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 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.glori...@sympatico.ca> > > To: Pinhole List <pinhole-discussion@p at ???????> > > 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 > > > > _______________________________________________ > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.???????/discussion/
