Effect of aperture and focal ratio on brightness
Hi all,
Considering the move from 12" to 16", and possibly a fast one (f/3.8).
As aperture increases, we collect more light.
As focal ratio decreases (f/8 to f/3.8) exposures can be shorter for the same image brightness.
But is the change uniform for all objects looked at through a telescope? Eg:
- is a star (single point at infinity) brightness increased the same as the image of a distant galaxy?
- is background light pollution brightness increased the same as the brightness of a star (single point at infinity)?
My logic says all are increased equally as the telescope knows no difference between objects, but I have been caught out by this before in discussions on IIS I think? Where people say point sources operate differently to dispersed light sources?
Thanks,
Roger.
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