Schneider 90/4.5 Apo-Componon HM on GFX 50R, f/5.6, f/8

Yesterday  I reported on the performance of this Schneider enlarging lens on a Cambo Actus-attached GFX 50R wide open. In the corners, the results were good but not great, so I repeated the test with the lens stopped down to f/5.6.

Test protocol:

• Manual exposure, the same for all images
• 12 meters target distance
• ISO 100
• f/5.6
• Subject in the center, the upper right corner, and the upper right corner with a 5 mm fall.
• 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.

Although the back standard of the Actus is the one you use for rises and falls, the markings on the camera are as if you were moving the front standard. Rise means the back standard drops. Fall means it rises. Ignore the diffraction limited line. Imatest thinks this is a f/1 lens. Now we’re seeing performance that doesn’t fall off much even when we demand a 60 mm image circle which were doing in the bottom chart above.

Stopping down to f/8:

Looks like f/8 is the sweet aperture for this lens. It also looks like there’s some room for movements.

I couldn’t get the Siemens star target to work right in the corners on this test. Sorry.