results to the phase-detect system not being able to compensate for the focus shift from spherical aberration. If the lens were calibrated at a narrower aperture, phase-detect results would be better here (at the expense of wide apertures). What I’m not seeing is any overall superiority of contrast-detect focus. I’m not seeing any significant resolution bump and I’m not seeing any tighter focus range, either. As a matter of fact, the largest focus variation (large range value) was found with contrast-detect and not phase-detect! It would be wise to perform an analysis such as this on a lens-by-lens and camera-by-camera basis, but what I’ve seen so far has given me a dose of encouragement. Maybe phase-detect focus has been given a bad rap. Am I going to get a bunch of flak for daring to say out loud that phase-detect can work just as well as contrast-detect?

If you to take a look at many of my articles where I measure lens resolution, it becomes obvious that many lenses are poor at their edges. Numbers can be a bit deceiving, however. The world is, of course, three-dimensional. But all of the lens analysis articles you read present information to you in either one or at most two dimensions. Sure, you’ve probably seen lens resolution plots that are 3-D, but the data shown in them still represents only two-dimensional measurements. Sometimes, a lens has “hidden” resolution. The extra edge resolution is merely bent from the flat plane where the measurements are taken. This is what we call “field curvature”. Older lens designs, particularly in lenses with larger apertures, often suffer from excessive field curvature. Sometimes, even very expensive modern optics have this same problem. For instance, the new Kepler space telescope suffers from this issue, but the designers avoid the loss of edge resolution by making the image sensor curved to exactly match the optical field curvature. For a camera with interchangeable lenses, customizing the shape of the image sensor to match the shape of the lens optimum resolution zone just isn’t practical. The sharpness problem in most cases is minimized by selecting a narrower lens aperture. This solution, however, negates the whole reason for buying your (usually expensive) wide-aperture lens. Lens Resolution 3-D Plots (Meridional upper and Sagittal lower) The lens resolution plots look like 3-dimensional information, but they’re actually only 2-dimensional information taken from the flat camera image sensor. The red colors are higher resolution; the blue colors at the frame sides are lower resolution. Any way you look at it, the edges of the lens results look pretty bad. This (50mm f/1.8) lens may be capable of more resolution on the sides than you think, though. Lens Field Curvature Ray Trace Shown above, the zone of sharp focus for a lens with heavy field curvature doesn’t stay in a plane at the image sensor. Instead, the zone follows a curve (a bowl shape in three dimensions). The curvature might even follow a more complex shape, such as the 3-D plot above, for a multi-element camera lens. How to visualize the shape of the zone of sharp focus If you want to see if your lens has field curvature (as opposed to some other optical defect) that causes unsharp pictures at the edges, what follows are a couple of techniques to do just that. Make sure you shoot test shots with the lens wide open, to see the curvature with maximum effect. The more you stop down a lens, the more the curvature will be hidden, due to the increased depth of focus. Choose a subject that has many, many edges. In my sample shot below, I simply took a picture that is (flat) lawn grass. Lawn grass, Nikkor 50mm f/1.8 Now that I have a shot with lots of little blades (edges) in it, I need a way to enhance those edges. By enhancing the edges of a subject that stretches across the whole field of view, I will be able to visualize the shape and also the depth of what’s in focus. Edge enhancement is built into many photo editor programs. One of the most popular editors that possess edge enhancement features is Photoshop. For this article, though, I’m using Corel Paint Shop Pro, which has many of the same capabilities as Photoshop. Enhanced Edges To make the picture above, I took a lawn grass shot and then selected Effects | Edge Effects | Find All in the editor. There are similar options, such as “Find Vertical” and “Find Horizontal” instead of “Find All”. Choose whichever option best shows the high-contrast edges. Note that I ended up with a “U” shaped band of focus. This shows how the lens field curvature causes the zone of sharp focus to move away from the camera image sensor the farther you move toward the edges of the frame. Instead of just getting out of focus, the focus shifts where it is located. If I were to take a group shot of a bunch of people standing side-by-side, more people would be in focus if they stood along a “U” shape instead of standing in a straight line. For this lens, the people standing on the ends of the line would take a step further away from the camera. It would of course make a lot more sense to just stop down the lens to make sure a group of people has everyone in focus. If you wanted to artistically throw the background out of focus in your group shot, however, you’d have a problem if everyone was lined up straight. Visual Field Curvature with Live View “Focus Peaking” My D850 has Live View focus-peaking. If I turn it on (with “high sensitivity”) and also set my camera to manual focus, I can see the same enhanced edges right on the LCD. I see the characteristic “U” shape when looking at the same lawn grass scene shown above. This would be a realistic technique to determine if everyone in a crowd shot was in