[Atmos (Colin)]

Originally Posted by SimmoW

Oh dear Colin, we shouldn't go down that path! Let's save time and link to other discussions! https://stargazerslounge.com/topic/2...ging-worth-it/

Skimmed over the thread, I do agree with the F/Ratio myth to some extent. Take Ray's SW 10" F/4 with ASI1600. It will work exactly the same as a 10" F/8 as long as the camera has 7.6 micron pixels (given the same QE and read noise). Aperture remains the same as does the pixel scale (~0.78"/pixel).

If aperture alone determined exposure length then a 14mm lens would take hours to get above read noise. It is all about image scale against aperture. Sub exposure time is determined by image scale and sky brightness.

A 50mm lens at F/5 and a DSLR will have the same exposure time as it used on a F/5 10" newt if used at the same location and sky brightness) The difference between the two will be resolution and contrast.