Re: [APML] Portra 800? was: 4x5 color negative

["Bert Katzung" <katzung1@attbi.com>]

Hi Don:
Yes, I knew that there were several negative results with Portra 800 that
were posted and I was surprised to see it mentioned as a possibility again.
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "westergren" <westergren@netzero.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Wednesday, April 23, 2003 10:26 AM
Subject: Re: [APML] Portra 800? was: 4x5 color negative


> Bert,
>
> Pat Freeman and I both tested Supra800 with the same conclusion: it has
> extremely low red sensitivity.  I also tested Portra800, and the result is
> the same as Supra800.  My guess is that they are both the same emulsion. I
> don't use either for AP.
>
> Don
>
>
> >
> > Hi Jerry and all:
> > I've been haranguing about Portra 800 and Supra 800 for some time now
> > because they are awful for astro work. Not because of spectral
sensitivity
> > curves but because those curves are strictly for daylight exposure
times.
> > The cyan layer shows reciprocity failure much sooner than the other
layers
> > and being a negative film, we end up with a very cyan positive. See
> > http://www.astronomy-images.com/Tests/test-of-kodak-Supra800-film.htm
> > for the Supra result. I can't remember whether it was Pat Freeman or Don
> > Westergren who tested Portra 800 but  the result was the same. I think
> it's
> > time to put Supra 800 and Portra 800 behind us.
> > The bottom line is (as usual): the spectral sensitivity curve data have
to
> > be tested out at long exposure times. As given by the manufacturer,
those
> > curves are only the first step.
> > By-the-way: the book is great!
> > Bert
>
>
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>


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