Quote Originally Posted by SoulSurround View Post
By the way, is it likely for one distagon to vignet more than another... in other words: can there be significant vignetting differences between lenses in the same series?
Unlikely. This phenomenon follows the fundamental principles of geometric optics - the reduction in relative illuminance closely approximates the fourth power of the cosine of the angle by which the object point is off the camera axis (measured in "object space" at the center of the entrance pupil of the lens).

My 50mm Zeiss Distagon images show cosine 4th illumination falloff and so do images made with my 50mm MC Zeiss Flektagon, plus my 65mm and 45mm Schneider Super Angulons, my 55mm Apo Grandagon and my 110mm Schneider Super Symmar XL (it gives especially obvious illuminance falloff towards the edges of an 8x10 negative). If you don't like the effect, you can use one of the special compensating Schneider or Zeiss filters.