[Slawomir (Suavi)]

Very interesting discussion.

I tried to follow Rick’s instructions to measure SNR in a 2.5 hour test image of NGC 6744 taken from Paddington.
I measured mean background signal in a few featureless areas in the image and subtracted it from mean signal in a bright, medium and dim areas of the galaxy. Then I multiplied the resulting ADU values by gain so that in theory (I hope) should give me the number of photons in a 2.5 hour stack. Signal is still quite dim in 2.5hr exposure; it was only 27 photons in the bright area, 16 photons in medium-bright and only 1.4 photons in the dimmest parts that I could recognise, giving me SNR of 5, 4 and 1.2 respectively. I need more exposure!
Is the above workflow correct?
Suavi

A link to the image in question (although this stack had a touch of noise reduction applied): http://www.astrobin.com/full/305157/C/?nc=user

It clearly looks very noisy…