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Re: [APML] Film Questions
Hi Clay:
I'm certainly not in the film guru class of Don Westergren or Pat Freeman
and the others, but I know that the big problem with Portra films and Supra
800 (for example) is the reciprocity failure of the cyan layer. This layer
fails much sooner than the other layers so you end up with a positive image
that looks extremely color distorted, eg, cyan. See my brief tests of Supra
800 at:
http://www.astronomy-images.com/Tests/test-of-kodak-Supra800-film.htm
And of course, reciprocity failure in any or all layers is something that
cannot be predicted from the spec sheets that the companies put out on their
web sites. You have to test it yourself or rely on tests by other astro
imagers going out to 30-60-90 minutes rather than the 10 second maximum that
the companies use.
Bert
Bert Katzung
katzung1@attbi.com
www.astronomy-images.com
----- Original Message -----
From: <ckessler@gatecom.com>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Thursday, April 17, 2003 4:54 AM
Subject: [APML] Film Questions
> Hi List,
>
> I have been thinking about this film situation that we find ourselves in
> (always dangerous) and I think I need some help understanding why the
current
> films don’t work well. I was looking at the spectral curves on the
Kodak
> web site for the recent successful films and the sensitivity for 653 nm
seems
> to be as follows:
>
> PJM 640 2.0 log in cyan
> PJ 400 2.5 log in cyan
> LE 400 2.5 log in cyan
> SUPRA 400 2.4 log in cyan
> PPF 400 2.5 log in cyan
>
> The newer available films are thus:
>
> Portra 400 2.0 log in cyan
> RG 400 Hi Def 2.0 log in cyan
>
> Now, it seems to me that while 653 nm is not the peak in the cyan forming
> region for either of these new films it does have the same sensitivity as
the
> old “Multispeed 640” and I remember that as a wonderful
astrophoto
> film. As a comparison E 200 slide film has a 1.6 log sensitivity in this
same
> 653 nm wavelength and this is considered a great transparency film for
> astrophotos.
>
> I guess my question would be:
> “Why does 2.0 log in PJM and 1.6 log in E 200 work for
astrophotography
> and 2.0 log in Portra 400 and RG 400 High Def. not work?”
>
> I must be missing something here. I do notice that the newer films have a
> slightly higher sensitivity to OIII and H-beta than the discontinued ones.
> Does this mean the new films would be better than the old ones for
shooting the
> horsehead? Perhaps one of the more knowledgeable “film
> Guru’s” can straighten out my thinking here.
>
> Thanks
>
> Clay Kessler
>
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