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.
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.
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.
I couldn’t see any changes to lens distortion when using the teleconverter, either.
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
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.
You won’t notice any sharpness loss. 98mm f/4.0
Closest focus, 280mm f/4.0 It’s the bee’s knees
It doesn’t mess up those out-of-focus backgrounds.