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Aperture vs F/stop - Newbie Question

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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,


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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.


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