Nikon TC-17E II Lab Test
I recently picked up a used Nikon AF-S Teleconverter (TC) TC-17E II and put it through some controlled lab tests. A more comprehensive "field" test will follow, but I'm increasingly more interested in testing certain things in the "lab". In particular with this teleconverter, I wanted to test whether I get an increase in image quality over the 1.4 teleconverter.
Notably, the Nikon 1.7x teleconverter, released in 2004, gives you a 70% increase in focal length, but at the cost of 1.5 stops of light. This is in contrast to the 1.4x teleconverter which gives you a 40% increase in focal length at "just" a stop of light. The 1.4x TC is one of my favorite pieces of kit when paired with my 500mm and 300mm f/4 lenses (making them 700mm and 420mm f/5.6 lenses). I'm very happy with 700mm on my crop body, but you can never have enough focal length, and I thought the 1.7x TC would be a great compromise between the 1.4x TC and the 2.0x TC. Notably, the bare lens is an f/4 lens, while with the 1.7x TC it is an f/6.7 lens.
For this test, I used the Nikon 500mm f/4E lens. This is a spectacular lens that is amazingly sharp, a dream to use, and takes the 1.4x TC very well. There is very little loss of quality with the 1.4x, so much so that I honestly can't notice a difference when examining files at 100% (i.e. a pixel from the original capture is now a pixel on your screen).
Using a $10 note from NZ, I photographed the high contrast target using a tripod mounted 500mm f/4 +/- TC on my D500. Each pair was auto focus fine tuned -- with the bare 500mm and 500mm + 1.4x TC resulting +0 adjustment, and the 500mm + 1.7x TC resulting in a +2 adjustment. Below you can see a slight crop (not 100%!) of the image with each pair, showing the magnification of each TC. Each image was taken at 1/250, wide open, at ISO 500, 1,000, and 1,600 respectively.
However, looking at 100% is where the real test begins. As mentioned, the bare lens and lens + 1.4x TC are very sharp, and I don't think I need to show 100% crops to prove that. However, I have more questions and doubts about the 1.7x TC, even when paired with a high quality lens.
For this test, I took a series of 10 images from each combo listed above and visually picked the sharpest image. I cropped each image to contain the same tight face crop, and then upsized the 500mm f/4 image and the 500mm + 1.4x TC image to contain the same number of pixels as the 500mm + 1.7x TC 100% crop. From here, we can visually compare each sample, as shown below. Click the image to see at full size (2,000 pixels wide).
Clearly, the image taken with the 1.7x TC and the upsized 1.4x TC beats the bare 500mm f/4 image upsized. This is no surprise as upsizing a file 70% is too much to ask for any lens.
However, things get tricky when comparing the upsized 1.4x TC image against the 1.7x TC image. I can say when examining closely on my computer that the 1.7x image *IS* a bit better! Lines are just ever so slightly sharper with a touch more "edge". However, it is *only* just a bit better. And you lose 0.5 stops of light compared to the 1.4x TC, and autofocus speed does decrease (however, field tests will determine how much this matters).
So whats the verdict? Well, the ultimate test is how this TC fairs for "in the field" bird and wildlife images. At the end of the day I don't photograph dollar bills, so if I can get a benefit from the TC (e.g. larger subject to AF on, etc) then that could be a benefit. However, if I don't get much more image quality than the 1.4x TC AND I lose a 1/2 stop of light (as things appear here), that starts to hurt, and I can put that money into something else for my photography (e.g. memory cards, cold weather gear, etc). Field test will provide the ultimate verdict, but I'm glad to get the insight from a controlled, purely image quality based test, and perhaps this post will help others decide for themselves.
As always, feel free to follow me on social media (links above), or comment with questions / comments.