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

["westergren" <westergren@netzero.net>]

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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