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Complex Vignetting Removal with Star Tools

brent1123
20 Sep, 2016 18:15
I have been working on capturing data for the Eagle Nebula. My data was taken over 2 nights so far, but I neglected to ensure the camera was placed at close to the same angle during these nights - while I took Flats before removing the camera from the scope each time, this still caused noticeable lines and vignetting when stacking the two sets together. I am using Star Tools to process my stacked images (from Deep Sky Stacker), and though I have experience removing Vignetting on typical images, this one is more complicated than I am used to. Would I need to use another program like Photoshop or Lightroom to remove most of this?

I also plan on adding more Lights this and next weekend, would adding Lights with an angle in-between the 2 in the image (below) smooth out the differences?
 M16 Stacked - dotted lines marking the 2 angles
1074j
21 Sep, 2016 18:24
Wow, that image is a mess.  You are right, I don't think Startools is going to be able to fix that.  I would crop out as much around the edges as you can, then try Vignetting removal again.  At some point, you might have to give up and retake the data.
M
1074j
21 Sep, 2016 18:27
I see you have equipment similar to what I had when I started-450d and a 8SE.  I never did get great images with the Canon and soon invested in a ccd camera and filters.  It was time well spent learning the ropes of imaging and processing though.
Mike
brent1123
21 Sep, 2016 19:02
Some of the color splotching is from the fact that I had pixel correction turned off in DSS - hot pixel correction was turning my stars into rings, but I'll have to reactivate cold pixel correction and see if it improves image quality. Each night of data by itself presents an alright image - I really have little qualms in trashing one night of data, M16 sets a little after midnight anyway, so its not like I wasted 6 hours on it. I do plan on adding more in the next weekend or two before the Milky Way realy starts to set too early, so it should still turn out alright.

Are CCD's typically better than DSLR's given a comparable price? I like having a DSLR since I can possibly do wide-ish fields(if I spend more on lenses), or use it for daytime. I started out using a ZWO ASI120MC for planetary, but I've been focusing on DSO's with the DSLR since April, and especially after June when I bought the CG5. My best attempts, even with Drift Alignment, has been 120" in Cassiopeia, and 90" for equatorial objects (37 N here). I have not yet tried autoguiding - would you recommend an off-axis guider? I have received advice from others that a separate guide scope would not help much considering that even with a reducer I am imaging at f/6.3 - I do plan on getting a fast Newtonian or perhaps a small refractor, but that is months ahead of now.
1074j
21 Sep, 2016 19:41
The 8SE can make some good images-I still use mine occasionally.  A high-quality small refractor is a good second imaging scope. (I have a AT 80EDT)  The new ZWO ASI1600 would be a great cooled mono entry as it's a big CMOS sensor that is as sensitive as a CCD and about 1/2 the cost and very very low read noise (thus you can take lots of short subs).  In fact, I'm thinking hard about one myself.  Comes in color too if you don't want to invest in filters and color wheel and I've been considering that to simplify imaging as I just don't get enough time under the stars. (who does?)  I think you were located in Tulsa thus you have some amount of light pollution to battle with.  A mono camera with a Ha filter can really work some magic.  This was shot from a suburban sky in Tucson.  The Ha image is also included.
http://www.astrobin.com/127027/B/

This is no longer a problem now as I have a cabin in the mountains in far SE Arizona with completely dark skies-Bortle 1-2 and I do all my imaging from there now.

For short focal lengths, a separate guide scope is fine, otherwise, go with OAG.  You can use the 120 for guiding thus you don't need another guiding camera.  Plus short focal lengths are more forgiving especially if not using guiding.  I alway guide thus don't worry too much about exact polar alignment.

It's my opinion that you won't get really good images with the 450d as it's too noisy and no cooling, but  your M27 is still pretty good.   Also, I try to take all my subs in one night in order to keep everything the same (FOV, optical train, transparency, alignment) thus you shouldn't have problems like you had.   Pick your object with this in mind and remember there is always next year.

I've been using Startools for years as it was cheap compared  PI and easier to learn.   I like it except the noise reduction has some issues. (or I'm still not using it right)  Note the noise in my most recent image of M94.
http://www.astrobin.com/264973/
Good luck!
Mike
1074j
21 Sep, 2016 20:59
I take back what I said about the 450d not being to make great images.
http://www.astrobin.com/full/262722/0/
 
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