View Full Version : Comet Garradd

2011-Sep-02, 01:50 AM
I'm late with this one. Processing it gave me fits. Normally I find it easy to remove the stars with a data rejection stacking once the images are aligned on the comet's core. I found that impossible due to the dense star background. Getting rid of the comet is easy with a gradient tool and a bit of cloning out what little remains. I finally got rid of the stars in the luminance frame but the color frame was far more difficult. After days of swearing I finally managed it. I'm now way behind on my normal processing backlog.

I debated on how to handle the ton of stars seen through the comet's tail. I ended up blocking the vast majority of the faint ones. Just detracted too much from the comet. So only the brighter were allowed to show with the fainter ones masked out in the star field image.

This one seems to be a case of too much aperture picking up too many stars.

Comet's color wasn't nearly as strong as on some other posted images. Probably needed more color but the clouds had other ideas unfortunately.

All those stars made for a larger file than I'd like but when I lowered the compression the comet didn't fair very well. It's way too big for the limits here so see the link below.

14" LX200R @ f/10, L=30x1' RGB=10x1', STL-11000XM, Paramount ME



2011-Sep-05, 11:26 PM
Rick if I can suggest something - you cut too much background. Night sky isn't that dark. If you are using PS try to set background around value 20 - more less. It'll be much more natural.

2011-Sep-06, 07:11 AM
Yes it is dark. I did that on purpose. To get rid of the remains of all the stars all rejection routines I tried failed to do I had to blur them out with a motion blur which went down the tail. This created tail that wasn't real. Setting it dark left only what I was certain was real comet tail detail. What can be brought out brightening it is questionable so I kept it hidden.

I set my monitor so even a level of 4 is not dark and easily shows the difference from 0. Yet I can separate 251 from 255. Not all take the time to do this or have monitors that can't do it. To me 20 is darned bright and limits the object's range to fewer levels than does a background of 10. Bad enough shoehorning in the 4000 or so levels a typical CCD can reliably show into 255 levels. I don't like to give up any I don't have to. But I realize some won't see the faintest detail.


2011-Sep-06, 11:32 AM
"This one seems to be a case of too much aperture picking up too many stars."

Well, the comet is crossing the Milky Way now. The tail was better back in Pegasus, the fork was easily seen then.

This comet has shown me why Messier made his catalog, I used to think how could someone confuse a comet with a nebula. I hope that once Garradd encounters the Sun that the view is much better on the outward journey.

2011-Sep-07, 02:52 AM
Hi Rick, Still a Beaut!. I tried to use the methods and gave up maybe later on will give it a try again.