DSLR widefield sub length

[jambouk]

When imaging widefield with just a DSLR on an equatorial mount (say at 35mm focal length) is there still a drive to get the longest possible subs (avoiding excessive sky glow of course and tracking deficiencies), to maximise the signal to noise ratio? Or, for whatever reason, is it less important?

I was asked, and I wasn't sure of the answer other than just assuming the same principles apply whether using a scope targetted on a small galaxy or a wide angled lens looking at the milky way.

Interesting to hear what others think.

James

[Alien 13]

Good question I know with my kit very wide angle is limited by sky brightness so the max exposure time can be quite short maybe 30 sec to 2 mins, the other issue is sky gradients which may produce some strange effects with very long exposures.

Alan

[Scooot]

From what I've read,with widefield and just a dslr, the lens you're using takes on more importance but essentially other aspects are the same. This is a good read.

http://www.randombio.com/astrophotography-without-a-telescope.html

[ericxbenedetti]

I go for low ISO and longest exposure to generate a histogram where the curve is about 1/3 from the left when I'm using my skytracker. This way colors are natural and highlights are not overblown. You never want to go over ISO 1600 anyways with modern dslr cameras because they are ISOless above that point, meaning it's all post sensor digital gain which does nothing to help signal to noise. As long as your tracking you should expose the length of time necessary to generate a proper curve. That will depend on the amount of light pollution in your area.

I can't ever get more than 2 minute subs with my 24mm f1.4 lens unless I'm in very dark skies. Keep in mind you want a lens that has a decent focal length (I'd say 24 to 35mm) and can go really wide open, like f1.8 or more open. These lenses are far more light sensitive and you'll capture a ton more stars compared to an ultra wide angle f2.8 that are so common.