Guillermo, I also have been through a lot of calculations like this, however, for reciprocity corrections for photo paper emulsions I resort to a table that I have gleaned from several sources and tweaked from experience over the years. (As I am sure most of you know, reciprocity departure for paper emulsions is much less severe than for film emulsions.)
The one possible flaw in your analysis below is that the K8 filter has a correction factor of 2, or 1 f/stop, for panchromatic film. For photo paper it will be something else, probably close to that for orthochromatic film, or about 1 1/3 f/stops. (I have yet to try Panalure paper. It is on my to-do list; Volume XXIV, Chapter 17, page 183. That's pretty near the top.) In any event, I usually assume the "speed" of the paper emulsion is about 6, and then depending on the subject matter, my patience on that day, and my fear of under exposure, I make darn sure I am getting enough light. If I were to reverse engineer my exposures, I would probably find that in most cases I am treating the paper as if its "speed" is around 4. I toyed with several different developing methods before resorting to the yellow filter. In paper developer, most RC papers with their incorporated developers develop far too quickly for development by inspection. Film developers are a little softer and, if diluted, can give you time to pull out the negative if necessary. I even tried developing incorporated-developer papers in a lye solution, but I hated working with that stuff. The f/360 camera to which I referred is a 120 degree panchromatic camera with a 4 x 11 inch negative on a 5 inch radius of curvature. It is great fun, especially as on-lookers gather around during the 10, or so, minute exposures. Bob p.s. Thanks for all your informative help and suggestions over the years. You are a model citizen in this community. ======================= > > ----- Original Message ----- > From: "HypoBob" <hypo...@pacbell.net> > > > > As for exposure time, my f/360 camera with Ilford MGIV and a yellow filter > needs about 8 to 10 minutes in full sun. On sunless days I do not use a > filter, but the lower light levels still demand about the same exposure > time, if not more. > > MGIV behaves as ISO-3 for you, then. > > According to "sunny16" rule, under sunny skies your exposure should be f/16 > @ 1/3 seconds. There are 9 full stops between f/16 and f/360, therefore > f/16 @ 1/3 seconds becomes f/360 @ 170 seconds. A K8 filter has a factor of > 2, that makes the exposure f/360 @ 340 seconds, reciprocity correction > factor would be around 1.5 (as per reciprocity correction table in my small > article http://members.rogers.com/penate/pinsize.htm ), that makes the > exposure f/360 @ 510 seconds or f/360 @ 8 minutes 30 seconds. > > Guillermo > > --__--__-- >