focus. That’s preferable to finding out after everybody’s gone home that people at the frame edges are out of focus. Whoops. Same “U” shape field curvature: focus peaking view in D850 Try shifting the focus farther away from the resolution chart To see if my “hidden resolution” theory is correct, I need to move farther from the resolution target and re-shoot it. If in fact the field is curved, then this should make the chart center have decreased resolution and the chart edges should have increased resolution, because the edges have been moved into the zone of where the in-focus areas are located. I won’t touch the lens focus ring or refocus; I’ll just move the camera/lens combination farther away from the chart instead. Target at calibrated focus distance from target: good center, bad edges Focus unchanged, but camera/lens is shifted farther from target You can tell in the charts above that the center resolution got worse as the camera was moved further from the target, since the center was now out of focus. Note, however that the edges/corners significantly improved in resolution. The 50mm lens was focused at 2.5 meters in both cases, but physically moved farther away by 3 inches (about 75mm) without refocusing. Conclusion If I were to make a lens resolution target that was shaped like a dome (or close to the 3-D plot shape at the top of this article), I could make this lens resolution look much more even from edge-to-edge. This would be the only way to really know how much resolution a lens (with field curvature) possesses at the frame edges using a single shot of the test target. I could alternatively take a series of shots of the flat target at different distances, like “focus stacking” does, and piece together the highest-resolving areas from each shot (entirely too much effort). The takeaway from this analysis is that lenses with field curvature don’t have the poor edge resolution that most reviewers quote! The resolution/focus has just curved away from a flat plane. It might be wise to shift the camera phase-detect focus calibration to an intermediate position between the frame center and the edge to balance out the resolution over the whole frame. howto

If you’re curious about how fast a lens can focus, a great way to measure it is to use slow-motion video. I previously used my smartphone video to do this job, but now I can use my Nikon D850. The D850 is capable of 120 fps video in DX crop-mode. This will allow you to time events down to a resolution of .0083 seconds. This is plenty accurate to measure your lens focus speed (lens is mounted on another camera body). D850 setup for slow-motion 120 fps video The overall testing scenario goes as follows. Mount the camera/lens you want to measure on a tripod, and set the focus ring to minimum focus. Make sure the lighting level is set how you want it; dim illumination will of course result in slower-focusing rates. Mount the D850 on another tripod (or hand-held if you’re careful), with its lens focused on the lens focus scale under test. Start the (120 fps) video recording, and then initiate focus on the target camera. Stop recording after the target lens is focused. Make sure the target camera/lens is pointed at something at a long distance, so that its lens will have to move from minimum focus to infinity. I’d recommend the target camera have “AF-ON” programmed onto a button, so you can just press that button to start focus. The recorded video should capture the entire focus sequence, so that you can watch the lens focus scale while it changes from minimum-focus to infinity. The slow-motion video can also capture any focus hesitation or focus “chatter” problems that your un-aided eye cannot detect. Not all lenses have focus scales, of course, so you might have to improvise on tracking what constitutes focus activity. The D850 video doesn’t need to be transferred onto a computer for analysis. You can play back the video recording in-camera, using its multi-selector button. In-camera Video Controls in Video Playback Mode Multi-selector center button: play or resume play after a pause The center button is typically used to play/resume your slow-motion video at the configured frames per second Pause video. Use “forward” or “rewind” while paused for single-frame mode. Rewind the video (back up a frame if “pause” is active) Fast-forward (2X, 4X, 8X, 16X per press) or one-frame advance the paused video Start slow-motion playback if the video is already paused Monitor “beginning of video” indicator (top right of monitor) Last Frame indicator (top right of monitor) Evaluate the video Use the keys shown above to navigate around your video. Locate when the lens distance scale first starts to move in the video. Step through the video to locate when the distance scale reaches the infinity mark and stops moving. Knowing the number of frames (or right-arrow clicks), you can now easily determine how long it took for the lens to focus. At 120 frames per second, that equals 1/120 or 0.0083 seconds per frame. For instance, it takes 30 right-arrow clicks for 0.25 seconds. The math would simply be (30 * .0083) = 0.25 seconds. Review 120 fps video of a stopwatch running on a smartphone In the shot above, I paused the camera video at the frame showing 19.0 seconds, and then clicked the right-arrow on the multi-selector and counted the clicks until the smartphone stopwatch reading was 19.25 seconds. It took 30 clicks, just as expected. It's always good to double-check your work. I used to include a high-resolution timer display in my videos, which shows the elapsed time directly. Using the video navigation controls in the D850 make this additional complexity unnecessary. I did this test on my Sigma 70-200 f/2.8 