Nikkor 500mm f/5.6 PF with Sigma TC-1401 Teleconverter Review
This is a combination that both Nikon and Sigma tell you not to do. So of course I had to try it out. The reality is that it works pretty well. The official name for this lens is the Nikkor AF-S 500mm f/5.6E PF ED VR.
The Sigma TC-1401 is a 1.4X teleconverter, so you end up with a 700mm f/8 lens. Does this result in some limitations? Of course. Is it still worth it? Of course.
Sigma TC-1401 and Nikkor 500mm PF on Nikon D850
First things first: if your camera doesn’t have f/8 focus points, then don’t use this combination. I use the combo on my Nikon D850 and D500 (for a 1050mm lens). This caution and most other cautions that follow would be the same for the Nikon teleconverter, too.
Before I forget, I need to mention that 3D tracking focus mode doesn’t really work, since it’s pretty much limited to f/5.6 or faster lenses
The Sigma TC-1401 only extends the lens by 20mm, and weighs 1460 grams (6.7 ounces), so you barely notice when it’s attached. Nobody would notice the TC in the shot above if I didn’t point it out.
Focus accuracy isn’t entirely repeatable when using the TC, even in sunlight. Be sure to take a few extra shots of your subject, and you’ll be glad you did.
The camera isn’t aware that there is a teleconverter attached, which means that the EXIF data will still register f/5.6 and 500mm instead of f/8 and 700mm. Also, the camera focus fine-tune data cannot be separately stored for the lens with and without the teleconverter attached. You’ll definitely need to calibrate focus differently when the TC is attached, too.
VR seems to work just fine with this combination; you'll be happiest with "Sport" VR mode for moving subjects.
Please note that you need to attach the TC to the lens before you attach the combination to the camera, or else autofocus won't work.
Focus Speed
I tested focus speed by using 120fps video to observe the focus scale; I set the lens on minimum focus and then focused on infinity in bright light. Minimum focus is 3 meters, or about 10 feet.
I measured 0.400 seconds to focus, which compares to 0.308 seconds when not using the TC. I used my D500 camera, which focuses essentially identically to the D850. I got the time measurement by counting 48 video frames to finish focus, at 0.0083 seconds per frame.
Watching the video of the focus action, I noticed that the lens would over-shoot infinity slightly, back up, and then stop at infinity. This focus-stutter happens much quicker than you can perceive with the naked eye, and can only be observed using high-speed video.
Focus still works in shade, but it’s of course a bit slower and a bit less reliable than bright light.
You’ll be a bit disappointed trying to follow action with this combination in the shade, although it’s not out of the question. The same caution applies to Nikon’s teleconverters, according to what I have read.
Resolution tests
I performed the resolution tests with the lens/teleconverter combination at 20 meters (about 65 feet). Shots look pretty sharp if the resolution stays above about 30 lp/mm. As you’ll see, that’s no problem with this combination, even wide open.
Again, the EXIF data is incorrect for this combination, so the 700mm focal length is reported as 500mm, and shots at f/8 will show up as f/5.6 instead.
I perform resolution tests using “live view” with contrast-detect focus, to eliminate focus calibration from being an issue. I set my camera up to use electronic front-curtain exposure to rid vibrations. I also use a wired remote release. Even contrast-detect focus gives variable results, so I pick my sharpest result (from 10 shots) to report. I always use unsharpened Raw-format shots for testing.
Overall, the following tests show a resolution drop of between 18% to 27%, depending on the aperture (compared to not using a teleconverter). Considering that the focal length is 40% longer, this is much better than merely cropping a 500mm shot.
MTF50 resolution, 700mm f/8
Peak center resolution at f/8 is 42.8 lp/mm, compared to 58.5 without the TC, or a 27% drop.
Peak edge resolution is 44.3 lp/mm.
Peak corner resolution is 36.4 lp/mm.
This is shooting with the aperture wide open (f/5.6 marked, f/8 actual).
MTF Contrast Plot, 700mm f/8
Lateral chromatic aberration, 700mm f/8
MTF50 resolution, 700mm f/11
Peak center resolution at f/11 is 44.4 lp/mm, compared to 54.3 without the TC, or a 18% drop.
Peak edge resolution is 43.7 lp/mm.
Peak corner resolution is 42.8 lp/mm.
This is the best aperture for the combination (1 stop down from maximum).
MTF Contrast Plot, 700mm f/11
MTF50 resolution, 700mm f/16
Peak center resolution at f/16 is 35.1 lp/mm, compared to 47.1 without the TC, or a 25% drop.
Peak edge resolution is 35.4 lp/mm.
Peak corner resolution is 34.0 lp/mm.
MTF Contrast Plot, 700mm f/16
Samples
700mm 1/2000 f/8 ISO 4500. Cloudy conditions. D850
Pixel view
700mm 1/2000 f/8 ISO 7200 Deep shade. D850
700mm 1/2500 f/8 ISO 800 Sunny. D850
Pixel view
700mm 1/3200 f/8 ISO 800
700mm 1/3200 f/8 ISO 800
Conclusion
Honestly, you don’t really even need to stop the lens down for great resolution shots.
Don’t worry about the sharpness loss, but you’ll have to decide if difficulties with autofocus keep you from using this combination. Only using the camera f/8 focus sensors is a bit irritating.
It’s a pain to have to remember changing the focus fine-tune calibration when adding/removing the TC, but such is life. Mirrorless cameras could rid this concern.
Although the focus systems are supposed to have equal capabilities, my D500 seems to work better with this combination than my D850 in low light.
Overall, not bad for a verboten combination.
