Bias Frames

[jgs001]

Since Martin posted his tutorial on Bias frames, I've been using them during the stacking process. This is on my last three deep sky images. Something that really puzzles me, why am I getting a green tinge to all my images after stacking that I have to then process out ? Any one have any ideas ?

[blinky]

Do you use a light pollution filter?

[jgs001]

A skywatcher LP filter Craig, but that gives a pink cast to each frame. And the green cast appears if I apply Bias frames. When I didn't apply Bias frames, this didn't happen. I'm going restack my M67 without them and see what happens.

[steppenwolf]

John, are you BIAS subtracting before or after you have de-Bayered your images?

[jgs001]

I'm letting DSS do it Steve, I wouldn't know how to do a Bias subtract anyway... I load up the lights, darks, flats and bias frames and click go.

[steppenwolf]

I load up the lights, darks, flats and bias frames and click go.

I wish my life was that simple Are you taking RAW or .JPG images?

[jgs001]

RAWs, I only now take jpegs by accident , as in taking the camera out the bag I've knocked the mode dial and not noticed

[jgs001]

I've posted up the restackin my original thread here

[jgs001]

Ok, progress of sorts... I've tried a stack without the bias, and that's got the colour sorted out. I've tried a stack without bias but with the black point set to zero and it's gone green again. I've tried a stack with bias and not setting the black point to zero and the DSO has not appeared in the resulting image.

[Reggie]

I thought setting the black point to zero in dss was for modded cameras?

[jgs001]

Based on the info in DSS, and the DSS Yahoo group, if you use Bias frames you have to set the black point to 0, for any camera. I ran a stack with bias frames and not setting that, and only the brightest stars showed up in the result, no matter how far the image was stretched. I tried this on my triplet image, and there was no sign of the galaxies.

[jgs001]

Ok, I think I have this sussed now... It was a combination of setting the black point to 0 and letting DSS auto set the white balance... The green is now gone. What I do need to do is work out how to do a custom white balance shot at night...