Sport zoom at 200mm in fairly good light outdoors (the sun was at a low angle), and it took 43 clicks (frames) to go from minimum focus to infinity, or 0.358 seconds. I had previously measured this lens in really bright sunlight (using a stopwatch in the video), and it took 0.36 seconds. Pretty darn close. By the way, this current focus speed test was done using a D500. My previous tests were done using a D850. They’re supposed to have equivalent focusing capability, and this proves that claim to be true. Summary Not many Nikons can manage 120 fps video yet, but the options open up considerably for 60 fps video. Even 1/60 second resolution is pretty good for measuring focus speed, although you might miss some nuances involving focus hunting or focus chatter. Other camera models probably differ in how to review in-camera video, but the discussion above will hopefully give you enough detail to enable you to try it yourself on whatever camera you're using. You may have to transfer the video to a computer and analyze it there, if your camera doesn't include the necessary controls to review it in-camera. This in-camera frame-counting technique makes it really simple to determine focus speed. You could, of course time anything you want using this same technique. Happy testing. #howto

The Hoya Pro ND1000 is a 10-stop neutral density filter. If you like those shots with rivers that look like mist, this is what you use to make them. Ocean breakers that transform into blankets of fog become possible with this filter. If you need to reduce crowds around popular landmarks, this filter is just the ticket. Hoya ProND1000 filter There are many characteristics of extremely dark ND filters that are difficult for manufacturers to get right. Many ND filters suffer from color shift, usually toward pink or orange. Other filters play havoc with lens resolution. Some filters have poor anti-reflection coatings that cause ghost images. Neutral density filters that avoid all of these pitfalls can get quite expensive. I purchased an 82mm diameter filter, so it fits the largest lenses I want to use it with. For my smaller lenses, I have step-up rings to use this filter for anything down to 52mm. Step-up rings are really inexpensive and an ideal way to spread the cost of a single expensive filter over several lenses. I don’t mean to imply that this is the most expensive neutral density filter, but it’s not the cheapest, either. What follows is how I evaluated this filter manufacturer’s claims. I own a couple of other Hoya filters, and I haven’t been disappointed. Auto Focus Impact Can a camera still focus with a 10-stop filter on the lens? It’s a real pain to have to remove a filter to focus a lens, so of course I tested auto-focus. I used my D850 for testing, which can focus down to EV -4. Typical outdoor lighting with a low-angle sun is around EV +10. Since EV increments are in full stops, this means that a 10-stop filter will result in an EV around 0, or 4 stops brighter than the D850’s lower limit. Focus is no problem. Subject Framing without Removing the Filter? Yes, under most lighting conditions, you can still frame the subject without having to take the filter off of your lens. The trick is to switch to ‘live view’ mode and use your LCD screen if your optical viewfinder is too dark. In bright light, the optical viewfinder may be barely sufficient for framing. Viewfinder Eyepiece Cover Please remember to cover that viewfinder eyepiece. Long exposures will cause eyepiece light leaks to ruin your shots. If you’re lucky enough to have an eyepiece shutter on your camera, this is the reason for its existence. Long Exposure Noise Reduction You might start finding excessive bright pixels in your shots with really long exposures. Remember to turn on ‘long exposure noise reduction’ to get rid of those speckles. It will take twice as long, but it may be worth it compared to the amount of time wasted post-processing trying to eliminate them at your computer. Color Shift Analysis I’ll use a grey card to evaluate the color fidelity of the Pro ND1000 filter. For a completely neutral photo, the RGB peaks on a histogram should perfectly overlap. I made a white balance preset with no filter, using a grey card. After shooting the grey card, I then mounted the ND filter and re-shot the grey card using the same white balance preset. The only difference should be the longer exposure with the filter. Grey card with no filter preset white balance The shot above is a grey card using a preset white balance measured with the card itself. Grey card with ND filter, same white balance The shot above is using the Hoya ND filter, with the same white balance as the no-filter preset white balance. It’s a hair different from the no-filter shot, but still quite neutral. The same grey card shot indicates that the density across the filter seems even as well. Illumination characteristics seem the same in the shots with and without the filter. Histogram of grey card with no filter The shot above is the histogram with the white balance measured right off of the grey card without any filter. I used the white balance as-recorded from the raw file. Histogram of grey card using Hoya ND filter The shot above is the histogram using the Hoya Pro ND 1000 filter and the same white balance created from the “no filter” shot. The color transmission isn’t identical to ‘no filter’, but it’s reasonably close. Resolution Analysis A good filter shouldn’t cause any significant change in lens resolution. Physics being real, all filters will have some impact on your lens, but that doesn’t mean that it has to be objectionable or even noticeable. I’ll use the MTFMapper program and a large resolution chart to see how much