I've never really stopped to think too much about how telescopes work and how the combination of focal length and aperture work together to produce images of a certain brightness and field of view, so now that I am thinking about these things, I find I have questions.
Stan Moore has an interesting article on the
F-ratio Myth basically saying that varying the F-ratio does nothing for exposure time, only varying the aperture makes a difference.
On the face of it, this makes sense... focal length controls FOV, aperture controls the amount of light. Bigger aperture means a bigger light bucket and thus more light.
But why does a bigger aperture mean more light from the same source? Shouldn't it mean more light, but from different sources? Take a point light source, it doesn't seem like it should matter whether you have a 80mm aperture or a 500mm, it's a point source, so it seems like you should either get it or not.
Does it work differently for point light sources and diffuse light sources?