Quote:
Originally Posted by Slawomir
I thought this only applies to stars, not extended objects, for which the faster the f-ratio the stronger the signal regardless of aperture given the same arcseconds per pixel and same RN and same QE and... 
I believe the main advantage of a larger aperture when doing pretty DSO pictures is smaller spot size. |
Photons are photons...they’re all the same to the pixels (ignoring their QE curve which is just their response to different wavelengths). An example of another extended object, which is easy to test, is the Moon...which is noticeably brighter in a larger scope.
Signal only gets stronger with fast f-ratio because the light cone gradient is steeper which results in more photons being focused in the same area of sensor.
All things considered, a larger scope is always going to collect more photons than a smaller one.