Lens Sharpness, Contrast and Color Rendition
Similar to AF performance, lens sharpness, contrast and color rendition will depend on the lens the TC-20E III is coupled with. Fast prime lenses generally yield the best performance, but still require stopping down in order to get optimal results. No matter what lens you use the TC-20E III with, image quality will be degraded in all cases to a certain extent, even with top-of-the-line lenses like Nikon 200mm f/2G and Nikon 300mm f/2.8G. Sharpness improves dramatically as you stop down on the aforementioned lenses, but still does not reach the same level of sharpness you would get without a teleconverter, which is expected. Colors and contrast are OK at maximum aperture and also improve when stopped down. I personally would not use apertures faster than f/8.0 (except on Nikon 200mm f/2G, which is very sharp at f/5.6) when using the Nikon TC-20E III if you want to get the best results.
Sharpness Test – Nikon 70-200mm f/2.8G VR II with TC-20E III Center @ 400mm
A couple of notes and observations before moving on to sharpness tests. I found the TC-20E III to work very well with the Nikon 70-200mm f/2.8G VR II for stationary and slow subjects. For fast-action photography (birds in flight, running wildlife), the autofocus on the 70-200mm was the bottleneck – I did not get many sharp images due to focus errors. The experience I had with the TC-20E III on 70-200mm VR II was very similar to the TC-17E II on 70-200mm both in terms of sharpness and AF accuracy, although the TC-17E II produced slightly better results with fast-moving subjects. Unfortunately, the previous generation Nikon 70-200mm f/2.8G VR does not pair well with the TC-20E III or the older TC-20E II (in my opinion, the older TC-20E II is basically unusable with any lens as there is too much image degradation and loss of contrast). So if you own the older 70-200mm f/2.8G VR and want to try the TC-20E III, you will most likely be disappointed. It almost feels like Nikon “tuned” the 70-200mm for the TC-20E III before they released it. Overall, I am very pleased with how the TC-20E III performed with the Nikon 70-200mm f/2.8G VR II.
I only tested the Nikon 70-200mm @ 200mm (400mm effective) for two reasons: the lens is incredibly sharp at all focal lengths and those who will be using the 70-200mm with a 2x TC will be using it at the longest focal length to get the maximum reach. Wide open at f/5.6, the Nikon 70-200mm f/2.8G VR II shows pretty good sharpness. Stopping down the lens to f/8 improves the situation significantly, as can be seen below:
As you can see, stopping down to f/11 does not improve sharpness and anything smaller than that shows the negative effects of diffraction.
Sharpness Test – Nikon 70-200mm f/2.8G VR II with TC-20E III Corner @ 400mm
The first image is darker due to visible vignetting at the largest aperture. If I brighten up the image a little, there is no difference between the two images. This means that stopping down the lens does not result in improved sharpness in the corners. Let’s see if the situation improves at f/11 or f/16:
I cannot see any improvements at smaller apertures at all.
Nikon 70-200mm f/2.8G VR II + TC20E III vs Nikon 200-400mm f/4G VR
Obviously, the Nikon 200-400mm is much sharper wide open without a teleconverter. Once you use the TC-20E III with the 200-400mm, the performance goes down the drain, as can be seen in other tests of this review. Here is a more meaningful comparison with the 70-200mm at f/8:
As you can see, the TC-20E III yields surprisingly good results with the 70-200mm at f/8, which is pretty close to the 200-400mm at f/4 (without a TC) in sharpness. Obviously, there is a loss of two full stops of light and larger depth of field, but still pretty impressive.
Sharpness Test – Nikon 300mm f/2.8G VR II with TC-20E III Center Frame
The Nikon TC-20E III was specifically designed to pair well with lenses like Nikon 300mm f/2.8G. I had a very pleasant experience with the TC-20E III both in terms of sharpness and AF speed on the 300mm f/2.8G VR II. I was able to photograph birds in flight with this combo and images were sharp enough wide open and very sharp at f/8. If you have an older version of the 300mm f/2.8 lens, you can safely assume that the TC-20E III will give you similar results. As I have already noted in my Nikon 300mm f/2.8G VR II Review, I would rather use the Nikon 300mm f/2.8 with the TC-20E III than the Nikon 200-400mm f/4 with the TC-17E II or the TC-14E II.
Stopping down the lens to f/11 does nothing and at f/16 diffraction kicks in and makes the image look a little softer:
If you want the best results, I recommend keeping your aperture at f/8. Larger apertures between f/5.6 and f/8 can also yield fairly good sharpness in the center. Let’s take a look at the corners now.
Sharpness Test – Nikon 300mm f/2.8G VR II with TC-20E III Corner Frame
Sharpness Test – Nikon 300mm f/4 AF-S with TC-20E III Center Frame
I love my Nikon 300mm f/4 AF-S, because it is a very sharp and lightweight lens that I take with me when I do not feel like taking the big bazookas with me. While it pairs very well with the Nikon TC-14E II, I find it to be unreliable with any other teleconverter. I have tried the TC-20E II with the 300mm f/4 AF-S in the past and found it to be completely unacceptable, so I decided to try it again with the new TC-20E III. The Nikon TC-20E III slows down the Nikon 300mm f/4 AF-S to f/8. As expected, the small maximum aperture of the lens caused the AF system to be completely unreliable and often inoperable – the lens would hunt in almost all cases. I quickly gave up using the TC-20E III. Let’s see how sharp the optics of the Nikon 300mm f/4 AF-S are with the TC-20E III if you were to manually focus:
The wide open performance of the 300mm f/4 AF-S @ f/8 is slightly worse than when stopped down to f/11.
Stopping down the lens further to f/16 does not improve the sharpness.
Nikon 300mm f/4 AF-S + TC-20E III vs Nikon 300mm f/2.8G VR II + TC-20E III
As you can see, the Nikon 300mm f/2.8G VR II + TC-20E III is much sharper at f/8 when compared against the Nikon 300mm f/4 AF-S + TC-20E III. If you compare both lenses wide open (at f/5.6 and f/8.0), then they look very similar as seen below (Left: Nikon 300mm f/4 @ f/8, Right: Nikon 300mm f/2.8G @ f/5.6):
I am not going to provide test results from the Nikon 300mm f/4 AF-S in the corners, because it performs very similarly to the Nikon 300mm f/2.8G.
Sharpness Test – Nikon 200-400mm f/4G VR with TC-20E III Center Frame
I had a negative experience with the TC-20E III mounted on the Nikon 200-400mm – not only did autofocus not work, but I could not get good sharpness out of this lens, period. Without a teleconverter or with the Nikon TC-14E II, the 200-400mm is extremely sharp from center to corner across the zoom range. But it just does not play well with the Nikon TC-17E II, Nikon TC-20E II and the new Nikon TC-20E III. Take a look at the performance of the lens at 600mm:
As you can see, the wide open performance at f/8 is weak and stopping down the lens to f/11 does nothing to improve the sharpness – the same goes for f/16:
The corner performance is very similar to center performance.
Nikon 200-400mm f/4G VR + TC-20E III vs Nikon 300mm f/2.8G VR II + TC-20E III
Again, the Nikon 300mm f/2.8G is much sharper and the two would be comparable wide open.
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