I have a decent set of regular EF-S lenses to use on my NEX MILC, but I want to play around with some toy lenses. I'm particularly interested in C-mounts, because of the size and portability. Most of the 35mm c-mounts seem to produce soft vignetting/distortion, but nothing terrible. Anything else, however, is a toss-up. I've seen uncropped images of 50mm c-mounts on an APS-C sensor without significant vignetting--but I've seen just as many where the lens itself obscures most of the image (like the below image). Is there anything I can look for that would predict whether or not a lens would produce that sort of intense vignetting/obscuring? specifically, would a lens with a throat size of ~42mm automatically produce intense vignetting on a NEX?