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How to fix purple stars?

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#1 Jeff2011

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Posted 08 January 2013 - 02:47 AM

While I was at a dark site in December, I took some shots with my DSLR (35MM lens) on an EQ platform. Attached is a 137 sec, 400 ISO unprocessed (except sized down) shot with Cassiopeia at the top. Cass's stars have a purple halo. What is the best way to correct this? For processing software I have, Digital Photo Pro (from Canon), gimp and IRIS.

Thanks,

Jeff

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#2 Bill W.

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Posted 08 January 2013 - 08:07 AM

If you have Adobe Photoshop there are actions from Noel Carboni to fix halos. His web site is at

http://www.prodigita...ll_Version.html

-Bill

#3 ky1duck

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Posted 08 January 2013 - 10:39 AM

i gave it a try using the above stated astronomy tool is Photoshop.all i did was light polution remove and halo remove

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#4 Jeff2011

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Posted 08 January 2013 - 12:38 PM

Awesome utility. Guess I will have to spring for PS. I am just starting out and currently using Gimp. Looks like those utilities only work with PS. Using my tools I was able to adjust the hue to change the purple to blue but halos were still there. I assume there is a brute force way of doing it, but I like the ease of the utility.

#5 TimN

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Posted 08 January 2013 - 05:31 PM

I think there are now better alternatives for AP than Photoshop. Photoshop isn't easy to learn, is expensive and wasn't made for astronomy so plug-ins are required. I would look at Pixinsight and StarTools. Both of these are significantly cheaper than photoshop and were made by astrophotographers for AP.

However, if you are thinking of trying Photoshop I would recommend you pick up CS2. Its currently FREE - legally. http://gizmodo.com/5...free-right-here

#6 Jeff2011

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Posted 08 January 2013 - 07:41 PM

Thanks Tim. I had seen StarTools mentioned on another thread and I have been looking into it. I am not too keen on shelling out big bucks for PS and only use a fraction of its capabilities. I learned a lot playing around with Gimp but its definitely not easy. My understanding is that these programs are for finishing the picture. I would still need to use IRIS or DeepSkyStacker to align and stack the frames prior to using StarTools or PixInSight. I am currently using Jim Solomon's cookbook as a work flow for my DSLR DSO processing but it is a bit dated. Are there any other recommended work flows that I can learn from?

Jeff

#7 jrcrilly

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Posted 08 January 2013 - 07:46 PM

Rather than buying software, you could just choke that lens down a couple of F stops to where it will work better and keep the light focused. Wide open, they have trouble with fiddly objects like stars.

#8 Jeff2011

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Posted 08 January 2013 - 08:45 PM

Good suggestion John. I was so used to the fixed f stop when attached to my telescope that I forgot that I could change it with the camera lens. I did have it wide open at f2. This was just a test shot I took while at a fairly dark site. Did not have much time for AP since I had planned to do mostly visual. It will probably be a while until I can get back to a dark site again. Anyway, I have learned a lot from this post. Thanks for all of your responses.

#9 TimN

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Posted 08 January 2013 - 11:15 PM

Jeff, in terms of workflows I assume it would depend on what software you use. I use DeepSkyStacker to align and stack the images including any darks and flats. I used the documentation that is available on the DSS site. I started just using the recommendations provided by DSS. However, I do not use DSS for any processing. I save the file from DSS and load it into StarTools. Again, I used the tutorials available on the StarTools site.

DSS is free and StarTools is also free to try. If you decide you like it its only $60. So, if you want to try them there isn't much expense involved. Each of these programs have their own site if you have problems or you can always ask here on CN. The people here are great and have helped me a lot.

#10 JoseBorrero

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Posted 08 January 2013 - 11:26 PM

a yellow filter work. cant remember the number

#11 Jeff2011

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Posted 09 January 2013 - 11:45 AM

Tim,

That is exactly the route I was planning on taking. Thanks for the reassurance on going in that direction.

I saved off my Orion nebula raw frames that I had previously processed with IRIS and plan to use them as a test/comparison. I studied the docs for DSS and the tutorials for StarTools last night and together they look like a very streamlined process. IRIS is a powerful tool but too complicated for a beginner like me especially if I wander off of Jim's cookbook script.

The main thing I struggled with IRIS was the image registration. Because I am using a home built EQ tracking platform there is some tracking error and I have to limit the light frame exposures to 5 seconds or less. I had to diddle with the IRIS settings to get them to register. I expect to run into the same with DSS. Right now my goal is to learn the techniques of DSO AP with the equipment I have. After achieving a certain level of proficiency, I plan to upgrade my equipment.

Thanks

Jeff






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