Originally posted by wombat2go I read that in early days, apertures were placed in front of lenses. They do not vignette, they act to stop down.
As well as acting as a (probably more efficient) hood, for a 50 mm lens with a 28 mm hole in the adaptor ring, the lens has a new f/ number of 50/28 = f/1.8
I will try this on a f/2 50 mm
I've thought about that too, but I always get confused. Is the max aperture related to the smallest element or the smallest point the light passes through? Because surely the big 300/2.8 lenses (nevermind Sigma's monster) and even Pentax's 560/5.6 would need a lens mount 10 cm wide for it to be related to the thinnest point the light passes through.
Perhaps it's related to the largest refraction that can take place from the optical axis? Anyone know more?
And for the record I can't see any difference in the photos posted, though it is only half a stop...