degradation in lens sharpness this filter causes. Sigma 70-200 at 70mm f/4 MTF50 without filter Sigma 70-200 at 70mm f/4 MTF50 with ND filter Comparing the lens resolution results above (on a Nikon D850), there isn’t enough change to be able to visually tell the difference when using the filter. The MTF50 numbers show the barest hint of a resolution decrease with the filter. Physical Light Reduction It may seem silly to have to verify such a thing, but does the Hoya Pro ND1000 filter really cut the light level by 10 stops? I’m notoriously skeptical about claims, and just because it’s advertised as 10-stop, that doesn’t make it so. A quick way to evaluate photos is via the “Exif Tool”. I took a pair of shots using auto-exposure in sunlight. The exif data indicated the no-filter shot was E.V. 10.3 and the Hoya ND filter shot was E.V. 0.3, so the filter is exactly 10 stops after all. I suppose you could stack this filter with a polarizer or another ND filter if you need yet more light reduction, but 10 stops is enough for most situations. Filter Thickness and Vignetting This filter is fairly thick. It’s about as thick as a typical polarizer. Its (metal) mount is 2.0mm thick (not including threads), and happens to be exactly as thick as my Marumi DHG Super Circular Polarizer. This can cause some vignetting on super-wide lenses, so you may have to crop slightly if your lens only works with “thin” filters. Speaking of threads, this filter screws on and off very smoothly; the threads are precision. I also noticed that it has about a whole extra thread compared to most filters, which makes it very stable when attached. Summary The Hoya Pro ND 1000 filter can transform mundane shots into something magical, given the right subject (and given a tripod). Wind is your enemy; you might consider a shot with and without the filter to have options. I can totally recommend the Pro ND 1000. I wish its mount was a bit thinner, but keep in mind that this filter has to contain enough volume of dark glass to stop a serious amount of light. For photographers who do landscapes or architecture, a strong neutral density filter should be a standard part of their gear. And, once again, don’t forget that tripod. Samples Exposure: 13s f/16 ISO 64 in the sun I confess to using a bit of HDR to make this shot a little more dramatic. It’s the misty water that makes the shot, though. You just couldn’t do something like this without a really dark ND filter. You don’t necessarily want the longest possible exposure time for water; try a few different exposures to give yourself a selection. Fountain of mist Exposure: 30s f/9.0 ISO 32. Yes, my D850 “Lo” can go down to ISO 32. I used my Tokina 11-16 DX at 16mm. The Hoya needed a step-up ring to fit my 82mm filter onto my 77mm diameter Tokina. I had to crop a bit, because this combination causes some dark frame corners on my FX camera. Luckily, the cloud movement was minimal and the sky retains good texture and depth. Ghosts around a pool Exposure: 177s f/10.0 ISO 32. The outrageously long exposure didn’t totally get rid of the crowd around the pool, but it did make about 95% of them disappear. The heavy clouds combined with the ND filter allowed this long exposure time. A light breeze caused many palm fronds to smear; oh, well. The clouds unfortunately moved too much in this long exposure and became featureless. This shot then demonstrates the downside of wind during a long exposure. #review

Lenses don’t focus all colors of light the same way. When a lens gets its focus calibrated on a particular camera, there are a lot of compromises taking place. If a lens has longitudinal (axial) chromatic aberrations, then it focuses different colors of light at different distances from the sensor. I made an article on the topic here: When you perform lens focus calibration, there’s a good chance that the calibration is biased toward a particular color. Where you might notice this bias more is when you’re shooting under different lighting conditions. Shots might look a bit fuzzy, even when you’re certain that you nailed calibration. I wanted to show you a way to measure the magnitude of the color/focus error on resolution. I’m using my usual resolution measurement software: MTFMapper. I picked my little nifty-fifty for these tests (Nikkor 50mm f/1.8 AF-D). This is a cheap, but sharp lens. It’s not without its share of flaws, however. One of those flaws is axial chromatic aberration. Normal MTF50 resolution plot The MTF50 resolution plot above shows what “all” sensor Bayer color channels combined provide. The peak resolution is about 34 lp/mm. This lens is showing its age in many ways, particularly in corner resolution. To be fair, the lens was shot wide open; it looks much better when stopped down. Give this lens credit, though; it's dirt cheap. Now, let’s explore what happens when we isolate sensor color channels. Sensor channel color selection in MTFMapper For the following MTF50 resolution plots, I changed from the default “none” Bayer channel selection to explore what red, green, and blue will produce. Red channel MTF50 Green channel MTF50 Blue channel MTF50 All of the plots shown above come from the same single photograph. The peak resolution ranges from 30 lp/mm for the blue channel to 34 lp/mm for red, and finally 37 lp/mm for green. If you were to photograph something with a lot of blue in it, you might end up thinking that you slightly missed focus. The resolution drops 19 percent from what the green channel sees. Summary It’s unfortunate that nobody seems to mention axial chromatic aberration specifications or measurements when reviewing lenses. This lens issue can have a very large effect on resolution. As always, life is complicated.

