Help with CCD image

[traveller (Bo)]

Used my QHY8 for the first time last night.
25 x 3 mins of Tarantula Nebula with same amount of darks.
ED80 on EQ6 guided. Stacked and processed in Image Plus.
I overstretched the image to make the point and un-cropped. Several things are apparent
1. Vignetting around the image. I used Orion flattener for short refractors. It worked well with my DSLR but doesn't seen to do anything with my CCD Not sure why.
2. A few hot pixels, again, I don't get this when using my DSLR as darks take care of them. Again, not sure why CCD doesn't seem to minimise the hot pixels even with darks. Does that mean I need to do some biases?
3. Column defect/bleed on the right hand side (blue line running down) and a light green running on the left side. Again, do I need biases to eliminate that? It doesn't show with minimal stretching.
4. A few dust motes, I need to do flats.
5. The image is green and blue dominant, in big sections. Is this normal? Again, if I stretch gently, it doesn't show up as much.
Bottom line, I am pleased with my efforts, but would need to some advice on the image as to if this is a "normal" if overstretched.
Would it be worthwhile to have the CCD checked and serviced?
Thanks!
Bo

[vlazg (George)]

Bo, is the camera an osc, if so it looks like you have the incorrect bayer matrix.
Also , try dithering, it removes many artefacts.

[traveller (Bo)]

Originally Posted by vlazg

Bo, is the camera an osc, if so it looks like you have the incorrect bayer matrix.
Also , try dithering, it removes many artefacts.

Yes, its a OSC, how do I fix the bayer matrix?
Will try dithering.
Cheers
Bo

[Atmos (Colin)]

Originally Posted by traveller

Yes, its a OSC, how do I fix the bayer matrix?
Will try dithering.
Cheers
Bo

Different OSC cameras have different Bayer matrixes, could go:
RG
GB
Or different combinations, when DSS or other software debayer the image, f they use the wrong bayering method it can destroy your images colour.

[traveller (Bo)]

Thanks Colin and George,
I reprocessed using RGrGbB debayer and it seemed to have worked.
Still too much hot pixels I think
Bo

[Atmos (Colin)]

Originally Posted by traveller

Thanks Colin and George,
I reprocessed using RGrGbB debayer and it seemed to have worked.
Still too much hot pixels I think
Bo

Glad your colour is better
Hot pixels are easiest to get rid of with plenty of images and dithering so that the hot pixels aren't in the same spot on each image. If you combine as a Median or Sigma Clip it'll remove them.

[vlazg (George)]

Bo,
The stars are a bit eggy out to the edges, the qhy8 has a backfocus of 20mm and the flattener needs 55mm to the sensor. I think you need a 35mm spacer to get the correct distance.
The orion spacer ring kit from Bintel should do it.
George

[traveller (Bo)]

Thanks George,
I fished out a 35 mm extension tube and will try it out.
Bo

[traveller (Bo)]

Another try with processing (used Median when stacking as Colin suggested).
I should also add that I used a Baader UHC-s filter to combat light pollution.
Cheers
Bo

[Atmos (Colin)]

Originally Posted by traveller

Another try with processing (used Median when stacking as Colin suggested).
I should also add that I used a Baader UHC-s filter to combat light pollution.
Cheers
Bo

With 25 subs you are better off using a Sigma Clip of 2.5-3. Median stacks can be good but constrict the SNR that can be achieved. A sigma clip average combines the images and then removes anything that is x number of standard deviations from the normal.

[traveller (Bo)]

Thanks Colin,
I have a very steep learning curve ahead!
Bo

[Atmos (Colin)]

It is a never ending journey!