Re: Polaroid Reciprocity

Guillermo,

Will the equation change with different types of film? Or do I just plug
the indicated time into the equation to get a starting point? If it does
change, which numbers will be different and how do I figure them out?

Thanks

Jason Russell
WISH-TV
Indianapolis, IN

"If you go any faster we're gonna travel back through time."
----- Original Message -----
From: "Guillermo" <penate@rogers.com>
To: <pinhole-discussion@pinhole.com>
Sent: Monday, October 28, 2002 6:43 PM
Subject: Re: [pinhole-discussion] Polaroid Reciprocity

>
> ----- Original Message -----
> From: "Jason Russell" <jrussell@wishtv.com>
>
> > I was wondering if anyone could help me with Polaroid Reciprocity. I
just
> > recently started shooting with a Santa Barbara (2 inch Super Wide) with
a
> > Polaroid back. Right now I'm shooting with Polapan 400 B&W (72). I've
> done
> > most of my shooting outside and the exposures have all been less than
six
> > seconds. I wanted to try shooting inside under much lower light. I'm
> just
> > not sure how much I need to compensate for reciprocity. I checked out
the
> > info on Polaroid's site, but I'm still a unclear.
> > Has anyone else shot with this film or a similar film that could give me
> an
> > idea of how much time to add.
> > The shot I want to shoot right now, by my calculations is about 2 and a
> half
> > minutes without compensating for reciprocity.
>
> Jason:
>
> I have not used the film, nevertheless here is my suggestion:
>
> Short answer: for indicated 2.5 minutes you should give 17 minutes 3 secs.
>
> Long answer: As you can see on the Reciprocity Performance chart, the
> effective film speed decreases (as expected) as the indicated exposure
time
> increases, the exposure adjustment column tells you how many stops you
> should increase the indicated time. For 4 secs, for instance, the
exposure
> adustment is 1 stop, that means you should double the time to 8secs. I
made
> some math calculations (best curve fit) and they predict that when the
> indicated exposure time is 150secs (2.5minutes), the effective film speed
> will be ISO-58.6, which in turn will need an exposure adjustment of 2.77
> stops, for a total of 1023secs or 17 minutes 4 secs (150 x 2^2.77 = 1023).
> If you want some other times, use the following formula:
>
> T = corrected time
> I = indicated time
> * = multiplication sign
>
> T = ( 0.021 * I * I ) + ( 3.708 * I ) - 4.89
>
> CAVEAT: the above suggestion is just an educated starting point based on
the
> Polaroid published information, YMMV.
>
> Guillermo
>
>
>
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Received on Tue Oct 29 09:36:25 2002