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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 16 Aug 2010 (Monday) 02:59
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Very First Attempt: Night Sky

 
jwcdds
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Aug 16, 2010 02:59 |  #1

I tried my hand at some astrophotography tonight. Certainly less-than-ideal situation (as I'm in the city and talk about light pollution) :lol: Takes a lot of tweaking to even get something remotely acceptable.

4s, f/1.4, is1600, 24mm. (And a whole-lotta-levels tweaking in CS5.)

IMAGE: http://julianchen.smugmug.com/Photography/Astrophotography/201008157565/971402815_wEE54-XL.jpg

I don't know how you more experienced folks do it. I see some people say start with iso1600, f/1.4, and 20s. All I got was nothing but a white, blown-out image. :lol: I need to get out of the city I suppose.

Would've been nice if I had something on the horizon for reference/composition but I was just gunning to capture some stars tonight. This will be a VERY LOONG work-in-progress for me. But I'm eager to learn. :)

Julian
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jsigone
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Aug 16, 2010 10:46 |  #2

Good start. But you can't really shoot at wide open like that or you'll get allot of curvature in the lens like you did having all the corners blacked out. Generally you need to go 1 to 2 stops down from wide open to flatten out the field/lens. With that lens I'd probably start at F2.8 and see how the corners are. Go up another 1/2s stop and see if the corners don't improve. If they do try another 1/2stop up. You're trying to find the sweet spot of the lens. It could be F2.8 or lower.

If you have allot of light pollution, you can also try to set the CWB on the sky background and see if that helps, You can always change it later on the PC as long as you're shooting raw. If you're using a fixed tripod and the 24mm, you can probably push 20-30 sec subs before you see tailing unless your pixel peeping at 100-200% crop. At that you're not taking the image for whats its worth.

Another trick of the trade is to stack multiple images to bring out the details. Let say you take 30 subs, you ideally want 30-50 % more subs with the lens cap on, these are called darks and when you stack them will cancel the noise out. Deep Sky stacker is a free and easy software to do that.
Here's a good tutorial I found on both DSS and basic PS leveling and curve changes.
http://astrochat.co.uk​/forum/viewtopic.php?t​=13241 (external link)

Enjoy the process and don't be scared to try things, the 7D is turning out to be a great camera for AP, very sensitive sensor and should catch allot of Ha (red) nubulas w/o modding it.


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jwcdds
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Aug 16, 2010 11:22 |  #3

Excellent! Thanks for the tips. I'll look into the DSS tutorial.

On one of my attempts to tweak the photo, I went into "curves" and used the dropper to sample image to set black point. Made everything dark, but also took away what I believe are the fainter stars. We'll see. I'll start w/ f/2.8 and also try to find less light pollution. :D


Julian
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jsigone
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Aug 16, 2010 12:42 |  #4

Here's another link to help you better understand setting black & white points and where to adjust them in the curve. http://myastroimages.c​om …_To_Use_PhotoSh​op_Curves/ (external link)

But first you need to color balance the histogram using the level slider per color channel. Once RBG is line up you can start to pull the curves to bring out the details without messing up the color balance. Some times it's easier to crop out the center and work from that, that way you're not getting all the black in the histogram from Vignetting.


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SteveInNZ
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Aug 16, 2010 14:22 |  #5

Search out some gradient removal techniques for astronomical images. They're easy and your image should respond well to them. Then you can start on the curves/levels to drag out what's in there.

Steve.


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Very First Attempt: Night Sky
FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
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