What length of subs to take?

[alcol620]

Hi folks

Grateful for any views on the following.

For images such as those with lots of nebulosity and detail that needs to be captured, is it better to take a smaller number of longer subs or a greater number of shorter subs.

For example, take 50 X 300s subs or 25 X 600s subs or say 12 X 1200s subs. What is the best way to go about it and why? I realise that the more subs the better for any exposure length.

Look forward to feedback

Thanks

Alec

[StuartJPP]

Hmmmm...been only a couple of weeks since this came up...I await the arguments to follow...

Personally I'd go for as long individual subs as you can without star trailing and not burning out the cores/stars.

Of the above I'd probably do the 2nd with my kit because it will be easier to achieve under UK weather than the 1200s one.

[alcol620]

forgot to mention. Subs taken with a moded DSLR camera

[ollypenrice]

Because the DSLR isn't cooled it risks a big build up of thermal noise. I don't use DSLRs but the folks I know who do use them tend to stick at about 8 minutes. If you have skyglow problems before that point then they'll need to be shorter.

DSLRs tend to give colour mottling in the background, too, so a dither of about 12 pixels and a lot of subs is what Tony Hallas recommends. This will help you get a decent colour in your background sky.

DSLRs have shallower well depth than CCD, too, so saturate more easily in long subs.

Olly

[alcol620]

Thanks for inputs, I will take account of these when next imaging takes place. I have been using 300s and 600s and wondered if longer subs would be of benefit.  Your input suggests that this would not be the case as more noise and saturation would be the result. I will therefore stick with 600s maximum.

Good point about longer subs in out weather environment. Losing longer subs to a passing cloud is so frustrating.

Thanks again