How noisy should a DSLR image be

[TrevorW]

This has been bothering me in the sense that without feedback I cannot tell whether or not my camera's sensor is noisier than usual or faulty.

With longer exposures I get considerable noise the image often looks washed out and nothing like what you see through the scope, naturally I'm aware of the problem of noise is CCD camera's etc but how noisy should the image appear.

Also I've noticed dark lines appearing at either the top, sides and or bottoms of the images the longer exposure you take, is this normal??

:help:

[bojan]

Individual shot may be quite noisy... the noise level will be affected by temperature as well (warmer the camera sensor, higher the noise, and the dependency is exponential with the temperature)..
But it should be averaged out in stacking process.
"banding" (this is caused by camera circuitry) is also supposed to be random, so it should average out (so that means, more sub-frames, the better... 10-15 sub-frames should ne adequate, though).

EDIT:
Have a look at this:
http://www.iceinspace.com.au/forum/showthread.php?t=37039
this was taken with Canon 400D at ISO 1600.

[dannat]

trevor what ISO levels are you shooting with the noise?,
do you have problems at low ISo?100

what type of camera is it?

[TrevorW]

I are only shooting at ISO800 for astro images, haven't tied longer expsoures at the ISO200 which is the lowest setting on the camera which is a Pentax K100D 6 mp

Cheers

[dannat]

you could try iso 400 & compare wth 800 - phil hart said cameras can differ a bit and 400 might be all you can push some without too much noise

[Geoff45]

How long are the exposures? Could you post some pics?

[Lester]

Noise levels will vary from model to model. eg. the Canon 400D produces a lot more noise than the 20D at the same temperature and iso.

Sorry I cannot comment on the Pentax for noise amounts. Ambient temperatures below 10 degrees have minimal noise, but at 15 degrees it increases a lot, with my experience.

[TrevorW]

Could be an issue on warm nights then as last night in Perth it was well over 15 degrees. Anyone have an effective cheap way of cooling a DSLR for those summer night imaging sessions.

[dugnsuz]

Agree with that, I've been trying iso1600 on the 40D with acceptable results (to my eyes anyway).

Experiment Trevor!
:thumbsup:

[dugnsuz]

ps...Yep, my iso1600 successes were in the cold!