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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
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> roland@astrofoto.org
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>
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