You know what else you couldn't fit in your front pocket? Your M3 with any other normal Leica lens that doesn't collapse. Try doing that trick with a 50 'cron which would be a much realistic comparison.
Originally Posted by okto
The only real difference in size is the prism and that's a given seeing that its an SLR. As someone who owns both an F3 and an M4 and used them together countless times I'm simply stating F3 size is a non-issue and on the smaller end of the scale.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.