Re: Reciprocity failure with paper

Guy,

Back in the 1974 Jim Shull published "The Hole Thing", a pinhole photography book which includes a table of
reciprocity corrections for enlarging paper used in pinhole cameras. (Apparently he was using Luminos
Industrial F which he rated at an ASA of 10.)

Using Shull as a starting point and gathering a few other data points from web sites such as those of George
Smyth, Airtime, and Penate and adding in my own experience, I have constructed a reciprocity table that works
for orthochromatic B&W paper in pinhole cameras in sunlight:

Indicated Exposure Corrected exposure
32 secs 1 min 15 secs
45 secs 1 min 50 secs
64 secs 3 mins
91 secs 4 mins 40 secs
128 secs 7 mins
181 secs 10 mins 50 secs
256 secs 16 mins 40 secs
362 secs 25 mins
512 secs 40 mins
724 secs 64 mins
1024 secs 104 mins

Using this table, I can consistently get good shadow detail (an indication of proper exposure) with Agfa
Multicontrast Premium and Ilford Multigrade IV RC papers. Although these papers have different published
paper speeds, I have found that assigning them the same "daylight ASA" of 6 works in practice.

In the darkroom under enlarger light, B&W paper does not seem to exhibit much reciprocity departure up to
times around two minutes. Possibly the fact that in sunshine the light meter is measuring a good deal of
light to which the paper is not sensitive may account for some of the variation from indicated time. My
pinhole cameras have had f/stops ranging from about 180 to about 360, so most of my work has been in the 4 to
40 minutes range.

Bob

p.s. I have also found that using a yellow filter on the camera with these papers lowers the contrast and
yields a paper negative that is much easier to print, but of course still results in that "orthochromatic
look". The filter blocks UV and allows you to optimize the camera for the wave lengths to which the paper
responds, i.e., about 500nm.

>
> Message: 15
> Date: Sun, 16 Dec 2001 02:43:05 -0500
> From: Guy Glorieux <guy.glorieux@sympatico.ca>
> To: Pinhole List <pinhole-discussion@pinhole.com>
> Subject: [pinhole-discussion] Reciprocity failure with paper
> Reply-To: pinhole-discussion@pinhole.com
>
> Hi everyone,
>
> Does anyone have information about reciprocity failure with paper. I
> have to print large format prints which require long exposures (several
> minutes) and can't open the lens without creating vignetting on teh
> edges of the print.
>
> It would help if I could know more about the appropriate correction
> factor to use for exposure times of say 1 minute, then 2 minutes, then
> 3minutes and so on.
>
> Thanks,
>
> Guy
>
Received on Sun Dec 16 14:24:58 2001