Donald, Rockwell is rarely in doubt, often wrong.

One of the wonderful things about the second generation of Biogons (38/4.5, 45/4.5, 53/4.5, 75/4.5) is that they have rather less than cos(theta)^4 falloff of illumination. And they do have mechanical vignetting. At the edge, illumination falls off precipitously.

Why do I believe this? Because I shoot a 38/4.5 Biogon, ex-AGI f135, on a Century Graphic with a 2x3 back. It covers 84 mm with good illumination and sharpness. Sharpness is maintained to 86 mm, and there the illumination is gone completely. My little camera has nil in the way of movements, but an 84 mm usable circle on 57 x 82 gives useful cropping opportunities. Do the arithmetic.

The 75s cover at least 168 mm. One of my neighbors has a flock of them, also a 45, a coupla 53s, and a small pile of 38s. And the Super Aviogon I mentioned.

John, thanks for the explanation. I fear you've fallen into the "the better is the enemy of the good" trap. But since its your resources and, in the end, your satisfaction, please yourself and be happy.