Originally posted by quant2325 Lenses have to be bigger if they are faster since the amount of light that is collected by a particular lens is proportional to the surface area of the aperture.
Uh, huh...actually, it is the diameter of the entrance pupil, but close enough, I fancy. For a 50mm lens, that is only 25mm to make f/2.0. I have a couple of very petite 50mm f/2 FF lenses with a barrel diameter of only about 45mm and an overall length about the same. Both are very well corrected and quite sharp too. That being said, they were made for use of 35mm rangefinder film cameras.
I am not saying that maximum aperture is not a factor. It is, but it is not the entrance pupil size that is driving the increase in size, nor is it those pesky tiny pixels. The huge front elements have more to do with allowing a mirror box that is deeper than the lens focal length and while also providing a decent sized entrance pupil while providing flat field and excellent optical correction.
Steve
(...has a 28/2.5 that is three times the volume of the FA 77/1.8 Limited and which takes a 77mm filter. The FA 77 takes a 49mm filter...go figure...)
Last edited by stevebrot; 09-14-2015 at 08:27 PM.