Total "Lights" time?

[iceman]

While i'm on a roll asking fundamental DSO imaging questions.. :)

With an unmodded DSLR, is there such a thing as an "ideal" total length of time for your lights?

Most people seem to do between 60-90 minutes of "lights" time - is that just because any longer and you need to start thinking about meridian flips, or is there some deeper reason why you don't keep imaging the same object all night long and getting 2-3 hours or more of "light" time?

Surely the longer total lights means less noise and potentially more signal, a smoother image that can withstand more stretching etc..?

Thoughts?

[turbo_pascale]

Plenty of people do "mega exposure" images, over several nights.

See some of the efforts of Brad Moore, Fred Vanderhaven etc (14-15 hour exposures etc), not to mention Rob Gendler who has cracked out some ridiculously long exposures..

Edit: But all these guys are using SBIG cams! not unmodded DSLRs.
In the end, the more data, the less noise. Go long.....


Turbo

[seeker372011]

well Mike the longest i have gone is 4 hours-mainly because I have about an hour or more of darks to take after that and i am getting tired by that time..if I don't get at least two or three hours on a target I am not usually satisfied with my results-too much noise especially my 300D

[Dennis]

Yeah - 3 or 4 hours really gets some nice data, especially on the fainter objects such as M83, M16, NGC6744, NGC1365, etc.

Cheers

Dennis

[[1ponders]]

Definately go for longer total times. I believe that part of the reason you find people (well me anyway :) )only taken shorter total times is that they are trying to get as many images in on a night as possible. If you check I think you will find a direct correlation between the longer someone has a DSLR and the fewer different objects they try to image in a night. We soon wake up to the fact that longer is better.

JMO ;)

[Geoff45]

I agree with the comments above, there's no such thing as too much exposure. However, remember that noise goes down as the square root of the number of subs. Going from 20 to 80 subs halves the noise--going to 160 only reduces by a further 1.4 times. The law of diminishing returns.
Geoff

[vash]

I prefer to image just one images a night and maybe experiment with another, mind you, haven't been out since october.

[RB]

The longer you image the better it is Mike, but the length of the subs depends on your sky conditions.

I've always wanted to do a few hours on an object but unfortunately I haven't got guiding underway yet and between work/family and the weather it's been a long time between drinks.

Ideally if you setup early and the weather holds out, I would concentrate on one or two objects per session, to include darks as well.