reciprocity failure

Poohblah · Sep 1, 2008

i've always read that reciprocity failure is pretty bad for b/w films. in general, can i save a negative that was metered and exposed at 15 seconds or should i have compensated?

or does it depend a lot on the film i use (i really wish manufacturers printed reciprocity failure info on the box)?

according to this chart: Dead Link Removed
i could be off by anywhere from 1 stop to 4... should i be concerned?

Thomas Bertilsson · Sep 1, 2008

It depends on the film. TMax 100 and especially Fuji Acros are stable for long periods of time. Acros has no reciprocity adjustments until you meter two minutes.
Other films, like HP5+ start to taper off exponentially already at one second.

With regard to your film - look up the data sheet for the film you have and see how much you underexposed. Then find an appropriate development time, or use a 'Stand' development scheme where you can salvage some lost speed while taming highlights on other negs that might have been overexposed.

- Thomas

Poohblah · Sep 1, 2008

i was shooting pan 50 (i'm assuming it's similar to pan 100 as listed on the chart?) and unfortunately i mixed in 15 second exposures with 1/30 second exposures on the roll without really thinking about it... i suppose i could push to, say, EI 64 to try and get the most out of the entire roll.

basically the point of my original question was, is the latitude of b/w film so great that i can compensate for reciprocity failure on the enlarger in most cases? i'm developing the rolls tomorrow and i do want everything to come out okay. i'll find out the answer to my question soon enough, i guess...

btw what is the 'Stand' development scheme?

gainer · Sep 2, 2008

I suggest you look up "LIRF is Lurking at your F-stop" at www.unblinkingeye.com, written by some geek named Gainer. I don't think pushing will save it if it needs saving, but a number of modern films are an order of magnitude closer to true reciprocity than, say, Tri X of ten tears ago.

LIRF stands for "Low Intensity Reciprocity Failure" BTW. I'll try to find a copy of one of my charts and post it here. I think I did this once before.

gainer · Sep 2, 2008

I don't think you need worry much about correcting for reciprocity misbehavior. Delta 100 for example would have required only 4 added seconds, which is equivalent to less the 1/2 f-stop.

Murray Kelly · Sep 2, 2008

Gainer, what do you know about reciprocity failure at the other end of the scale? For latensification LEDs could be switched very fast. Where does film start to lose reciprocity at speed?

Murray Kelly

Thomas Bertilsson · Sep 2, 2008

Hi Pooblah,

Here is a link to the Ilford Pan-F+ product data sheet:
http://ilfordphoto.com/Webfiles/2006216115811391.pdf
I have attached the reciprocity curve for Pan-F+ to this message, and you will find that the frame in your roll that you metered at 15 seconds would have required 60 seconds, which means you exposed the film as if it were an ISO 800 film. Basically you underexposed by four stops.

If I were you I would focus on the correctly exposed frames and forget about this one, unless this particular frame is important to you and the other frames are not. Four stops is an awful lot, though, and it would be a compromise at best.

I have found that the best way to save underexposed negatives is by minimizing agitation and let the film sit in the developer for a very long time. But it is best to use a compensating developer such as Rodinal. Compensating means that it is designed to 'dampen' the development of the highlights, so to compress the tonal scale a little bit, while developing the shadows to full detail.

With stand development, you use your developer at high dilution, with Rodinal say 1+150. Agitate for the full first minute, then set the film tank down after you rap it hard on a counter top or similar (with a towel in between) to make air bubbles that stuck to the film during agitation dislodge and come to the surface. Then let the film sit for an hour without doing anything to it.

What this will do for you is it will take your 'normal' frames and develop
those 'normally' while frames that received less exposure will get a boost, and those that were overexposed will be held back to some degree.

Like all other developing schemes - there is no real magic bullet to salvage poor exposure. But this works pretty well to even out differences in exposures of say two stops. More deviation and even this technique will become a compromise. And you really should do some testing to see what can be done, perhaps by trying to duplicate the exposure situation you have now on another roll and try it at different dilutions and times to reach the best compromise between under- and overexposure.

What it boils down to is this - either you try to save the frame you underexposed by prolonging development (and it will be a compromise with poor contrast), or you develop the 'normal' frames like you always do and live with the failure.

I hope that helps.

- Thomas

BTW - Here's Gainer's article: http://www.unblinkingeye.com/Articles/LIRF/lirf.html

Poohblah said:
i was shooting pan 50 (i'm assuming it's similar to pan 100 as listed on the chart?) and unfortunately i mixed in 15 second exposures with 1/30 second exposures on the roll without really thinking about it... i suppose i could push to, say, EI 64 to try and get the most out of the entire roll.

basically the point of my original question was, is the latitude of b/w film so great that i can compensate for reciprocity failure on the enlarger in most cases? i'm developing the rolls tomorrow and i do want everything to come out okay. i'll find out the answer to my question soon enough, i guess...

btw what is the 'Stand' development scheme?

