Aperture vs F/stop - Newbie Question

[Leedsgreen]

Dear All,

At the moment I'm having a go a imagine DSOs using a LX modified webcam and my 400mm SW Equinox 66 refractor (66mm aperture, f/6). My question is, is it the f/stop alone that determines how much light a scope can 'pull in' or the aperture as well?

What I mean is, will a 120mm f/6 scope will require less exposure time than a 66mm f/6 scope (to achieve the same image)? My sense is that the bigger aperture will have a big effect?

Thanks for any help,

Nick

[roundycat]

For extended objects exposure depth is mainly determined by the f ratio. The bigger the aperture the better will be the angular resolution, all other things (such as the sky condition) being equal.

Dennis

[Leedsgreen]

Hi Dennis,

Thanks for your reply, much appreciated. (I actually re-posted this question in the 'help' section and have received further useful replies there).

Nick

[ollypenrice]

Yes, this comes up a lot. A slow scope is, on non point sources, a slow scope, however big it is. And vice versa, a small fast scope is still fast. If you want to get DSOs to show on a webcam you want all the speed you can get plus a short FL so things will fit on your small chip.

Olly

[Leedsgreen]

Magic, thanks Olly.

Nick