In regards to noise I wonder if someone can explain what I'm seeing in this 29C dark frame from a modded 40D. What are the brighter reds, blues and greens? Also there is the odd white spot (see close up). More subs and dithering seems to reduce it all so not concerned, just curious.
Its probably just dark noise. Not sure but I think you take dark flats to reduce the effect.
"Additional electrons will be generated within the CCD not by the absorption of photons (i.e the signal) but by physical processes within the CCD itself. The number of electrons generated in a second will be dependent on the operating temperature of the CCD and hence this noise is known as thermal noise (sometimes also known as dark noise)."
They're hot pixels. Pixels that are a lot brighter tan the pixels around them, sometimes CONSIDERABLY brighter.
The reason for all of the different colours is that some are under red filter, others green and yet others blue.
In a mono sensor (not bayered) it is just brighter pixels scattered throughout the image.
Thanks for that. One of those things I've assumed but never really known. Dark flats I'll look into, although I have just been calibrating with darks and flats (with the bias removed from the flats).
If you're just using a DSLR and your flats are less than 1 second (mine are usually 1/100th of a second) then a bias frame is perfectly fine. Flat Darks are mostly useful when doing narrowband flats and you're taking 5-20 second flats.
While we're on the subject of dark frames, in comparison my darks are blacker than Benjamin's. Is this a modded camera thing or just a difference between camera sensors? Or is that stretched to show the hot pixels better?
Here's one of my darks, 120 sec x iso 3200, canon 1100d unmodded
Yes the dark was stretched and debayered. I've attached an un-debayered, unstretched dark which shows that there is still a nice 'star-field' of noise!