This lens harkens back to the early era of Nikon zoom lenses, when everyone was still using 35mm film. It was manufactured from 1989 through 1999. Your Nikon camera needs to have the in-camera focus motor to use this lens; I performed all of the lens tests using my D850. This is a push-pull kind of zoom, which has long since gone out of favor with photographers. At least you don’t have to worry about which direction to twist a zoom ring. If you want to use manual focus, you have to switch the camera focus switch to “manual”. The lens uses 62mm filters, and the filters (plus the end of the lens) unfortunately rotate while focusing. There’s a focus-limit switch, and I’d recommend that you use it. Try to avoid the “full” focus range setting; focusing through the full range is dog slow. The lens has 13 elements in 11 groups. The lens weighs 850 grams. To me, it feels pretty light. It uses the HN-24 screw-in lens hood, although I got a cheap rubber lens hood for it that works just fine. The lens is about 6.6 inches long un-zoomed. The 9-blade aperture can be stopped down to f/32.0 at 75mm and f/40.0 at 300mm. This lens has the old-style full aperture ring with click-stops, but you lock it at the minimum aperture on modern cameras for auto-exposure. The lens barrel is all metal, and it operates smooth as silk. Nikon really went all-out with mechanical tolerances during this era, and its functionality hasn’t degraded at all over the years. There’s no “wiggle” to be found in this lens. It has, of course, a metal lens mount, but there’s no rubber weather seal or any other sealing. The 75-300 has a non-removable tripod collar that doesn’t have any click stops in it. It’s quite solid, although it’s narrower than today’s tripod collars. The lens isn’t heavy enough to make a tripod collar mandatory, but it does help the balance. The collar tripod foot is quite small; I think it should be a bit larger to make it more stable on tripod heads that have plastic or rubber pads on them. This lens predates vibration reduction, and you really notice its absence at 300mm. It’s easy to get spoiled with modern technology. I have to admit that I was anticipating doing little else besides making fun of how poor the sharpness of this lens is. I didn’t give Nikon enough credit, though. If you’re willing to close the aperture down by only about a half-stop, this lens has very good resolution (at least at the shorter focal lengths). The focus distance data (exif data) saved in the photos is garbage. It’s not a “D” lens, so there’s no distance data. It focuses from about 5 feet (1.5m) to infinity. The “macro” range (marked in red on the lens barrel) goes from 5 feet to about 10 feet (3m). The focus “limit” switch keeps the lens inside either of these ranges, depending upon what distance the focus is at when you set the “limit” switch. At the macro setting, you can get down to a magnification of about 1:3.8, which is quite good for a telephoto. Speaking of focus, don’t bother using this lens unless your camera has focus fine-tune calibration or you use live view. This lens desperately requires focus fine-tune calibration or else the results are terrible. Also note that focus calibration changes wildly from short to long focal lengths. Nikon’s mirrorless cameras don’t have in-camera focus motors, so they are of no use here, either. The mirrorless cameras require manual focus with this lens, and also require the FTZ (Fmount to Z mount) adapter. I didn’t notice any distortion in my photographs at any focal length. I didn’t notice enough vignetting to bother fixing it in my photo editor, either. Shots at the end of the article show the extent of vignetting and distortion. There didn’t seem to be much chromatic aberration, which surprised me. I really only noticed it at longer focal lengths with wide apertures. Subjects like small tree branches against the sky are where you see this purple fringing; see the photos at the end of this article. 75-300 lens at 300mm zoom on Nikon D850 The shot above shows the manual-focus ring near the front of the lens. Note the fairly skinny tripod collar and its tiny foot. There’s no wiggle in this lens or collar, though. The rear of the lens has the full-blown aperture ring. Lens at 200mm Focus scale and limit switch up close Note that there is a white infrared focus-shift dot at both 75mm and 135mm just to the left of the visible-light infinity mark. The limit switch (set at the “limit” position) will keep the lens outside of its macro range as shown above. The macro range (5 feet to 10 feet) is the red stripe on the right. Autofocus Speed and Focus Calibration This lens’ autofocus is pretty slow, or reasonably quick; let me explain this awkward statement. After about 30 seconds of focusing frustration, I slid the focus limit switch from “Full” to the “Limit” position; there was a world of difference in speed. With this switch in “Limit”, it would focus from the regular (about 10 feet) near-distance limit to infinity in 0.415 seconds at 75mm. Using the full focus range, it took 0.933 seconds at 75mm (it feels like an eternity). Using the “Limit” switch position at 300mm, it took 0.433 seconds. Leaving the switch in the “Limit” position, focus was pleasantly responsive. I did the testing in good light; my D850 and D500 cameras got the same focus speed results. Lesser cameras are probably a bit slower than this. The first thing I always do with a lens is to focus-calibrate it. An out-of-focus shot is a useless shot. I found out right away that at 75mm, the focus fine-tune setting (-10 on my D850) was nowhere close to what was needed at 300mm. I determined that 300mm needs a fine-tune