Bergger BPF Reciprocity

[Matthew Hoag]

Does anyone have experience with the reciprocity characteristics of Bergger BPF2 00? They supply a chart up to 30 seconds metered exposure but I frequently expo se well beyond 30 seconds. How hould I extrapolate beyond that? BTW my EI is 6 4 if that makes any difference.

Thanks for any help provided!

Matthew

[Doremus Scudder]

Matthew,

I've been shooting BPF back-to-back with Tri-X for some time now (although at EI 160!) and have been using a table based on the Kodak reciprocity table for conventional black-and-white films. I've extended Kodak's table to include exposures up to 300 minutes, but it is the same curve for all intents and purposes. I've had excellent results from the BPF this way with exposures up to 20-25 minutes. The BPF seems to hold a bit more shadow detail than the Tri-X as well.

You can find the Kodak data at their web site in a technical document entitled "Reciprocity and Special Filter Data for KODAK Films" (sorry, I don't have the URL). You should get good results using the times and development recommendations there.

If you regularly do a lot of ultra-long exposures, you might want to take a look at the thread from a week or so ago on the topic of development adjustments for reciprocity failure. My post there includes my development adjustments and times for Kodak films up to 300 minutes.

Hope this helps a bit,

Regards, ;^D)

[Matt_1193]

First off - I'd take a hard look at your E.I. - how did you arrive at such an adjustment? 40% of rated speed seems awfully slow.

[Matt_1193]

....Excuse me - it's more like 27%!

[Matthew Hoag]

Regarding my EI: I am still evaluating my tests and shooting based on just getting started with BPF, PMK Pyro, Azo & Amidol. I'd rather too much density than not enough, and I may revise my EI as I progress.

Matthew

[Ed Buffaloe]

If you go go my Articles (http://unblinkingeye.com/Articles/articles.html) page and click on the article entitled "Exposure Calculator for Pinhole Exposures," you will find a printable calculator that can calculate very long exposures. The times are for Tri-X and T-Max 100, but can be extrapolated to other films. There is also room to add data for one other film. In your case, I would use the times for Tri- X.