In the previous post we did some testing that indicated that SLR lenses work well on the a7R. In an earlier post, I found some corner casts with the Leica 50mm f/1.4 Summilux ASPH that surprised me. I have not tested that lens for corner smearing; I’m waiting for the diffuser that will let me try out the Adobe Flat Field interleaved workflow. I picked the Leica 90mm f/2 Summicron APO for my next test. If it works out OK, then longer M-mount lenses will too. Exposures were from 1/8000 at f/2 to 1/160 at f/16.
Here’s the scene wide open. Both light falloff towards the periphery and diffuse veiling flare are visible:
f/2.8 removes both to a great extent:
At f/4, the illumination become even, and it stays that way through the rest of the apertures:
For the first series, I focused at f/2 on the trees just over the roof of the house. That part of the image looks like this at f/2 and 1:1:
f/2.8 looks a lot sharper at first glance, but the big difference is the contrast increase due to the reduction in diffuse veiling flare:
f/4 is a little sharper, and f/5.6 is sharper yet:
f/8 is about the same as f/5.6, and it softens up a little at f/11 and a lot at f/16.
The tree at the upper right (it’s the same tree as in the upper right of the wide angle images posted earlier, but from a different perspective) isn’t sharp at the wider f-stops when the camera is focused on the tree over the house, so the next images are all from the series where I focused on the upper right foliage. I think the reason is that the trees are at different distances, although it is possible that there is some field curvature.
f/2 and f/2.8 are about the same sharpness, and they are not bad at all, considering. Here’s the foliage at f/2.
f/4 is crisper:
F/5.6 is a little sharper. f/8 and f/11 are about the same, and the sharpest apertures at this corner. This is f/8:
f/16 is softer, about the same as f/5.6.
So, overall, the best aperture for this lens on the a7R is f/8. The performance is pretty darned good, and there’s no obvious smearing or corner cast to be seen. My guess is that the 135 would also be a good match for the a7R.
The links are to Photoshop files with 12 layers, 6 layers for the center-focused images, and 6 for the upper-right-focused images. The layers are labeled appropriately.