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Re: [APML] Agfa Optima Prestige film
Hi Walter:
+ 2 stops means that you need four times as much exposure (for equal
density) as predicted from bright conditions. So if the exposure is
predicted to be 10 sec at f/8, you will actually need 10 sec at f/2.8, or 40
sec at f/8.
My advice regarding your Arizona trip is to take a half-dozen rolls of E200
or Provia F400. These films have proven themselves for astro imaging. The
E200 is a bit stronger on reds (some say too strong, but I like it).
Bert
Bert Katzung
katzung1@comcast.net
www.astronomy-images.com
----- Original Message -----
From: "Walter Willis" <wwillis1@qwest.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Monday, 25 August, 2003 6:11 PM
Subject: Re: [APML] Agfa Optima Prestige film
> Pardon my lack of knowledge - what does it mean by +2 f-stops. Does it
> mean that on a lens with f/1.7, f/2, and f/2.4 that instead of f/1.7 I
> need f/2.4? Or is it the other way around?
>
> Walter
>
> Bert Katzung wrote:
>
> > Hi Walter:
> > 2 stops at 100 sec signifies serious reciprocity failure. If it was
> > equal across the 3 layers, it wouldn't be so bad, you could compensate
> > by increasing exposure more. Unfortunately, it is rarely equal and as
> > a result, as in the examples on my webpage, the color balance gets
> > horribly skewed.
> > Bert
> >
> > Bert Katzung
> > katzung1@comcast.net <mailto:katzung1@comcast.net>
> > www.astronomy-images.com <http://www.astronomy-images.com>
> >
> > ----- Original Message -----
> > From: Walter Willis <mailto:wwillis1@qwest.net>
> > To: Discussion of Film Astrophotography
<mailto:astro-photo@seds.org>
> > Sent: Monday, 25 August, 2003 3:10 PM
> > Subject: Re: [APML] Agfa Optima Prestige film
> >
> > The AGFA data sheet actually does show some reciprocity info, up
> > to 100 seconds exposure. With this film it calls for an
> > adjustment of +2 f-stops.
> >
> > Walter Willis
> > Life without chocolate is too terrible to contemplate
> >
> >
> >
> > ----- Original Message -----
> > From: Roland Roberts <mailto:roland@astrofoto.org>
> > To: astro-photo@seds.org <mailto:astro-photo@seds.org>
> > Sent: Monday, August 25, 2003 2:57 PM
> > Subject: Re: [APML] Agfa Optima Prestige film
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> >
> > >>>>> "Bert" == Bert Katzung <katzung1@comcast.net
> > <mailto:katzung1@comcast.net>> writes:
> >
> > Bert> I've never used Optima Prestige, but recommendations
of
> > Bert> daylight photographers, professional or otherwise, are
> > Bert> generally worthless for astro applications. The
> > reciprocity
> > Bert> characteristics of films are generally unknown to
> > them (and
> > Bert> sometimes to the manufacturer as well, when it comes
> > to 1
> > Bert> hour exposures) and reciprocity is critical for our
> > stuff.
> >
> > As a small footnote to this, I recently picked up a book on
large
> > format photography. Interestingly enough, it has a set of
charts
> > showing reciprocity adjustments for a large number of films.
The
> > chart only extends to about 120 seconds (nominal, the adjusted
> > exposure may be much longer). So *some* professional
> > photographers
> > are at least aware of the problem. Too bad Kodak, Fuji, Agfa,
> > etc. don't publish similar charts....
> >
> > regards,
> >
> > roland
> > - --
> > PGP Key ID: 66 BC 3B CD
> > Roland B. Roberts, PhD RL
Enterprises
> > roland@rlenter.com
> > <mailto:roland@rlenter.com> 6818
> > Madeline Court
> > roland@astrofoto.org
> > <mailto:roland@astrofoto.org>
> > Brooklyn, NY 11220
> >
> > -----BEGIN PGP SIGNATURE-----
> > Version: 2.6.3ia
> > Charset: noconv
> > Comment: Processed by Mailcrypt 3.5.4, an Emacs/PGP interface
> >
> > iQCVAwUBP0qGPOoW38lmvDvNAQHgCwQAsYeGMqu7mF6cXXB5mphrY0qI+0YmKxr2
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> > B+njI8WOrt0=
> > =NRTP
> > -----END PGP SIGNATURE-----
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