|
I have done a bit of testing and I'm unsure about these results. The raw sub is a 12 min OIII. I took 50 bias frames, 20 x 12 min darks, and 30 flats. Perhaps with more frames I wouldn't see such a big hit to the s/n.
The s/n seems to really suffer if I subtract either a dark or a bias. If I apply just the flat without a dark or bias the flat does not work properly though the s/n is only reduced a little. I tried making a flat without subtracting the bias and it also doesn't work properly. Here are the s/n. (Are these values in line with what you see with your Trius type camera?)
Raw Frame s/n = 2.61
Flat calibratio only 2.45
Bias only .43
Dark only .38
Bias + Dark .38
Dark + Bias + Flat .39
Bias + Flat .43
Are the benefits of applying bias or dark worth the price of the s/n reduction?
I must apply a flat. However I cannot apply the flat master without a bias or dark subtraction. Is there a reason why this isn't working? My flats were made at ca 35,000 adu
There is one other odd (?) thing I don't understand. In the info window that also measures s/n the raw image shows a range of ADU values min= 1330, max = 64999. After applying a bias: min= 76, max = 63733. After the dark frame: min= -14,664, max 63,705. I'm not sure what the negative number means....
Thanks for any help!
Peter
Edit: I started this thread thinking it was going to be a software question about using CCDStack. It has clearly turned into a more general processing question. Should I move the thread?
|