One shot colour CCD quirk.

[ollypenrice]

Now that I have been using my OSC camera (Atik4000) for about 18 months I can confirm a slight oddity in the data once I have deBayered it in AstroArt. I wonder if anyone sees this or has an explanation?

Give the data a really big stretch and there is a curious colour gradient lurking in there. It runs diagonally across the chip, the triangle below the diagonal being slightly too red and the one above slightly too green.

Frequently it is so slight that no action is required in a real image but on other occasions it does need sorting. Pixinsight's DBE deals with it in a click so it isn't a problem. But how is it generated?

Olly

[roundycat]

Does it exist on a dark frame? If so it might be bias.

Dennis

[NickK]

I would look at a dark - if it's not present then it's something caused by photons (directly or indirectly).

Chromatic Aberation? However this would exist in flats rather than a star field and you've said it's a flat gradient rather than matching the starfield.

One option is the time it takes to read the chip. Usually they're read from one side, by draining each pixel in the row, then moving onto the next row down..

This would theoretically, given continuing star light, cause a trangular pattern.

[gbealnz]

Have you asked ATIK? Or posted on the SBIG forum (similar/same chip?).

Gary

[MartinB]

It is quite normal for there to be a gradient across a bias frame, something to do with the way the chip is read. If it's occurring after a bias subtraction then ? light impingement from a camera LED???

[ollypenrice]

I have never thought to debayer a dark till now. On the 5 minute one it is very slight. On the 10 minute one it is unmistakable along with a couple of things that look like stains on a coffee table from a cup. New set of darks coming on, I think!

I suspect that the 10 mn dark has a bad case of the phenomenon for some reason and is over correcting the lights.

Thanks for the tips.

Olly

[harry page]

Whats a dark then

Never used one in my life and not going to start now their importance in ccd cameras is vastly over stated

Harry