[Rainer]

[quote name='Plochmann' timestamp='1333691598' post='17341']

I think an f-stop is just an f-stop and sensor sizes are not part of the equation.

[/quote]



You are correct.



A given lens has a certain maximum aperture even when absolutely no sensor or

camera is attached to it.



The maximum aperture as specified on a lens simply describes the ratio between

focal length and diameter of the entrance pupil. With that ... a lens with 17mm focal length

and an an entrance pupil of 18mm has a maximum aperture of f/0.95. Since both,

the focal length as well as the entrance pupil are attributes of the lens (and do

not change with the camera the lens is mounted to), the f/0.95 always applies to such a lens.



Nothing in this definition tells us, that the imagecricle produced by this lens will cover

Mft, crop-1.6 or even FF (135-film). The image-circle produced is another attribute of the

lens, and here, you would find that while it is possible to produce a 17mm f/0.95 for Mft, it

is extremly hard to construct one with an imagecircle covering FF.



Just my thoughts ... Rainer