> William,
Since photograpic paper is designed for the longer exposures common for enlargers, its reciprocity departure is not as severe as that for photographic film, but it is present and does need to be factored into the exposure. Most black and white papers seem to have a "speed" equivalent to about ISO 6. Starting with some figures in Jim Shull's book "The Hole Thing" and adding some other data points and my own experience, I have come up with the following set of values: Indicated Reciprocity Exp. Time Corrected 15 secs 30 secs 45 secs 2 mins 1 min 2 min 45 secs 2 min 6 min 3 min 11 min 4 min 15 min 30 secs 5 min 20 mins 10 min 50 mins 20 min 2 hours 40 min 5 hrs 20 mins (These numbers line up on my screen, but e-mail may jostle them significantly.) Check George L. Smyth's site -- the article by Penate. Also look at the 'airtime' site in the UK. (Don't have the URL right now, just a note penciled onto my graph.) My current f/360 pinhole needs 4 minutes with Ilford MGIV on a sunny day. If you start at 1/6 second at f/16 and work your way up to f/360, you will arrive at an indicated time of about 76 seconds. Reciprocity then takes it up to nearly 4 minutes. Adding a yellow filter pushes the time up to 10 to 11 minutes. As usual, your mileage may vary, but half the fun of pinholing is in the experimentation. Bob San Jose, CA > --__--__-- > > Message: 1 > From: "William Erickson" <erick...@ic.mankato.mn.us> > To: "pinhole Discussion" <pinhole-discussion@p at ???????> > Date: Mon, 4 Dec 2000 13:47:33 -0600 > Subject: [pinhole-discussion] reciprocity failure with paper negaties. > Reply-To: pinhole-discussion@p at ??????? > > I've been doing some multiple hour exposures on kodak polymax paper and I > got to wondering at what length of exposure with a paper negative do you > need to begin to factor in reciprocity failure. My results suggest that the > answer may be around 1 hour. Any ideas?
