A fellow photographer recently asked me how much image degradation one would see with each Nikon teleconverter. As a nature photographer, I have been wondering myself about this for a while, but never had a chance to actually quantify what the image degradation figures would look like when using the TC-14E II, TC-17E II and the TC-20E III with Nikon lenses. I have been relying on field use and my vision so far and here is what I have thought about each teleconverter.
The Nikon TC-14E II is excellent. I have not seen it degrade image quality on any Nikon lenses to the level where I could see an obvious loss of contrast or sharpness. I have used it with the 105mm VR, 70-200mm f/2.8G VR (the old one, as well as VR II), 300mm f/4 and pretty much on every expensive super-telephoto lens. I take it with me everywhere and mine stays pretty much glued to my favorite Nikon 300mm f/4 AF-S the majority of the time – that’s what I use primarily for birding. When shooting with my Nikon 200-400mm, I don’t hesitate to use the TC-14E II, because it does a very good job sharpness and contrast-wise and AF stays accurate and fast. It is obviously the smallest and the lightest of the three.
The Nikon TC-17E II is a mixed bag. It works with many Nikon lenses, but it slows down AF and impacts AF accuracy. Not as good of a TC to be used with slower f/4 lenses, which includes the 300mm f/4, 200-400mm f/4 and 500mm f/4 lenses. I tried to use it with my 300mm f/4 and it makes the lens hunt a lot, especially in anything but good light environments. The same thing with the Nikon 200-400mm f/4, even with the latest camera bodies like Nikon D4. Because of this, I rarely use mine. On fast f/2-2.8 lenses, however, it does pretty well. It works great on the Nikon 70-200mm f/2.8G VR II and it does not disappoint with the 200mm f/2, 300mm f/2.8 and 400mm f/2.8 lenses.
The Nikon TC-20E III is much better than its predecessor (which was very disappointing with many lenses). I was pretty shocked to see it perform very well with the 70-200mm f/2.8G VR II (stop down to f/8 for best results), because the 2x TC was always known to be bad with zoom lenses. It works like a champ with the 300mm f/2.8 and 400mm f/2.8 lenses. On slower f/4 lenses, however, it is still pretty disappointing. It is unusable on the Nikon 300mm f/4 and 200-400mm f/4 lenses and while it will work with the 500mm f/4 and 600mm f/4 lenses, you will have to stop down to f/11 to get anything reasonably good and you will need to use one of the latest Nikon DSLRs like D4 that can handle f/8 lenses. Not a great setup for fast action, but could work for large animals from a very long distance.
Today, I decided to quantify the loss of sharpness using Imatest. Armed with a brand new Nikon 70-200mm f/2.8G VR II and all three TCs, I set on the quest to measure sharpness without a TC first and then with all three TCs separately at the focal lengths of 70mm, 100mm (1.4x), 120mm (1.7x) and 140mm (2.0x). Here are the results that I got:
For most people, these numbers don’t mean anything. I did the math to figure out the percentages and once I compiled the mean data, here is what I came up with:
- Nikon TC-14E II – 5% Sharpness Loss
- Nikon TC-17E II – 17% Sharpness Loss
- Nikon TC-20E III – 26% Sharpness Loss
Now keep in mind that this is the best-case scenario, when everything is stopped down. All four were shot at f/8, ISO 100 on the Nikon D800E. So it is stopping down a lot for the lens alone, by two stops for the TC-14E II (from f/4 to f/8), by a stop and a half for the TC-17E II (from f/4.8 to f/8) and by one-stop for the TC-20E III (from f/5.6 to f/8). I figured f/8 would be a sweet spot for all three TCs. The TC-20E III is slightly better at f/11, but by very little. Beyond f/11 diffraction kicks in and you start seeing image degradation instead of improvement.
As you may already know, maximum aperture changes when using teleconverters. If I shot these wide open, the numbers would be totally different. All teleconverters behave differently at maximum aperture, with the TC-14E II having the least impact on sharpness and both TC-17E II and TC-20E III having the most (I would say both are fairly soft wide open, depending on what lens you mount them on). Also keep in mind that this test only shows performance on one lens – TCs vary in performance on different lenses. You can expect both the TC-17E II and the TC-20E III to behave differently (better) on fast prime lenses like 200mm f/2, 300mm f/2.8, etc.
In summary, when using teleconverters in the field, you could expect the 1.4x teleconverter to lose about 5% sharpness, 1.7x to lose 17% and 2.0x to lose 26%. The TC-14E II is a no brainer here – with only 5% sharpness loss, you won’t see any difference between the original and with the TC attached. All three will look great if you are down-sampling, but differences will be visible when doing 100% crops. For birders, this means that you might not see that same level of detail on feathers and hair that you would see when using the lens without any TCs, or with the TC-14E II attached.