Re: 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
Received on Mon Oct 28 18:44:01 2002