# FP 4 reciprocity.

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• 09-25-2003, 09:04 PM
Jorge
Does anybody have a reliable reciprocity table for FP4, I will be shooting a really dark place on monday and would like to have good numbers.....pretty please...:P
• 09-25-2003, 09:11 PM
lee
I have one and it is at the darkroom and I will get it for you and post it for your tomorrow.

lee\c
• 09-25-2003, 10:41 PM
Jorge
Thanks Lee....aint APUG wonderful?!?...
• 09-26-2003, 01:11 AM
Lex Jenkins
I have no reciprocity data for FP4+, only anecdotal observations.

This has quickly become one of my favorites for nighttime photography. I prefer it in Diafine for that usage.

The maker of Diafine suggests an EI of 250 for use with FP4+. Instead, for nighttime use I halve that and rely on my F3HP's AE mode to establish a baseline exposure. I also estimate exposure based on the EV for a given scene (metered when possible, estimated otherwise). From there I'll bracket in full stops one up and one down.

So far this has given me at least one and usually more than one usable exposure. I simply treat the lighter or darker exposures as different interpretations of the scene.

For 35mm or rollfilm use I believe this is a viable method if you have enough time. If you're using sheet film or time is short and you can't bracket, by all means you'd want the reciprocity data.
• 09-26-2003, 01:14 AM
Jorge
Thanks Lex, but I plan to do it in 12x20, so bracketing is out of the question..:)
• 09-26-2003, 02:56 AM
philldresser
Jorge

I have been told by a reliable source from Ilford that to get the correct exposure on FP4 when under reciprocity failure conditions that you multiply the selected exposure time (in seconds) to the power of 1.49. So if you have a decent scientific calculator or an excel spreadsheet why not create your own table

Excel formula =POWER(A2,1.49) where A2 is the time in secs

Phill
• 09-26-2003, 07:09 AM
dr bob
Quote:

Originally Posted by philldresser
Jorge

Excel formula =POWER(A2,1.49) where A2 is the time in secs

Phill

That is close to the SQRT of 2 (1.41 et c.). I have been using that (SQRT 2) as a guidline for years. I discovered the same factor is useful in determining zone development times. Maybe a paper is in order? Ever notice the frequency of occurrence of this factor in photography and optics?
• 09-26-2003, 10:29 AM
Jorge
ah....Thanks Phil and Bob, seems like I could make a table that I could carry with this formula.....
• 09-26-2003, 12:17 PM
BobF
How about the Ilford site and the chart on page one for FP4plus?

http://www.ilford.com/html/us_english/pdf/FP4Plus.pdf

Is there something more you need? I seems to be such an obvious source that I must be missing something. Is new FP4plus a lot different than FP4?
• 09-26-2003, 01:10 PM
Jorge
The Ilford chart you mention is what I have used in the past with terrible results, and from what I understand I am not the only one. In addition it only goes to 30 seconds exposure. I am guessing the place I want to photographs will have soemthing in the 2 minute range for which I will have to compensate for reciprocity. While I am sure that FP4 and FP4+ would probably behave very similar at these exposures, when you are doing 12x20 it pays to be as accurate as you can...:)
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