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Orion Widefield

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#1 laidman

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Posted 05 January 2013 - 04:55 AM

Hey folks,
This is my first real attempt at post-processing. Stacked in DSS, then Photoshop.
Canon 40D, ISO 400, f/4, 75 seconds - stack of 120 images
I'm still really disappointed with the colour gradients and the colours in the final image.
The first time I stacked them I included the flats I'd taken, but ended up with a much darker patch halfway up the left side of the frame, so I stacked them again and ended up with what you see here.
Shouldn't flats take care of problems like vignetting, etc.? Or are they more to just eliminate dust spots in telescopes? (There's also a very good chance I didn't do them correctly - it was my first set of flats).
This was taken on a pretty dark, moonless night where I live. Without a sky pollution filter in this the best I can hope to do in terms of H-alpha? You can just start to see Barnard's Loop coming through. It would probbaly be easier to see without all the terrible and funky darks/lights/funky colours...

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#2 cherokawa

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Posted 05 January 2013 - 03:22 PM

Looks like you have some pretty good data in your image. The gradient to the left looks to be from light pollution and this is not something that flats can fix - something like Gradient Xterminator with PS helps a lot in removing some of these gradients. The orange at the top-right corner might be caused by amp-glow, not very sure though.

I ran your jpeg through a couple of rough runs of Gradient Xterminator and you can see the results below. I'm sure a more careful processing can provide much better results. I'd say you have an excellent image there, especially considering the sub lengths and integration time.

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#3 laidman

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Posted 07 January 2013 - 06:26 PM

Thanks Cherokawa.
I downloaded the GradinetXTerminator Trial and it seems to do a pretty good job. It really sucks the contrast out of the image, though, so after doing it it seems that another curves/levels adjustment is needed.
I'm just starting to get my head around some of the things that can be done to pull information out of the muck. One thing I'm curious about is how you know when you've pulled out all the detail that is possible/practical without introducing a bunch of noise and other unwanted artifacts.
For example, in this shot you can start to see Barnard's Loop and the Witch Head, but since this is an unmodified DSLR they are both very faint. If I try to pull more detail out then the image gets both too bright and too busy (too many stars with too little seperation). Is there any way of knowing roughly how much you should adjust the levels/curves before admitting you're not going to get any more useful information out of the image (like any increased faint detail means a brighter, noisier image)?
Cheers,
Mike

#4 NeilMac

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Posted 08 January 2013 - 12:52 PM

Very nice!

#5 JoLo

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Posted 08 January 2013 - 01:33 PM

Ahh, you have identified the great conundrum of AP...signal vs. noise, it all comes down to that. You will not want to hear this overused gem either, but each image is truly different. So many variables go into how the picture turns out...light pollution, temperature, equipment, guiding, atmosphere that night...that each one needs to be assessed on its own merits.

It will come with experience, and you will know when you have a deep, clean image that can be stretched to reveal detail, or a noisy mess that will only give up so much. The other night I was out in the upper 20's getting 3 hours on the Orion Neb with an unmodded Canon...everything was clicking on a clear, crisp night and I ended up with virtually no noise on my stacked image. This summer I had three hours on the Veil on a clear, but much warmer night and some guiding issues. The noise limited what I could do with it. Another overused AP cliche, but no less true: everything is a tradeoff.

You just get a feel for it after a couple years of doing it. Experiment with GXT, use masks with it, play around...great tool. I use an inverted object mask with it to isolate the background and keep the goodies out of its xtermintation routine. Patience, young Skywalker.

#6 Orion_PKFD

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Posted 08 January 2013 - 01:51 PM

Awesome!

#7 laidman

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Posted 08 January 2013 - 07:37 PM

Thanks everyone!
JoLo - I guess if it was a straightforward, set routine then everyone would be doing it! Thanks for the tips. I'm off to check out inverted masks...

#8 JoLo

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Posted 09 January 2013 - 11:28 AM

Oh, how right you are......

Here is how I do inverted object masks for gradients, works with any process you want to do on a background, or stars/nebula/galaxies if you don't invert the mask. Widefields like yours have more gradients to deal with..this method works well with nebula and galaxies in a smaller FOV as well.

1) Duplicate the layer
2) Add a reveal all mask to the duplicate
3) Select all and copy original layer
4) Alt + Click on the mask...this will show the mask in PS
5) Copy the image to the mask
6) You now have a greyscale version of your image on the mask, select Image/Adjustments/Invert
7) The stars / nebula are now black (or grey), the backgroud is white....this is what you want (black conceals, white reveals)
8) Here is the tricky part...use CTRL + L to bring up the levels dialog. Move the black (left) marker to the right..stars/object get darker. Move the white (right) marker to the left..background gets whiter. You have to practice this step, you want to include all the white background you can, with stars and oject black / grey.
9) Click on the image on the new layer, run GradientXTerminator on that (important..don't run it on the mask, but on the image)

This will help control where GTX duzz its thang. You don't want your stars / objects included. The key really is fine tuning the levels adjustment, getting the background as white as you can without involving stars / object. Remember, the stars / objects don't need to be black, but do need to be grey at a minimum. If i can't get it right with levels, I use a brush set at about 20% opacity to paint in grey mask on the areas of the object still being exterminated.

Hope this helps, takes some practice.