setting of +10 on the same camera. Major disappointment. Nikon, unlike Sigma, has no way to cope with a focus calibration problem like this other than to tell you to buy one of their mirrorless cameras – oh wait, their mirrorless cameras don’t support screw-drive lenses! I always write the fine-tune calibration settings data on the inside of the lens cap on a sticker (per-camera); it’s too hard to memorize this stuff. If I don’t remember to reprogram the appropriate calibration setting when I zoom in or out, picture sharpness suffers. Chromatic Aberration Worst case chromatic aberration These shots show how bad it can get with lateral chromatic aberration in the corner of the frame (100% magnification). The left-hand f/10.0 shot shows how much it gets improved by stopping down. As the labels indicate, this is at 300mm and the right-hand shot is wide-open f/5.6. The full shots are shown down below; this was taken from about 220 yards away. Given the extreme distance of this shot, I think the lens resolution in the corner of the frame is really remarkable. Infrared Since Nikon added the IR focus-shift white dots on their focus scale, I thought I’d give the infrared capabilities a little test. I used an 850nm IR filter. I found that the focus shift indicators to not be very accurate. I actually needed to shift the distance scale marker more to the left (closer distance) by an additional 3mm beyond the white dot at 75mm zoom. I was impressed by the very minimal hotspot in the middle of the shot (it was only brighter by about 0.3 stops). The vast majority of modern lenses are terrible at infrared, and zooms are the worst. 850nm IR 75mm f/8.0 Resolution I do resolution testing with un-sharpened raw-format pictures. My resolution target is 4 feet by 5 feet, to enable me to be at realistic shooting distances. All tests were done using my Nikon D850 (45.7 MP). I used the MTFMapper program to evaluate the results. I used contrast-detect focus to side-step using focus calibration. As I mentioned above, the phase-detect calibration is all over the place; it depends upon the focal length. I have noticed that this lens prefers distance shots over close-range, especially from 200mm to 300mm. My resolution target (at about 40 feet with 300mm) leaves you with the impression that the lens is worse than it is; some sample distance shots at the end of this article give you a better idea of its sharpness. The resolution measurements are in units of “MTF50 lp/mm”. To convert these units into “lines per picture height”, just multiply by the result by (23.9 * 2.0). For instance, an MTF50 of 40.0 lp/mm is (40*23.9*2) = 1912 lines/ph. The D850 sensor is 23.9mm tall. MTF50 lp/mm 75mm f/4.5 Even at a wide open aperture, 75mm is decent. MTF Contrast Plot: 75mm f/4.5 Test chart center detail with MTF50 lp/mm values shown on edges Test chart corner detail. MTF50 lp/mm values shown on edges MTF50 lp/mm 75mm f/5.6 There’s a huge increase in resolution by stopping down just a little from wide open. MTF50 lp/mm 75mm f/8.0 This is the sweet spot for 75mm. It’s only a tiny bit better than f/5.6, though. MTF50 lp/mm 75mm f/11.0 MTF50 lp/mm 75mm f/16.0 MTF50 lp/mm 135mm f/5.0 MTF Contrast Plot: 135mm f/5.0 MTF50 lp/mm 135mm f/5.6 MTF50 lp/mm 135mm f/8.0 MTF50 lp/mm 135mm f/11.0 MTF50 lp/mm 135mm f/16.0 MTF50 lp/mm 200mm f/5.3 Yikes! Avoid 200mm f/5.3 at all costs. MTF Contrast Plot: 200mm f/5.3 MTF50 lp/mm 200mm f/5.6 Stopping down just a tiny bit from wide open really helps sharpness. MTF50 lp/mm 200mm f/8.0 This is probably the sweet spot for 200mm. MTF50 lp/mm 200mm f/11.0 MTF50 lp/mm 200mm f/16.0 MTF50 lp/mm 300mm f/5.6 MTF Contrast Plot: 300mm f/5.6 MTF50 lp/mm 300mm f/8.0 MTF50 lp/mm 300mm f/11.0 MTF50 lp/mm 300mm f/16.0 This is definitely the best aperture for 300mm, even though lens diffraction is setting in just a bit. Sample Pictures 300mm f/5.6 Macro, 5 feet Believe it or not, this is considered one of the worst settings for this lens. I think the lens did quite well. The background melts away beautifully. This would be an ideal distance to avoid disturbing a butterfly, compared to regular macro lenses. 75mm f/5.6 I don’t see any vignetting here, and the palm fronds are razor sharp. 75mm f/5.6 I don’t see any linear distortion 300mm f/5.6 I don’t see distortion here, either 300mm f/10.0 Very sharp distant branches at about 220 yards 300mm f/5.6 has chromatic aberration & vignetting, but pretty sharp 300mm f/8.0 Decent sharpness Conclusion Before I started testing this lens, I figured there would be little to do besides mock it and talk about how old lenses really show their age. This has been a humbling experience. The mechanical and optical quality is really quite good. By far, my biggest complaint about this lens is the annoying shift in focus calibration as you zoom it. Mirrorless cameras can’t cure it, since they can’t use the screw-drive lenses. It’s easy to imagine many photographers thought it was a generally un-sharp lens, not realizing how to compensate for it. When this lens was introduced, autofocus calibration fine-tune hadn’t even been invented yet. Chromatic aberration at longer focal lengths can be seen in high-contrast scenes, but stopping down greatly improves it. Although my modern Sigma telephoto zooms smoke this lens, I can honestly say that the AF Nikkor 75-300 f/4.5-5.6 takes really beautiful photographs. If you think about the primitive state of computers and software back when this lens got designed, it’s quite amazing what those Japanese engineers were able to accomplish. They should be rightfully proud. Nikon sold this lens for a whole decade; now I can see why it sold for so long.

