> Does the f-stop change when a medium format lense is placed on a
small
> format camera?
>
> If so, would the f-stop be bigger or smaller?
The focal length of a 100 mm f8 lens is 100 mm f8
This sounds like the sort of question that should only be asked by
stupid people. "Should" is the operative word. Simple answer: the
focal length and aperture of a lens are properties of the lens alone.
So why are stupid questions so common? So called "information"
from camera mags does not help.
Myths:
1) A smaller film format (APS, CCD) increases the (effective) focal
length of a lens
2) A 2x converter doubles the (effective) focal length of a lens
3) An image stabiliser reduces the (effective) aperture.
4) Adding extension tubes reduces the (effective) aperture.
The word "effective" is crucial in all of the above but often gets
skipped - it sounds like a throwaway line. Trouble is it is not self
explanatory. It is up to the user to define "effective" according to
circumstances.
For the film format (1) it is just a way of saying "if you crop an
image the small bit in the middle fills more of the frame" [you
should have used a longer lens and kept quality]
For extension tubes (4) it just says that at macro scales (high
magnification) you need to account for the inevitably reduced image
illumination.
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