Poohblah · Sep 2, 2008

hey guys, thanks for the help. unfortunately the only developer i have access to is D76 at 1+0 (i use my school's darkroom and chemicals).

gainer · Sep 2, 2008

Murray Kelly said:
Gainer, what do you know about reciprocity failure at the other end of the scale? For latensification LEDs could be switched very fast. Where does film start to lose reciprocity at speed?

Murray Kelly

I know little about high intensity reciprocity misbehavior. It is a cause for concern when exposure time would be expected to be shorter than 1/1000 second, which is usually not encountered with low voltage electronic flash. A number of cameras now are capable of shutter speeds faster than 1/1000 second, so it might be worthwhile to do some experiments.

That's just a politician's (God forbid I should ever be one!) way of saying "I don't know.

ic-racer · Sep 2, 2008

Loss of reciprocity with short exposures.

(Copyright image reproduced for educational purposes).

This is what a series of H&D curves would look like if you stacked them end to end. Lines parallel to the slope "B" on the diagram would be typical H&D curves produced with progressively shorter and shorter times. The third parallel line (coming off the -2 on the Log t axis) represents an H&D curve that you could get from a rapid strobe exposure from an EG&G sensitometer. We can thank Harold Edgerton for elucidating this short exposure duration loss of reciprocity.

gainer · Sep 2, 2008

He was pretty much obliged to do so. He brought us into the use of electronic flash. In those days, the voltage used was on the order of 10,000 volts. We didn't have 10,000 mfd high voltage capacitors we could carry around. So, we can thank Edgerton for two things: electronic flash, and how to use it. Make that three. Add the stimulus to make the whole outfit so portable it can be built into a programmable 35 mm camera.

Poohblah · Sep 2, 2008

i pulled the negs out of the wash today and was pleasantly surprised when none of them were underexposed. i exposed one frame at f/32, 8 seconds, and the next at f/4, 1/8 second, but both exposures had exactly the same density. i wonder why?

ic-racer · Sep 2, 2008

Poohblah said:
i wonder why?

If there were no technical errors, you have demonstrated failure of reciprocity!

Poohblah · Sep 2, 2008

ic-racer said:
If there were no technical errors, you have demonstrated failure of reciprocity!

wait, what?

didn't i demonstrate the success of reciprocity? since f/32, 8 seconds, ASA 50 and f/4, 1/8 sec., ASA 50 are the same EV (unless i made a mistake in counting my stops)

MattKing · Sep 3, 2008

Poohblah said:
wait, what?

didn't i demonstrate the success of reciprocity? since f/32, 8 seconds, ASA 50 and f/4, 1/8 sec., ASA 50 are the same EV (unless i made a mistake in counting my stops)

f/32 @ 8 seconds = f/4 @ 1/4 seconds, if I count correctly.

By the way, in this particular comparison, ASA/EI/ISO doesn't factor in.

Matt

dancqu · Sep 3, 2008

Poohblah said:
wait, what?
didn't i demonstrate the success of reciprocity?
since f/32, 8 seconds, ASA 50 and f/4, 1/8 sec.,
ASA 50 are the same EV (unless i made a mistake
in counting my stops)

Putting it another way, you've apparently demonstrated
an absence of reciprocity faliure. At 8 seconds some
should be evident. Compare closely the very little
exposed areas of the negatives. Dan

Lee L · Sep 3, 2008

Actually f:32 8 sec is equal to f:4 1/8 second.

What you have demonstrated is that the generic Ilford curve doesn't apply for current production of HP5+, i.e. the failure of their reciprocity failure data.

In an article in Photo Techniques July/Aug 2003, Howard Bond carefully tested 5 films, including HP5+. He finds, as have many others, that the Ilford reciprocity failure curve doesn't match current films. His findings for HP5+

seconds
metered / use
1 / 1
2 / 2
4 / 5
8 / 10
15 / 24
30 / 54
60 / 156
120 / 345
240 / 19 min

So according to Bond's tests, your 8 second exposure was only underexposed by 1/4 stop relative to the 1/8 sec exposure, not something that would show clearly without very careful sensitometry.

Lee

Thomas Bertilsson · Sep 3, 2008

Lee thanks for posting those numbers. You said Bond tested 5 films, were any of them Plus-X, Tri-X, FP4+, or Delta 100/3200 by chance? If so, would you mind posting them?

It seems that Ilford pretty much use the same reciprocity curve for all of their films, which is interesting! I also studied Kodak's times, and it appears they post Plus-X and Tri-X to have the same reciprocity compensation at low speeds. The T-grain films have their own compensation factor, but still the same across the board except at really long exposures where TMax 400 tapers off faster than 100. What to think?

