Noise Reduction Strategies

[James4]

Wonder what others think about noise reduction strategy.

I use a Nikon D5000 DSLR. I shoot in RAW with NR turned off.

I shoot darks at the end of my viewing/imaging session.

The other night I began shooting darks with camera still on scope. After the first two I thought, why not break down the scope and set the camera to take darks in the garage (just as freezing as outside).

Later when I compared the darks I found the ones in the garage - just the camera with lens cap on were much noiser than the two taken outside with the camera still on the scope. But also the two taken outside also differed from each other - one being quite a bit noiser than the other.

So now wondering if I should turn Long Exposure NR on in the Camera which will double my imaging time, but will give me dark subtracted light frames to process. Or will averaging a number of darks taken later work as well. I'm doubting the later strategy now after seeing how much the darks differ.

On a similar point, I shoot at high ISO - 6400 quite often. Is the noise generated at HIgh ISO random or uniform?

Any advice would be welcome.

Thanks, James

[jgs001]

My garage is a few degrees warmer than outside, and it's probably that, causing the darks to show more noise.

[vulcan]

Noise is random by definition. You will never get the same noise pattern twice. Using flats will not cancel out noise from the high amplification of 6400 ISO. The best you can expect it to do is minimise 'constant' defects such as dust and irregularities in the sensor (high pass filter). Noise reduction works best when it eliminates artefacts that are not constant over a period of time.