rscheffler
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rsolti13 wrote:
What is the reasoning behind such a big difference between vignetting with digital M bodies vs film?
rscheffler wrote:
To elaborate on what Kent wrote: while film is 'flat', the emulsion has thickness, is not opaque to light and the silver grains are three dimensional. Strongly non-perpendicular light rays in the peripheral image area penetrate the emulsion at an angle and sill register an exposure on the silver grain within it, though not as strongly as on-axis light rays. If you were to overlay a pixel grid on a piece of film, a peripheral light ray might enter the emulsion in one grid coordinate but ultimately 'register' by striking a silver grain located under a neighboring grid coordinate.
With a digital sensor, the actual light sensitive parts of each pixel are typically fairly deep within a pixel well. Strongly non-perpendicular light at the image periphery may not make it directly down to the pixel and instead hits the pixel walls and perhaps is scattered from there down to the light sensitive area. Here micro lenses at the top of the wells help to redirect the light down, but apparently are not 100% effective, which is also dependent on optimal micro lens shape to redirect light to the pixels.
Think of it this way, light from the far edge of the wide open exit pupil travels at a 'steeper' angle to reach a pixel at the opposite edge/corner of the sensor array. Meanwhile light from the near side of the exit pupil travels more directly/perpendicular to the same side of the exit pupil, but this won't offset the effect because pixels in the center of the array more or less see all of the light from the exit pupil.
As the lens is stopped down, light from the exit pupil is seen more consistently from all pixel coordinates across the sensor. The light is seen more from the optical center, whereas when the lens is at a wider aperture, a greater portion of the light travels through portions of the exit pupil that are masked by the pixel walls.
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rsolti13 wrote:
Thanks Ron, so you pretty much answered my question above...should be no discernable difference between monochrom vs color digital camera
That is my layman's understanding of the phenomena. It's possible that sensor toppings can also have some effect, such as removal of the CFA for the Monochrom model. But I can't recall seeing side by side comparisons of vignetting characteristics made on the same color and monochrome versions of past M cameras, so can't say whether this has been the case. Perhaps this is an opportunity for someone with both the M11 and Monochrom to do a quick comparison? 
I'd be surprised if it isn't very similar.
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