Thanks Bob,
This is the most comprehensive piece I remember having seen on the list. I
guess I should have gone back to the
archives and checked earlier postings since the topic has been covered many
times before. But then I would have
had access to this piece.
Well worth flagging for the next time someone raises the question.
Cheers,
Guy
HypoBob wrote:
> 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 secs10 mins 50 secs
> 256 secs16 mins 40 secs
> 362 secs25 mins
> 512 secs40 mins
> 724 secs64 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
> > To: Pinhole List
> > Subject: [pinhole-discussion] Reciprocity failure with paper
> > Reply-To: pinhole-discussion@p at ???
> >
> > 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
> >
>
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