Re: [APML] NGC7822, Ced214, and Sh2-170

["tan@home.com" <tan@home.com>]

Chuck,

	I see what you mean about the color of the sky fog effecting the 
exposures. This never occured to me <g>. I agree that the exposure 
ratios should be set according to your technique of the graduated 
grayscale for correct color balance. However, given that the exposure 
ratios have been determined in this manner, my thoughts were that if I 
exposed to the sky fog limit for each filter then I would obtain the 
best signal to noise ratio for each channel at the expense of making 
color accuracy secondary. Later on during Photoshop processing, color 
can be somewhat post-compensated. This way I get the best overall SNR 
with reasonably accurate color.
	Alternately, if I had stuck to the correct color ratios all the time, 
there will be two channels which will be exposed past sky fog limit and 
might be too dense. I am assuming all 3 RGB channel have a different sky 
fog level after normalizing with the correct exposure ratios. 
Alternately, I can expose so that only one of the channels is at the sky 
fog limit, then I would sacrifice SNR for the other two channels. At any 
rate, these were my thoughts concerning the different exposure ratios I 
had used in the past.

Loke



Chuck Vaughn wrote:

> Loke,
> 
> The correct exposure ratios are not necessarily where the sky fog is the
> same on all three. The color of the sky fog influences that.
> 
> The correct exposure ratios are those that create the same densities
> of a grayscale step chart through each filter. With my filter set that
> means the blue and green require twice the exposure as the red.
> 
<snip>



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