Nebulosity or Imperfections?

[Astrosurf]

I've taken two images of the Leo Triplet, one with a modded DSLR and the other with my Atik on Luminance. Both have patchy background, which I managed to remove from the colour image as it was reddish. I can't with the luminance one. Is this nebulosity or imperfections in capture and processing?  I used StarTools and Photoshop for the processing. I also need help with processing as I'm awful at it!

[vlaiv]

It looks like artifacts. I just compared this image with a couple of images found online, and those images while displaying tidal tail of Hamburger (meaning they are quite deep) show no such nebulosity.

Might be a problem with star tools and erase background command, but I can't be sure about that.

[happy-kat]

There are excellent StarTools articles on how each function works and when you would use it on the Startools forum plus there is the unofficial pdf user guide.

[Astrosurf]

Thank you. I didn't use any erase background command. Do you know what I can do to rectify the problem?

[happy-kat]

How much data was in your image and where there any flats and dark flats?

[Astrosurf]

4 minutes ago, happy-kat said:

e excellent StarTools articles on how each function works and when you would use it on the Startools forum plus there is the unofficial pdf user guide.

Thank you. I've yet to find the time to read them!

[Astrosurf]

1 minute ago, happy-kat said:

How much data was in your image and where there any flats and dark flats?

No flats or darks. The camera was cooled. I try to cram in as much data as possible. Flats take too long! But I think the problem is with my Atik so I might need to start doing them. 6 x 10 mins, 3 x 15 mins and one x 30 mins, trying out different exposures. All group stacked in DSS - default settings. Here's a quick and  dirty stretch - yuk!

 

[Astrosurf]

Here's a deliberately blown-out canon image. The patchiness does seem rather similar.

 

[happy-kat]

If using Startools there is a preferred method of DSS stacking. Don't align rgb. It's been covered on a couple posts I don't have the link to hand.

That's very patchy, I'd want to understand what was making those patches. Are they worse on your 15 minute sub?

[vlaiv]

I think that key is in the following part of sentence: "No flats or darks" ....

Patches in stretched lum image look like dust far away from sensor (bunch of circles approximately same diameter).

[Astrosurf]

Ta, I don't do any alignment in DSS. Just save file with embed adjustments etc. Here are the unstretched 30 min and one 15 min file from FITS. The 15 min has the satellite pass.

[happy-kat]

Flats and dark flats don't take a long time (darks do). 

[happy-kat]

StarTools prefers the autosaved fits file.

[Astrosurf]

I'm a bit daunted by flats with all the light source malarkey! I'll have a go.

[Astrosurf]

Just now, happy-kat said:

StarTools prefers the autosaved fits file.

I've tried processing with FITS and I never get a good image.

[Hicks]

There's nothing to lose by trying a few different methods of taking flats. Worst case you waste 5-10 minutes at the end of a night trying different methods and finding none of them were of any use and you're back to where you are now. Best case, you get rid of any vignetting and dust for little to no effort

Lots of ways to try to take flats. If you're still setup near morning, just taking images of a blank part of the sky (rogue stars can be removed in post), or with a tshirt over the scope, or a laptop/tablet with a white screen. There's more ideal options too, especially if you want a good illumination across different filters, but I'd at least give laptop/tablet a go rather than no flats at all. Once you have a suitable light source it takes a couple of minutes to get a hundred frames.

For bias and darks, if your camera is cooled, you can always take those after setup whilst you're waiting for it to get dark enough to start. Unlike flats you can also just take them the day before/after or inside as long as the camera can be cooled to the same temperature.

Worth doing and seeing if it makes your life easier in post processing.