rings around my galaxy :O(

[Moon monkey]

Hi everyone I could do with some advice please .... Last night I took 245 75 sec pictures of M31 ... I have used DSS to stack them and add 30 darks, and then CS5 to stretch them... once they are stacked and stretched even a little I get all these ring things around the image ??? I can get a better picture using just one frame !!! Any help please .....

Canon 550d modded ....800iso no LP filter.

Cheers MM

Single stretched sub...

Stacked image and stretched a little ...

[VigdisVZ]

I think I know what you mean.

I think you need to work more in post processing, also it may be caused by using too shallow color depth. It can also be an artifact generated when you're moving the picture between programs or even when saving it.

[Daniel-K]

Chas was there any filters on at all?

[VigdisVZ]

Oh, did you stack the RAW? Stacking JPG would create a much worse result.

[Moon monkey]

Hi Dan no filters ....

And stacked in RAW ...

[VigdisVZ]

Ok... I cannot really help you out here, but I've encounterd similar artifacts when working with other types of images. Hopefully someone more experienced should be able to chime in. In the meantime, try stretching and mixing the processing sliders in DSS some more, intuition tells me you should be able to coax a lot more out of it. It's jus the matter of finding that right setting, that can be very elusive sometimes.

[rfdesigner]

Asking a dumb question..

you did remove the dark, then align, then stack didn't you?, and you kept it in at least 16bits for each step.

Also check your subs.. one really bright sub because of a neighbours skyglow generator could give you some problems, shouldn't give contours, but it all depends on how the maths works.. a sigma clip stack would sort out a bad sub.

Derek

[Moon monkey]

yes Derek Dss subtracted the darks and went through all the usual stuff .... Subs all look identical ... no bright ones...

[Rezn8]

I found importing raw into photoshop,saving as tif/fts then stacking improves final pic.

[Rustysplit]

I have had this problem and found it to be an issue with flats. If my flats were too dark or non existent, I sometimes got those exact same rings.