Schneider 90/4.5 Apo-Componon HM on GFX 50R

The Schneider 90/4.5 Apo-Componon HM is an enlarging lens that I happen to have lying around from my film days. I remembered it as a great enlarging lens. I wondered how it would perform in a completely different role: as a camera lens. This is asking the lens to perform well outside of its comfort zone. It was designed for reproduction ratios on the order of 8:1, which would be a really tight portrait with the GFX 50R. I’m tested it at a much greater distance, about 12 meters. I also tested it wide open. The full opening was designed to be used for focusing.

First, you might ask how I got the lens mounted to the camera. Here’s how:

The “lens adapter” is a Cambo Actus.

Here’s my test scene:

And here’s a look at the target, with the lens wide open.

In the center:

And in the corner.

You can’t judge light falloff from those because I goofed and used automatic exposure.

Test protocol:

• 12 meters target distance
• ISO 100
• f/4.5
• Subject in the center and the upper right corner.
• Manual focusing.
• Six shots at each setting, focusing anew for each shot, picking the best using the Imatest sharpness ranking utility. This method calibrates out focus curvature.
• Developed in Lightroom
• Sharpening set to zero.
• White balance set to gray background on Siemens Star target
• Adobe Color Profile
• Minor exposure adjustments, with same adjustment applied to all images from both lenses, so corner darkening is unaffected.
• Chromatic aberration correction turned off.
• Everything else at default settings

MTF testing using the slanted edge follows.

In the center:

That is quite sharp. Lots of aliasing, thanks to the small pixel apertures on the GFX 50x cameras.

In the corner:

That is still quite sharp. I was hoping for a bit better performance, since the lens was made to cover a 6×6 negative.

Here are the MTF calculations at various angles using the star part of the target:

Same data in a spider plot:

And, finally, a Shannon information capacity plot. I’m still trying to figure out how to use these:

This is good performance, but with respect to the corners, my socks are firmly in place. I’ll try stopping it down a bit.