Darks do not get rid of amp glow...

JohnH · #1 19-07-2007, 03:41 PM

I have been able to guide better recently - allowing me to go for longer exposures and reduce the ISO rating on my DSLR from 1600 to 800 to get better dynamic range....

Now I have noticed that with exposures in the 200-300s range I find amp glow present in my images even after dark frame subtraction.

Why would this be?

avandonk · #2 19-07-2007, 04:16 PM

Try the in camera noise reduction as it gets rid of amp glow!

Bert

JohnH · #3 19-07-2007, 04:55 PM

Hmm, I thought I was better of with darks...that way I can collect more lights...I'll try in in camera routine for a comparison...

avandonk · #4 20-07-2007, 10:28 AM

Unless you can get darks at exactly the same temperature you will always have amp glow and more noise after subtracting darks. The problem is the camera temperature varies with ambient and you will also notice the first exposure with ICNR has 'dark holes' as the camera sensor is actually warmed up during the first exposure. A camera at idle is cooler than a camera taking a long exposure. I have found that it is better to use ICNR than any darks.

If you could keep the camera temp constant then darks would work almost as well ICNR. I am sure it would never be better as Canon do some very cunning process at the individual pixel level. I have tried using all image files in the original Bayer CFA in Images Plus for dark subtraction flats and bias and it was not as good as ICNR.

Bert