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Re: [APML] Portra 800? was: 4x5 color negative
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
Bert Katzung
katzung1@attbi.com
www.astronomy-images.com
----- Original Message -----
From: "Jerry Lodriguss" <jerry@astropix.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Tuesday, April 22, 2003 8:54 PM
Subject: RE: [APML] 4x5 color negative
>
> >No problem. I will have to use E100 and push it. Another thought I had
was
> >to use Portra 400. I know it's peak response in not in the red but it's
> >speed is ISO400. So it would seem to be much faster than E100. Maybe I
could
> >rebalance the color in Photoshop when I am done. Any opinions anyone?
>
>
> The Portra 160 and 400 might work ok for the blue and green channels, but
I
> don't think it will work very well for the red channel because the red
> response is way down at 650. The Portra 800 on the other hand looks like
> it peaks in the red response at 650, although the red is still less than
> the green and blue.
>
> You know, judging by the great results I've seen from people like Stephen
> Pitt ( http://www.light-to-dark.com/Rho.html ) and John Boudreau (
> http://home.attbi.com/~jeboud/m42.htm ), I think the Fujichrome Provia
100F
> might be your best bet in 4 x 5.
>
> Jerry
>
> Jerry
>
> The book "Photoshop for Astrophotographers" is now finished!
>
> Go to: http://www.astropix.com/PFA/PFA.HTM
>
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