Quick DSLR imaging question

[Breakintheclouds]

I'm starting to make preparations for an attempt at some imaging with my Nikon D40. As part of this I just had a go at shooting a couple of dark frames, simply shooting 30s exposures with the lens cap on. The frames appear to be 100% black, with no hints of noise or hot pixels. I understood, from what I've read, that I should see some noise on the darks - after all, that's what they're for. Is what I'm seeing normal?

[Hawklord]

Have you looked at them at full resolution? When you magnify the image you should see that there are occasional red or blue pixels etc.

[lukebl]

In my limited experience, after only 30 seconds exposure you don't get that much noise. Try 4-5 minutes, THEN you might get some noise!

Regards,

Luke

[Dave]

Does your Nikon have auto substraction turned on?

If so it could be automatically taking an equivalent length dark frame and subtracting that from the image, resulting in what looks like a dark image. Unfortunately that will also degrade the image somewhat. I don't have any experience of using a D40, but my old D70 showed pink splodges around the edges from the electronics. My D300 has a very dark dark frame thankfully, so if yours shows a very un-noisy dark frame, without auto dark frame subtraction then you have a good camera there.

[Breakintheclouds]

Thanks for the quick replies all. I just did a 4-minute exposure and yes, there was plenty of noise! Good to clear that up.