Looooong Exposures on fp4/hp5

[coriana6jp]

Hi All,

I am about to start a project with fairly long exposures (several minutes or more) using most fp4+ & hp5+. The chart that Ilford provides is only good out to 35 seconds and the little infomation I found was beyond that Ec=Em^1.48 was the "correct" formula to use. Does this seem right?

Up until now, I have always used Acros for long exposures, but I want to dry a different look.

Any insight would be greatly appreciated.

Thanks!

Gary

 

[Lee L]

This post is a pretty direct answer from Ilford regarding your question about their data. (there was a url link here which no longer exists)

You have the correct formula for duplicating the Ilford recommendations, but people who have tested the films find the adjustments using Ilford's information to be significantly overexposed.

For more information, look for reciprocity failure threads here on APUG, there are a couple running now, and many older ones.

Howard Bond thoroughly tested 5 films (including HP5+) in 2003 and published this article with charts:
http://www.phototechmag.com/articles/articles/200705/0403Bond_Reciprocity2.pdf

Patrick Gainer did a follow up on that and a web version of his article is here:
http://www.unblinkingeye.com/Articles/LIRF/lirf.html
which gives a quick formula for closely approximating Bond's results.

For FP4+, using the Gainer formula, try a coefficient of 0.11476.
That would be: Ec = 0.11476*Em^1.62+Em

I'm basing this suggestion on data from testing of FP4+ reciprocity loss in astrophotography books. BTW, the books report FP4+ to have the same rate of reciprocity failure as Tri-X, so you could try Bond's Tri-X times for FP4+.

The Gainer formula coefficient for HP5+ is here on APUG in other threads.

People who have done much testing of reciprocity also report noticeable variation in the rate of reciprocity failure from one batch to another of the same film.

Lee

 

[Jim Noel]

Bond's adjustments are much more accurate than those by Ilford. Give them a try.

 

[Kirk Keyes]

You'll get less reciprocity on long exposures on fp4+ or hp5+ by using Fuji Acros. It has very good long exposure response.

 

[brianmquinn]

Also because their reciprocity is so good with really long exposures Fuji Acros or 100Tmax are actually FASTER the HP5+ or Tri-X.

 

[coriana6jp]

Thanks for the help, that was exactly what I was looking for and it provides a good starting point.

My main film for long exposures until now Acros, (only thing I can get locally), but am just trying for a different look than Acros provides.

Thanks again.

Gary

 

[jp80874]

Bracket by at least two stops and I always add an extra stop if it is after Thursday. Even if it is Wednesday, it is after a Thursday.

John Powers

 

[Jeff Bannow]

Bracket by at least two stops and I always add an extra stop if it is after Thursday. Even if it is Wednesday, it is after a Thursday.

John Powers

This is the official formula as taught to me by a wise man once ...

 

[Lee L]

The best fit Gainer formula coefficient for HP5+ is 0.12263 according to my regressions against the Bond data using QtiPlot. It's never more than 1/4 stop off from Bond's adjusted numbers, and when it errs, it errs toward more exposure.

I should probably add (although it shouldn't be necessary) that this difference is as likely to be experimental variation/error in the data as anything else.

Lee

 

[gainer]

Also because their reciprocity is so good with really long exposures Fuji Acros or 100Tmax are actually FASTER the HP5+ or Tri-X.

At what point do the curves cross?

 

[gainer]

The reason I asked that question is that the best fit to the Bond data for those two films plots as two parallel lines on log-log paper. The lines will never cross.

 

[gainer]

I have to admit to a rash statement. Oh, well. There's a first time for everything. If I use my own equation for reciprocity correction:
tc = tm^1.62*a +tm
where tm is the value of exposure time your light meter would read and tc is the exposure as corrected for reciprocity failure, and solve for tm1 where tc1 = tc2 when film 1 has ISO 400, a=.1 and film 2 has ISO 100, a = .01, I find that when tm1 = 25793.42 seconds and tm2 = 103173.68 seconds, tc1=tc2= 1427459 seconds. That is 396.52 hours, or 16.52 days. If you had a meter that would measure such a low light values, it would only be used for photographing coal mines at midnight, or scenes above the Arctic Circle at night time.

Films 1 and 2 are closely represented in the real world by HP5+ and some of the modern films. The a coefficient I found for TMX was about .05, and TMY was about the same. That means that TMY is definitely faster than HP5+ at any metered exposure > 1 second, but so also is Delta 400.