From: Christina Z. Anderson (zphoto@montana.net)
Date: 04/13/02-08:47:29 AM Z
Shannon,
I checked this chart out that Gord mentions, below, and mine is
infinitely more usable and understandable (how's that for being humble! But
seriously...). However, it is an attachment and I would have to mail it to
you offlist. It is an excel spreadsheet or a works spreadsheet so you'd
have to have one or the other on your computer, but with one plug in of your
pinhole fstop number all the times change for that particular pinhole. I
also have every film speed on the left side of the chart so you basically
choose your film speed line and run with it. I made the whole chart based
on the following formula:
(time @ f16)(pinhole f-stop squared)
______________________(this is a "divided by" line)
16 squared
This is based on the inverse square law of light. I had to enter each cell
with the calcs (which you, of course, don't see or have to worry about) and
it was a b--ch so please acknowledge my authorship if you pass it along!
(Christina Z. Anderson)
How you use the chart, after you plug in the number, is that you take
your hand held light meter, plug in your ISO and a shutter speed that
matches that ISO (eg: 100 ISO of film and a shutter speed of 1/100 or
actually 1/125) and get an fstop read. Then you follow that fstop column
down to where the fstop column and the film ISO row intersect, and there's
your time. Then you consult reciprocity failure on the left of the chart.
This is based on the sunny 16 rule. If the weather is not giving you a
sunny 16 but an fstop of even, let's say, f1 that you should be using, then
you just consult the f1 column and run down it until you intersect with your
ISO and there you have it. I have about 20 different pinhole fstops and
that many charts, with the change of one cell on the sheet.
However, if you are using Neopan Acros, there is no reciprocity failure
until 128 seconds, and i mean NO. Then at 128 seconds you add 1/2 stop up
until, I think it is 1000 seconds. So you do have to really watch your
film's reciprocity failure. Maco IR film, for instance, is dismal in this
department.
I did a test; I took 12 different pinhole sizes on and off the front of
my 35mm camera body cap. I tested each pinhole with my chart, using my
calcs exactly, and exposed accordingly with Neopan Acros. Every single
exposure I printed an 8x10 of at the exact same printing time. It proved to
me that Acros was correct in saying there was no reciprocity failure. In
fact, even when I added the 1/2 stop, it overexposed it just a tad.
What is nice about this chart is that you can bring it with you in the
field and when changing film from 3200 down to 1 ISO you've got all the
times. The only thing is that the times are all in seconds, so when you get
an f1 read on ISO 1 film you'll have some astronomical second count in the
10,000's so you'll just have to divide by 60 to get your minute count. I
don't suppose you'll often be shooting this speed of film in the dark, tho
:)
Chris
> Hi:
>
> I use Larry Fratkin's pinhole calculator at
>
> http://www.MrPinhole.com/Exposure.html
>
> This web page does the math for you. You enter the f-stop of your camera,
> it then creates a table that lists "normal" camera exposure times and
> their equivilant exposures using your f-stop.
>
> To use the table you take a meter reading and find this on the table. In
> the far left column on the same row as your meter reading you will find
> the exposure for your f-stop.
>
> Hard to explain, but it works. I calculate the f-stop for each camera. I
> feed this into the form print out the results and tape it to each camera.
>
> With this I can convert standard light meter readings on the spot without
> doing any math :)
>
> Gord
>
> ---------------------------------------------------------
> Gordon J. Holtslander Dept. of Biology
> holtsg@duke.usask.ca 112 Science Place
> http://duke.usask.ca/~holtsg University of Saskatchewan
> Tel (306) 966-4433 Saskatoon, Saskatchewan
> Fax (306) 966-4461 Canada S7N 5E2
> ---------------------------------------------------------
>
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