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Re: [APML] Agfa Optima Prestige film

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
www.astronomy-images.com
----- Original Message -----
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 -----
Sent: Monday, August 25, 2003 2:57 PM
Subject: Re: [APML] Agfa Optima Prestige film

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>>>>> "Bert" == Bert Katzung <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                            6818 Madeline Court
roland@astrofoto.org                           Brooklyn, NY 11220

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