>
> Michael:
>
> The meaning of what you are saying has finally dawned on my muddled brain.
>
> Based on what you have said, and your tests, I conclude that the retroprocity
> failure of film emulsions as opposed to the linear response of CCD chips
> prevents a direct comparison between film and CCD chip speed. Maybe this
> would be possible with gas hypered film, I don't know.

I gas hyper 2415 and color film. At shorter exposures, I shoot my gas
hypered film much like non gas hypered film. Covington and Marling
predict speed gains while Ware, myself, and others are skeptical. Part
of the reason may be Covington and Marling are more experienced with
older film emulsions (2415) whose ISO speed certain exposures might
have been effected. In addition, Covington's methodology for testing film
uses a light source that is too bright thus likely skewing his results.
Newer Kodak film emulsions (PPF, PJM) seem to respond much less to
hypering in speed and sensitivity increases but tend to shift the colors
away from red towards blue.


> For my film astrophotography I have been using an exposure calculator based on
> the "fx System" presented in Barry Gordon's excellent book. I would like to
> extend this method to the CCD, but it dosn't appear possible.

Actually, it might work. Gordon's Fx System works great for short film exposures
but neglects reciprocity failure. His system is based on the ISO ratings of film
which fall apart in a few minutes. But for CCD with no reciprocity failure, his
system just might work.


> Given that a given CCD chip has a certain quantum effeciency, is it possible to
> calculate the exposure value by knowing the f/stop and magnitude per square
> arc-second of a deep space object? Are there any books on the subject
> (The Cookbook?).

Yes, Richard Berry uses a system of B values assigned to objects that is
used in an exposure equation to get within a factor of two. I believe details
are in his book Choosing and Using a CCD Camera. These values could
be used for Pictor CCD cameras as well.


> Any help you can give me will be greatly appreciated.
>
> Chris Frye
> Silver Spring, MD



--
Michael Hart
Husen Observatory

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