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Telephoto Test: The Canon 300 f/2.8 IS II

The Canon 300mm f/2.8 IS II is a really sharp telephoto lens that is still small enough to work with easily in the lab. We shot all 3 cameras through the same copy of the lens. Mirror lock up, 10 second timer, focus bracketing, and all the routine techniques used in all our other Imatest articles were used. The table below shows the resolution differences between the original 5D Mk III and the two newer cameras when shot through the same copy of the lens.

Resolution increased about 30% when moving from the 5D III to the 5DS in the center and for the average of the entire surface of the lens, which was about what we had expected. Resolution in the absolute corners increased about 20%. This isn't shocking since we would expect the corners of the image to be more limited by the lens (although I had hoped such an excellent telephoto lens might do a bit better).

I was a bit surprised at the difference between the 5DS and the 5DS R in this test. The 5DS R version provided about a 10% increase in resolution over the 5DS.

 Standard Range Test: The Zeiss 85mm f/1.4 Otus

We were wanting to make this test about the cameras more than the lenses so we chose one of the sharpest standard range lenses we could think of, the Zeiss 85mm f/1.4 Otus. We repeated the test the same way, shooting at f/2.8 again.

With the Zeiss 85mm Otus things are just a bit different. The improvement between the 5D III and the 5DS is about 20% in the center, slightly less off-axis. The 5DS R version adds about 5% more resolution compared to the 5DS. I was a bit surprised at the result and repeated it several times to confirm the numbers and it was so. The reason I was surprised is the Otus is the highest resolving lens, and my first thought was it therefore would benefit the most from the higher resolution cameras.

Wide-Angle Test: The Zeiss 21mm f/2.8

For this test we moved back to our largest printed paper resolution chart and are shooting even then at a fairly close distance (about 9 feet). The Zeiss 21mm f/2.8, old as the design is, is still on of the sharpest wide-angle lenses in the edges and corners.

Again, we see the resolution is greatly improved, with the 5DS MTF50 numbers about 30% higher than the 5D Mk III, even in the corners. Throughout most of the image, the 5DS R MTF50 numbers are about 10% higher than the 5DS. However, in the absolute corners there is only a small difference between the 5DS and 5DS R cameras. From other things we know about this lens, I would assume this is because the corner resolution with this lens is limited by astigmatism.

I want to clarify this just a bit because depending upon how a tester is presenting data, you may see them present this corner data differently. Imatest doesn't measure astigmatism exactly, but does measure slanted lines that are nearly vertical and nearly horizontal. When I present corner data I average 8 numbers: the horizontal and vertical reading in each corner. Someone else may present only the best corner number, or the median corner number, or just vertical or horizontal numbers. This might have a corner number better or worse than what we are presenting.

The Not So Great Lens Test: Canon 50mm f/1.4

I wanted to add this to make a point. I'm beginning to read people discussing "50-megapixel capable lenses" and I'm afraid it creates some confusion. It's true, these high-resolution sensors are going to magnify the difference between lenses. But that doesn't mean they don't benefit every lens. With this in mind I went and found a battered old copy of the Canon 50mm f/1.4 lens. This is a decent, although few would claim fabulous, lens. This particular copy was also very slightly decentered. It wasn't even the best of the 50mm f/1.4. I test all three cameras with this lens just like I did the others (except this test was done at f/1.4 -- I want the lens to be just as weak as it could be).

Even with a weak copy of an average lens, there's no question the high resolution sensors improve the resolution, at least in the center. The improvement isn't as great as it is with the excellent lenses we tested above. The 5DS had about 20% better resolution in the center and as an average compared to the 5D III. Corner resolution, though, changed very little. The difference between the 5DS and 5DS R was also negligible with this lens. But there's no question even a weak lens shows significantly improved resolution on the new cameras.