Fuji Neopan 100 Acros beats everything else by a mile and a half. +1/2 stop for everything metered from 120-1000 seconds. So if you meter can meter longer than 16 minutes, you're on your own... Hard to believe. I'll try to prove them wrong while I stay up late on the Lake Superior North Shore in a week...

I've shot some Delta 3200 yesterday, indoors - @ EI3200. It'll be interesting to see how my exposures at 2s and 4s come out, as I made no correction for reciprocity, and the chart says to at least double those times. I'm only one stop off, but on the same roll I have some 1/30th second exposures too, so I'll study the densities in the low values.

- Thomas

Murray Kelly · Sep 3, 2008

ic-racer, OK - thanks for that. I was vaguely aware that it started to fall down at 1/10,000 and that small leds are switchable at nsec speeds. Even at micro seconds it would, it seems, be possible to mount one in some sort of holder to fog a film enough to 'latensify' the images. I'm thinking of a jam jar, with the film wound around emulsion in, with an electronic switch on the LED inside, all in a black plastic jar (which I have) so's I don't have to fumble round in the dark for 60 mins.

The super bright LEDs don't fit the requirement on a quick google of characteristics, but the small ones could do it by careful selection. Since one is in no particular hurry, a measured quantity of sub-sensitive flashes could maybe work.

It appeals more to me than a half-hour of green light in a dark room!

Murray

gainer · Sep 3, 2008

Thomas Bertilsson said:
Lee thanks for posting those numbers. You said Bond tested 5 films, were any of them Plus-X, Tri-X, FP4+, or Delta 100/3200 by chance? If so, would you mind posting them?

- Thomas

Look at my article in Unblinkingeye. I analyzed Bond's data. The analysis included all the films he tested, some of which have changed in the meantime. These were Tri-X, TMY, TMX, HP5+, and Delta 100 IIRC.

What I found was that if you plot differences between measured and adjusted exposures against measured exposure on log-log graph paper, you get parallel straight lines. If you know the proper correction at any measured exposure, you have all you need to find the correction for any other time. I included the equation that you can use on most any pocket calculator. Only one constant changes with the film.

Lee L · Sep 3, 2008

Thomas,

I figure quoting one set of numbers is fair use, but I'm not sure that posting the entire data set would fall under that rule, and I don't want to put APUG in an awkward position. The films tested were Tri-X, Delta 100, HP5+, TMX and TMY. The back issue is available from the web site, Volume 24 no. 4., so you could go to the Photo Techniques web site and order the issue there.

Bond found that Delta 100 and HP5+, both nominally covered by the Ilford published curve, varied significantly from that curve and from each other. He found the Kodak films to differ from their published data as well. He also found that most of the films needed little to no reduction in development to reduce presumed contrast increases, which is in line with their generally better than published reciprocity characteristics. The article is a good read and very informative.

Anecdotal information I've seen from photographers supports Bond's findings.

Have fun along the north shore. I lived in Mpls for 6 years between '79 and '86 and made that trip on several occasions. Got 10 inches of wet snow between Duluth and Mpls on one trip back on April 30th. But summer fell on a Sunday that year, so we had a picnic.

I see Patrick popped in while I was writing. I don't have the issue with his follow up analysis of Bond's data, but search APUG for "reciprocity misbehavior" to find his formula, method, and a much longer discussion of reciprocity failure.

Lee

gainer · Sep 3, 2008

I should have stated that the constant for each film is the difference between the measured exposure and the exposure adjusted for reciprocity misbehavior at 1 second measuder exposure.

gainer · Sep 3, 2008

Lee, the very next issue after that has the same article I posted in Unblinkingeye.com analyzing Howard's data by a different method than he used.

dancqu · Sep 3, 2008

dancqu said:
Putting it another way, you've apparently demonstrated
an absence of reciprocity faliure. At 8 seconds some
should be evident. Compare closely the very little
exposed areas of the negatives. Dan

Within the area of lens coverage can be levels
of light which are within the domain of reciprocity
failure. That fact was not obvious to me when first
I had to deal with that failure. Just pointing it out
if not obvious to some others. Dan

Poohblah · Sep 3, 2008

i made a contact sheet today and there was a slight difference between the two frames, but it was no more than half a stop and certainly not anything to be worried about, so that matches the data that Lee posted.

dancqu said:
Within the area of lens coverage can be levels
of light which are within the domain of reciprocity
failure. That fact was not obvious to me when first
I had to deal with that failure. Just pointing it out
if not obvious to some others. Dan

so basically what you're saying is that i may have lost some shadow detail, say in zone I or II, due to reciprocity failure even if the midtones and highlights retained reciprocity?

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