Question about exposure time.

[thing]

I did 3x4 mins of NGC 891 the other night (first pic) so I thought I would give it an hour tonight, (second pic) 30x2 mins, darks and flats applied. I was a bit disappointed that it didn't come out any better to say it had five times the exposure time of the first. Is it the actual length of the sub that counts for more than the amount of subs?

(click to enlarge)

(click to enlarge)

[Tim]

Hi,

The more subs you take, the smoother the final pic will be. As for detail, thats a bit different. Some darker areas of DSO's will only ever show up with longer exposures, it doesnt seem to matter how many shorter subs you take.

As a general rule with a dslr, expose until the histogram starts about a fifth of the way along from the left side, and dont be afraid to use iso1600 if you can stack up a good number of images. I find that iso800 and 5min subs are about right for imaging at about F6 or so.

Hope that helps a bit. Besides, I would say that the second pic has a lot more contrast and definition?

[steppenwolf]

To my eye, the second image is much better - much smoother and cleaner which is what I would expect with many more subs.

[thing]

Thanks guys. The second shot is smoother I suppose, I just thought there would be a lot more detail on it. Another thread has a similar question and it seems that the consensus is that faint fuzzies need long exposures.