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