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Archive 2013 · Astrophotography White Balance
  
 
kodakeos
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p.1 #1 · p.1 #1 · Astrophotography White Balance


Hi

Hope this might be an easy one for ya'll

Im going to Glacier and Banff this summer and bringing my new star tracker with me to do some night shots of the stars, sometimes with the scenery behind it, some without...
But my last attempt at this in Grand Teton didnt work out so well, as I tried to light up the landscape with a little flash. Some experimentation worked out the manual exposure of the light and direction, but what I didnt notice was the WB change between the flash and the sky. I guess the sky is pretty high Kelvin, and the flash didnt not balance well. The foreground flash area would be correct, but the sky would be orange and looked wrong..
example: 3







I had to do a lot of gradient WB adjustment to get that right.

so my question is what K is the milky way, and what filter would I use on the flash to convert it to the right temp.




Jun 03, 2013 at 10:35 PM
ben egbert
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p.1 #2 · p.1 #2 · Astrophotography White Balance


This is the exact shot I had in mind for July except I would try to get the moon to light the barn. WB for star shots is tough even without the flash. I will be interested in what people say.

You have a great sky here.



Jun 03, 2013 at 10:51 PM
Matt Anderson
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p.1 #3 · p.1 #3 · Astrophotography White Balance


Simply gel the flash light or flash head, or fix it in post.


Jun 03, 2013 at 10:53 PM
JimFox
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p.1 #4 · p.1 #4 · Astrophotography White Balance


Yep, as Matt suggested, either use Gels, or change in Photoshop. You can use a warm filter on just the barn. Typically with shots like these, it's not uncommon at all to process the shot twice. Once with a WB selected for the stars, and then a second version with a WB for the ground layer, or in this case for the barn. Then just use a layer mask to put the two together, not too hard to do.

Jim



Jun 03, 2013 at 11:46 PM
 

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kodakeos
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p.1 #5 · p.1 #5 · Astrophotography White Balance


Thats basically what I did, The best flash exposure wasnt long enough to get the sky, so we did a 2nd exposure to get the sky. blended the 2 together and got that.
Problem was with some of them, the graduated didnt work out well, so I wanted to know what gel to get for the flash? do I need a blue gel or an orange gel? flash is 52-5500K, but Im unsure what the sky is, 8000,10000? Which would mean a blue filter right?



Jun 03, 2013 at 11:51 PM
kodakeos
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p.1 #6 · p.1 #6 · Astrophotography White Balance


Like this one, the graduated PS filter didnt add the right color to the top of the tree as it did to the bottom :P



Jun 03, 2013 at 11:58 PM
JimFox
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p.1 #7 · p.1 #7 · Astrophotography White Balance


Don't use a graduated filter in Photoshop. I never use them, though I know some do. Use a layer mask where you select what will see through to the layer below. Trees like you have in the shot above will take a bit more work, but that's the way I would do it. If you haven't used manual layer masks before, this would be a good time to practice...

So now, with your original shot, it would be super simple to just use a layer mask for the ground layer, or at least just the barn, and select it. Use a lasso, select around the barn, feather the selection slightly and click on the Layer Mask Icon in the Layer group box. Then on the layer below, use a plain old warming photo filter from the Edit menu, and adjust the opacity of it as needed. You could do it in 3 minutes...

Jim



Jun 04, 2013 at 12:04 AM
kodakeos
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p.1 #8 · p.1 #8 · Astrophotography White Balance


yeah the first image was somewhat easy. I do layers a lot for 2 shot HDRs and whatnot.

The second image was really tough, which is why I wanted to figure out my gel issues.



Jun 04, 2013 at 01:31 AM





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