If you buy Sigma’s USB dock to reprogram their lenses, it gives you the option to not only update their lens focus firmware, but also which focus algorithm(s) to choose. It’s almost like buying a new lens. If you have never programmed your Sigma lens using their dock, then your only focus choice is “Standard AF”. You get to choose among three different “AF Speed Settings” if you program their lens via the “Sigma Optimization Pro” program. The choices are “Fast AF Priority”, “Standard AF”, or “Smooth AF Priority”. The Sigma lenses that support the customization have a “C1” and a “C2” switch to change modes. It’s possible to have three different settings collections, using the custom switch set to “Off”, “C1”, or “C2”. If it’s set to “Off”, then you’d get their “Standard AF” (in addition to their default optical stabilization view mode). You could set the C1/C2 switches to the same or different algorithms. The “Smooth AF Priority” is geared towards video shooters, and the focus is slow. I’m not a video shooter, so I don’t use this customization. If you’re a videographer, however, this option might be the deciding factor in buying a lens. The “Standard AF” is medium-speed, but purportedly more accurate for focus accuracy and repeatability than a quicker focus. I have my “C2” switch set to this focus mode. The “Fast AF Priority” is their quickest focus mode, and it’s how I set my “C1” switch now. I didn’t leave it programmed this way when I first got Sigma’s programming dock, however. When I first got my Sigma 150-600 Contemporary, I found that my “Fast” setting wasn’t reliable, and I was forced to leave the lens on “Standard AF” to get accurate and repeatable focus. After Sigma updated their lens firmware, I discovered that their focus was made faster AND more accurate, in both the “Standard AF” and “Fast AF Priority” modes. The “Fast” mode was now so accurate and repeatable, that I use it exclusively. I left my C2 switch with the standard AF option just in case, but I’ve never needed it. I did some focus speed testing experiments, to see how much different their “Standard” and “Fast” modes were. I used my “Super Slow Mo” video setting on my cell phone and a very accurate timer to evaluate focus timing. I performed the tests using my Nikon D500 camera, to get an idea what a “pro-level” camera could do with this lens. Sigma Optimization Pro Focus Programming Example You can see what the Sigma programming dialog looks like above. They have other dialogs for programming optical stabilization, focus distance ranges, and focus calibration. It gives you feedback about how it’s already programmed, in case you forgot. I leave little notes taped onto the inside of my lens cap about how each switch is programmed. Use a timer and super-slow-mo video to track focus timing It was pretty straightforward to take some video (240 frames per second) to accurately time focus. I set my Sigma lens on minimum focus (about 9 feet and 600mm zoom). I used a big rubber band to attach a cell phone with a timer application onto the lens, near the focus distance window. I’d start the timer, then start video recording, and then finally press the “AF ON” button to focus. I could review the recorded video right on the phone, and swipe from frame-to-frame while reviewing the footage. I could easily see as the timer changed by hundredths of a second in the video. I used a pair of cell phones here, since I needed to make a video of the timer display next to the lens focus-distance scale display. I made sure that the big rubber band wasn’t in a location on the lens that would interfere with the lens focus operation. I would simply start the video recording and then press the “AF ON” button to focus on a high-contrast, distant target. I could review the video frame-by-frame (with a finger swipe) to see the timer value when the lens distance scale started moving, until it reached the infinity mark. I repeated the procedures to convince myself that the test was repeatable (it was). I had to shade the phone screen and lens focus scale to record their images well enough in the video. The timer application I used records down to 1/100th second. I made a few videos at both the “Fast AF Priority” (C1 switch) setting and then again at the “Standard AF” (C2 switch) setting. The timing was remarkably repeatable from test-to-test, so I have good confidence in the results. I skipped trying the “Smooth” auto-focus algorithm, since I am only interested in speedy focus. I used my Nikon D500 for this test, since it has the fastest auto-focus of my cameras, due to its Expeed 5 processor. I didn’t want a slow-focusing camera to affect my lens speed measurements. The “Standard AF” algorithm timing was 0.55 seconds to go from minimum focus to infinity. The “Fast AF Priority” algorithm timing was 0.44 seconds for the same focus range in the same (good) outdoor lighting. In the real world, nobody actually goes from minimum distance to infinity in a shot (unless they’re a rank amateur). More likely, focus will be changing by only several feet shot-to-shot. Using the lens like this, the focus time is more like a few hundredths of a