Joe

#9 laidman

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Posted 10 January 2013 - 08:30 PM

Thanks for your detailed instructions, Joe.
That does look like it'll take some practice and fine tuning, but even on a quick run-through I could see the difference.

Mike

#10 JoLo

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Posted 11 January 2013 - 10:41 AM

No problem-oh, hope it helps. Yeah, it does make a difference and with a few run throughs you will be an inverted object mask whizz kid in no time.

#11 laidman

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Posted 11 January 2013 - 11:36 AM

Here's another go with some different flats and using your technique, Joe.
I was a little more aggressive with the noise reduction, and tried not too push it too much. I also used per channel background calibration instead of RGB in DeepSkyStacker, and it gave me much better colours.

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#12 bouffetout

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Posted 11 January 2013 - 05:16 PM

Awesome !

#13 laidman

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Posted 12 January 2013 - 12:04 AM

Thanks bouffetout!
I'much more pleased with the red nebulosity in this one. My inspiration for this image was from Dick Locke (http://www.dl-digita.../orion-wide.htm).
I know everyone has shot this area, but his was the first image I saw and went, "Whoa! All that's out there??"

On a side note I see in your sig that you;re using the CLS Astronomik clip-in filter. What do you think of it? Where I live now about half the sky is all light-poluted, and on the good half I've measured the skyfog at about 4mins to half-histogram as per here: http://www.pbase.com...37608572&exif=Y
Do you find it useful? Also, I'm only tracking with an Astrotrac, so whether I can expose long enough is another story... I can hit about 5 minutes at 200mm on a 40D, based on some subs I shot a while ago.
As I live on an island, a lot of the light pollution is due to squid boats which use (maybe) indandescent, mercury-vapour lights. (See picture)

On a much further side note, I see you're from Canada, and I'm assuming Quebec from your name. I'm from B.C. but went to school in Quebec, and now live in South Korea.

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#14 JoLo

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Posted 14 January 2013 - 11:38 AM

Looks great! A little playing with refining the mask and your can deal out that gradient and make your nebulosity stand out. Often times on a widefield I will play with the mask and do it 3 or 4 times, picking the one i like best. It is easy to xterminate some faint nebulosity, but just go back, refine the mask a bit, and run GTX again. Good job.

I occasionally use the CLS clip filter when I am imaging from home; my dark site is only 25 minutes away, so I go there when I can. At home, I have pretty good skies and can image about 10 meters outside my front door. I have LP to the south and west, and use the CLS clip when imaging in those directions. I try to image from about 50 to 90 degrees when the object is ascending in the east (I have trees below that....) and usually don't use the clip filter in this sweet spot.

In the south and west, however, the clip filter is a big help. Without the filter, I am washed out in one minute...with it, I can go 3 to 5 minutes per sub in these directions. It does leave a bluish-green cast on the images, but this is easily corrected in Photoshop. Depending on your particular LP, the Astronomik Clip filter comes highly recommended from this fella.

Joe

#15 laidman

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Posted 17 January 2013 - 03:18 AM

Joe,
Thanks for the info on the Astronomik filter. I've got lots of light polution to the North (which makes polar alignment more difficult than it needs to be...) from the city and hundreds of pesky squid boats! The Astronomik CLS filter is their basic light pollution filter, isn't it?

Just to clarify your GXT method a bit... After I've copied the photo to a new layer, added a reveal-all mask, and then pasted the image, inverted it and played with the levels, I then click on the regular colour image that I dublicated, right? I'm only wondering because the GXT effects seem quite subtle compared to running them on the regular image without the mask. (I'm completely new to Photoshop...Forgive me!...)

And if you choose a brush to paint in some grey you'll always be including a bit of the background, right? Since a lot of the nebulosity in my image is faint, especially towards the bottom, it'd be pretty hard to only select the red areas without getting a bit of background in there in between. But I guess that's OK....

Cheers,
Mike

#16 JoLo

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Posted 17 January 2013 - 04:28 PM

Yeah, it is very subtle, especially when painting on the duplicated image...I sometimes paint on the mask as well. I usually paste the image to the mask, adjust the levels, then run GTX. I assess how it looks, sometimes that is good enough and I leave it be. If some of the faint nebula "disappears", I use the history palette to go back before the GTX, do it again with less agressiveness on the levels. If gradients or color blotches remain (especially near the galaxy or nebula), I revert again using history (or Edit/Undo) and run GTX a little more aggressively and/or switching the paint brush to remove some of the mask near the nebula.

It's all trial and error and what looks good to you.

I also adjust the opacity to fine tune the mask, or when removing some of it. I usually keep it around 20% or 25%, so if you go too far, it is easy to fix. Just means if you need a darker mask, you go over the same spot two or three times, reclicking each time. Go in small strokes as well, so if you have to Edit/Undo, it doesn't taken down a lot of your work at once.

Yep Mike, you will always include some background or nebula when you don't want to...edit/undo, history, switching between black/white on the brush, changing opacity...these will help but it will never be perfect.

The good thing is, it is right, when you decide it is right. I play with it a few times, if it looks good, i call it a day and am happy.

Joe

#17 laidman

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Posted 21 January 2013 - 07:04 PM

Thank you for all of your posts, Joe. Very informative and very appreciated.






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