Re: [APML] NGC 6914 Tech Pan Tri-color and CCD comparison

[Aplanatic@aol.com]

Thaomas wrote:

> you have to take into account, that both images have been taken at
>  different f/ratios. Just to correct the exposure ratios:
>  
>  CCD: 3*6 + 3*6 + 3*10 = 66 min at f/5.4
>  
>  TP: 3*180 = 540 min at f/8
>  
>  Hence the real factor between both is 540/66 * (5.4/8)**2 = 3.73, which
>  is considerably less than 10, but impressive anyway.

Strictly speaking, the S/N of an image is dependent only on the aperture of 
the instrument and exposure time and not the f/ratio, as long as the images 
are compared at the same image scale.  Because of LIRF, this is not 
necessarily true for film.

Dave Rowe


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