[ATMoB-discuss] First photo from C14/ST7

[John Boudreau]

Hi Paul,

In daylight photography, there isn't really a noticeable color balance problem from clear skies to hazy skies where there is a big color temp difference ranging from 5,000 to 20,000° K. Only when the Sun is quite low in the sky where absorption comes into play is there a real color balance problem between the RGB channels.

I think this holds true for the night sky. Some imagers take the time to correct color balance by checking their imaging setup vs. solar analog stars (G2V). But they don't take the time to do this for every transparency variation... but the results are quite similar from night to night. Chuck Vaughn, who is probably taking the best DSLR astro images around, balances color by calibrating in daylight with a MacBeth Color Checker Chart. His results are pretty close to many G2V calibrated night sky images. Only color balance corrections due to varying atmospheric absorption/altitude appear to be really necessary, and IMO they are only really noticeable for up to 60° altitude. 

Other problems like night sky color variation take place, but I don't think they are really as big a deal as some imagers make them out to be. Too many of them take their 'carefully calibrated' imaging result and end up tweaking the final color balance and saturation to taste anyway ;o)


---John


----- Original Message ----- 
From: <valleli at rcn.com>
To: "John Boudreau" <jeboud at comcast.net>; <atmob-discuss at atmob.org>
Sent: Wednesday, August 09, 2006 3:43 PM
Subject: Re: [ATMoB-discuss] First photo from C14/ST7


> John,
> Is there any problem in color photography from the fact that the color temperature of the sky is about 8000 deg.K at the zenith?
> I imagine it drops to about 3000K near the horizon at sunrise/set.
> 
> Paul
>