This is a continuation of a test of the following lenses on the Sony a7RII:
- Zeiss 85mm f/1.8 Batis.
- Zeiss 85mm f/1.4 Otus.
- Leica 90mm f/2 Apo Summicron-M ASPH.
- AF-S Nikkor 85mm f/1.4 G.
- Sony 90mm f/2.8 FE Macro.
The test starts here.
Horshack, a poster on DPR whose opinions and methods I respect, said that he had achieved more repeatable autofocus results with a target that he had devised rather than using a Siemens star as I did in the previous tests. Leaving no stone unturned in my efforts to track down the a7RII/Batis 85 misfocusing issue, I ran a test with his target.
Here’s the Horshack target:
I lit a slanted-edge target with two Westcott LED panels, and set the color temperature to 5000K. This is the target, with the Horshack grid in the center.
I mounted a Sony a7RII with the Batis 85/1.8 attached to the Cognisys computer-driven focusing rail. I set the controller up to use 192mm of travel and make 49 exposures 4mm apart. I set the assembly 8 feet from the on-axis target, mounted the lens, focused a little short of mid-rail using manual focusing, and focused on the grid using AF-S with flexible spot, AF priority, small spot size. I exposed 49-shot series with the lens wide open. I used Jack Hogan’s Matlab program, MTF Mapper, and DCRAW to pick the horizontal edges and calculate the MTF50s for the raw color planes, imported the data into Excel, and plotted the results in cycles per picture height vs subject distance change.
The manual focused results for a horizontal edge:
Because I noticed a little anisotropic behavior, here are the curves for a vertical edge:
Not much difference, but a little.
The AF results for the horizontal edge:
About what we saw before. Notice there’s one point early in the series where the camera came closer to getting the focus right.
And for the vertical edge:
Not quite so bad. In fact, the point that the camera got close on the horizontal edge is where it looks like it pretty much nailed the vertical edge. The anisotropy appears to be in the focusing system rather than the lens.
Whatever small differences there are, it doesn’t look like the Siemens star focusing target was the source of the problem.
Jack Hogan says
Interesting. Looks like results are getting more and more consistent. How steady does the Cognisys rail feel from one end to the other of its range?
I tested it a while back for something else, and, with EFCS on, it’s solid.