Re: [APML] Push Processing (was Scanning slides)

[Jerry Lodriguss <jerryapml@astropix.com>]

>  To get a good
>astro picture with slide film, you have to expose long enough to get an
>image of the deep sky object without a  light sky background.  For slide
>film in particular, you also have to avoid "sky fog" where the background
>sky shows up as gray rather than black in the picture.  You should expose
>slide film at various times to find where the sky fog limit is for your
>film, equipment and sky darkness, then always expose shorter to avoid sky
>fog.  Slide film exposed this way will scan easier.  Slide film that is
>underexposed is difficult to scan, as you are finding out.


Hi Don,

With slide film, I don't think you should avoid sky fog at all. You WANT 
the sky background to be somewhat gray (if you're lucky enough to be in a 
really dark location) and not black.  I don't think you should find the sky 
fog limit and then expose shorter. I think you should expose to the sky fog 
limit, or longer with slide film if the object does not have extremely 
bright parts like M42.

You do NOT want the sky background to be black. if it's black, it's 
underexposed.

The further up on the characteristic curve you can put the shadow detail, 
the better off you will be because it will have more contrast, and because 
it will be easier to scan.

Jerry




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