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kintatsu
01-06-2013, 07:40 AM
Just a quick question for someone at the source. HP5+ and FP4+ both have an identical reciprocity chart. Numbers on the net are all over the place.

What is the correct data, and is it available in some kind of table format?

hoshisato
01-06-2013, 08:59 AM
I think most people use this article by Howard Bond as the best resource for reciprocity information for HP5+ and other films: http://www.willwilson.com/articles/0403Bond_Reciprocity2.pdf
It is an interesting read and shows that the Ilford provided information doesn't seem to sync with what what needs adding.

andrew.roos
01-06-2013, 10:01 AM
I agree that Howard Bond's data is a good resource. I recently measured reciprocity failure for Delta 100 (see post here (http://www.apug.org/forums/forum37/113545-measured-reciprocity-failure-ilford-delta-100-a.html)) and my measurements differed substantially from the chart in the Ilford data sheet.

Andrew

DWThomas
01-06-2013, 10:24 AM
I agree that Howard Bond's data is a good resource. I recently measured reciprocity failure for Delta 100 (see post here (http://www.apug.org/forums/forum37/113545-measured-reciprocity-failure-ilford-delta-100-a.html)) and my measurements differed substantially from the chart in the Ilford data sheet.

Andrew

One of these days I should sort it all out, I suppose. I used Delta 100 in one of my early Pinhole Day forays and used a chart put out by Pinhole Designer that included compensation for reciprocity failure. The results suggested to me that the exposures had been excessively compensated, so maybe the P.D. software designer used the Ilford data. (More recently I've used Acros and ignored the whole thing.) Probably within the exposure range most "ordinary" people use, there's not enough of a problem to justify grinding through the tests.

kintatsu
01-07-2013, 02:46 AM
Thanks for the quick replies and the link. I downloaded an Ipad app and it gives differing results than others, also. I'll try the Bond times after trying the app times. I've noticed that with my flash in use, it's less of a problem, but would like to be able to use only natural light and longer times.

Thanks again, everyone!