From: George Anderson 
To: Dominic-Luc Webb 
CC: atm{at}shore.net
Reply-To: George Anderson 


Hi  Dominic

From what I can remember of my photography classes in the 70's most
photographic papers have an equivalent film speed in the 3 to 10 ASA range.
Most astrophotography is done with films between 200 and 800 ISO/ASA.
From my front yard with 200 ASA film I start reaching saturation at around
ten minutes at f/2.
If I were to use paper with a speed of 6 in the same instance my exposure
time would jump to 320 minutes, and that does not allow for any reciprocity
failure of the paper. It isn't uncommon for many films to lose 2 F stops in
a five minute exposure, and the failure rate is not the same for the
different layers.
Also any additional time would increase the risk of something going wrong
during the exposure.

George Anderson
Montreal Canada

Clear skies and good health

Dominic-Luc Webb wrote:
>
> Lately I have been eyeballing the print paper that my images from
> photographic film would end up on. Since the final product of my
> photography ends up on this paper anyway, is there some reason why
> we do not use this directly? For that matter, why not X-ray film?
>
> I was told that the standard paper is not very sensitive, which is
> reason not to use it. On the other hand, one local pro photo shop
> manually prints my fainter photographic film images onto a less
> common sensitive high contrast paper that the automatic machines
> cannot process. Anyone have any thoughts on pros/cons of using
> these papers directly on the scope?
>
> Dominic

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