At 07:15 11.08.01 -0400, Morgan Sparks wrote:
Can someone please explain this?
When doing ordinary photography you will usually encounter objects with a
well defined surface area. That is if you increase focal length your
subject will be rendered larger on film, and the image will then be dimmer.
The solution is to make the lens opening bigger too, to allow for the same
image brightness, and this is where the the f/-number comes in handy.
f/-number is all that matters for extended objects.
Stars on the other hand are not extended objects. In practical terms, now
matter how large a lens you use, the star will still be a point, so a
bigger lens opening will catch more light, thereby imaging fainter stars on
film.
This of course works only if you take care to focus and stop down the lens
enough for the stars to be points and not just blobs.... The 50/1.2 is not
a stellar(!) performer wide open.
Regards,
Thomas Bryhn
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