I use the formula, y=.91x^1.51, where x is the metered time and y is the corrected time. It approximates the reciprocity pretty closely, and has worked for me for exposures up to 2 hours on FP4+, which shares the same reciprocity failure as HP5+. I've always processed normally, with pmk pyro.
John ----- Original Message ----- From: bwphoto4...@aol.com To: pinhole-discussion@p at ??????? Sent: Friday, July 19, 2002 8:26 PM Subject: [pinhole-discussion] HP5, Delta films and reciprocity OK, This has probably been discussed recently, but can anyone out there recommend a good formula/rule of thumb for adjusting exposure for reciprocity in Ilford films? The technical data on their webpage is merely a chart, and I am hoping to get more specific information, based on the experience of the other pinhole photographers on the list. I normally use Delta 400, but occasionally use HP5 and Delta 100. I process in Ilfotec DDX (although I also occasionally use Ilfosol). Anyone out there with experience with these films? My camera is the Zero Image multiformat (which is at f235). Thanks! M Billingslea
