pinhole-discussion:: Re: Polaroid Reciprocity

From: Michael Healy <mjhealy_at_domain.name.suppressed>
Date: Thu 31 Oct 2002 - 06:48:00 PST

Is this code for something? Does everybody else in alternative processes already know what this means? Am I just out of loops?

Mike Healy
  ----- Original Message -----
  From: ROBERTSON,TRAVIS J
  To: 'pinhole-discussion@pinhole.com'
  Sent: Wednesday, October 30, 2002 12:55 PM
  Subject: RE: [pinhole-discussion] Polaroid Reciprocity

whatever geek

  -----Original Message-----
  From: Guillermo [mailto:penate@rogers.com]
  Sent: Tuesday, October 29, 2002 8:28 PM
  To: pinhole-discussion@pinhole.com
  Subject: Re: [pinhole-discussion] Polaroid Reciprocity

  ----- Original Message -----
  From: "Jason Russell" <jrussell@wishtv.com>
>
> The corrected time you gave me worked very well. Thank you!
>
> However, I want to clarify one thing...
>
> Did you go to the Polaroid website to get the numbers to plug into the
> WinCurveFit program? Did you just pull the numbers from the displayed
  graph
> and plug them into the program and extend the curve? Is that how that
> works.

  Jason, altho I could have used the graph to get some "indicated versus
  corrected" values, that graph is just too coarse and since some values are
  already given in the "Reciprocity Performance" table, that's what I used.
  Now, that table (or graph) gives you corrected values in terms of extra
  stops of Exposure Adjustment, so we need to translate the indicated
  exposures to corrected exposures in seconds. For full stops it is easy, you
  double the indicated exposure for each stop of adjustment, but what about,
  for instance, the corrected exposure for an indicated 16 secs and an
  adjustment of +1 2/3 stops? To do it, you have to use the following
  equation:

  I = indicated time
  T = corrected time
  n = exposure correction in stops
  ^ = raised to the power of (need scientific calculator to do it, I use
  CALC98, freeware program downloadble here
  http://www.calculator.org/download.html)

T = I * (2 ^ n)

In the case of 16 secs and 1 2/3 stops adjustment, it would be:

  T = 16 * (2 ^ 1 2/3)
  T = 16 * (2 ^ 1.6666)
  T = 16 * 3.17465
  T = 50.79 secs

Once you have all the corrected values in seconds, feed the indicated and
corrected values to the WinCurveFit program.

  I have to mention that I don't bring a calculator with me when I go out to
  make exposures, I prefer to make a graph, very much like this one
  http://www.kodak.com/global/en/professional/support/techPubs/f9/f002_0062gc.
  gif and use that to find corrected times.

Guillermo

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