second, as witnessed in the video footage, changing from about 30 feet to about 40 feet. It is slower, of course, when the lens has to switch focus directions. Once you have your recording setup, you can now explore different focusing scenarios that apply to your own style of shooting. Focus speed timing only makes sense if it reflects how you’d actually use it. Different lenses with different minimum focus distances and different focal lengths can’t be directly compared. You also need a sufficient level of illumination to compare different lens/camera combinations. I have read an article about someone comparing both the Sigma Contemporary 150-600 against the Sigma Sports 150-600. The Sports version has larger-diameter (and much heavier) lens elements in it, and actually focuses SLOWER than the Contemporary version. The focus motor is purportedly the same in both lens versions. I don’t have the Sports version to test, but these reported results make sense. Keep in mind that not all lens elements are necessarily in motion while focusing, and clever lens designers don’t move more glass than they have to. Don’t forget to use the focus-limit switch on your lens, if it’s available. It can make an enormous difference in focus acquisition speed if your subject movements are predictable enough. The focus limit range is yet another programmable setting with Sigma lenses. The bottom line is that the Sigma focus algorithm speed difference is 20 percent between Standard and Fast. I can’t tell any differences in accuracy between them. Without the programming dock, this speed improvement wouldn’t be available. I wanted you to know how I performed the speed timing measurements so that you can do these tests yourself and evaluate your own equipment. You don’t need elaborate equipment; just modern cell phone technology. #howto

Flash FP Mode This article discusses the Nikon FP flash mode, which is often derided by photographers as ‘beneath contempt’. That’s not my opinion. What is it? FP mode causes your (external) flash to emit a bunch of rapid light bursts instead of one big one. These rapid bursts keep the xenon in your flash continuously energized, so the light output stays at an almost-constant level. The upside to this is that you can use a shutter speed like 1/4000 and still use flash. BTW, “FP” is short for “focal plane”, and is perfectly descriptive to nobody outside of Sendai Japan. Think “flash bulb” for those of you born during the Pleistocene epoch. What is it good for? FP mode enables you to use high shutter speeds in conjunction with your flash, so you can do things like fill in shadows outdoors in sunlight. You can fill in those terrible dark blobs under the eyes and nose, and you can get that sparkle back in the eyes. You can use those large apertures you paid for while outdoors, and still get fill-in flash. FP mode isn’t something you would want indoors; regular flash mode will work better there. It’s really just available so you can get beyond the “sync speed” of the shutter while outside. It's true that you can use something like "D-Lighting" while postprocessing the picture to fill in those shadows, but this is really second-best to getting it right in the beginning. You don't want to add shadow noise when there's any easy (better) option. If you're too far away from your subject you may have no choice, but your flash can have a positive effect from farther away than you might think. There is still no such thing as a free lunch. The light output from your flash will be less (about 2 1/3 stops). And you have to stick that flash on top of your camera. I suppose you could rig up a “light tube” around your flash to project a narrow beam when you use that telephoto and regain some of those lost stops. It’s possible to use “commander mode” with your camera internal flash to invoke FP mode, but it gets too complicated. How do I get it? You have to set “Auto FP” mode in your (Nikon) camera. I’m clueless if Canon has it. You need a separate Nikon flash (I use the Nikon SB600, but the 700,800,900 series have it too). When you set a shutter speed faster than your internal flash can handle (like faster than 1/250), the external flash enters the FP mode. If you’re inside, you can just change the shutter speed to the flash sync speed or lower and the flash will automatically exit FP mode and act like a regular flash. Manual mode A related topic is using your camera in ‘manual’ mode with a flash. Guess what? Your flash is still in ‘automatic exposure’ mode, even when your camera is in ‘manual’! Is that great or what? A nice effect to try is to under-expose in manual mode by about 1 ½ stops and let your flash do the rest. The flash will expose your subject correctly (if you’re close enough), but the background will be nicely under-exposed by just the right amount. Indoor shots are somewhat disturbing when the background goes black, and it screams ‘amateur’; use manual mode to get the ambient light levels up, and the flash can correctly light your subject. Nearly every picture is improved when you use fill lighting. Jacking up the ISO isn’t always the best solution to low light, either. #howto