Why are there different objective lens sizes? 52 vs 72 etc.

TedG954

Senior Member
Why are some lenses larger, or smaller, on the objective end? Obviously, they all have to be the same size on the connecting end, but does a larger objective allow more light? Yet, a 52mm and a 72mm can share the same 3.5 or 2.8.

My 18-55 is 52mm; my 55-200 is 52mm; my 35mm prime is 52mm; my 24-120mm is 72mm...... my research has found no really definative answers? If 52mm is "best", why aren't all 52mm? If 72mm is best, why not all 72mm?

Why aren't all lenses the same size? :confused:
 
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Mike150

Senior Member
Hey Ted,
Don't know a good "expert" type answer for you (I'm not that smart). What I do know is that the overall diameter of the lens is related to a combination of the max Aperture (lowest number) and the focal length of the lens. I believe the actual formula is Focal Length / F-Number. Actually I'm hoping this will buy a little time until one of the really smart members can give you a real answer.
 
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