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like i said, i know how it works in telescopes... say a refractor where a aperture of 80mm has better light grabbing ability than a 60mm. but the aperture of a camera lens is controlled at the back of the lens (and yes still controls the light handling), but how about the front of said lens?
is a 300mm f4 lens set at f4 going to capture as much light as a 300mm f2.8 set at f4? if so then whats all that extra glass at the front doing exactly? they take different filter sizes because the front of the f2.8 is soooooooooooooo much bigger.
my head is going to explode i think.
taken the above 2 300mm lenses as an example, we know the aperture which we control and which controls the light is at the back of the lens right? why not then make the f2.8 the same physical size as the f4?
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