J&C Classic-400 Reciprocity ???

dr bob · Jul 22, 2005

Initial tests of 4x5 Classic-400 film has yielded an unexpected result:

Pacemaker Speed Graphic w/ 150/5.6 Linhof Symmar-S
Setting; f/8 @ 1/8 and 1/4 sec. (Zone V patch indicated f/8@1/8)
Process; HC110(b) 7 min, Ilford fixer(film), 8 min
Target; CRT display as described in article on spot metering densities

Both negatives are almost identical. The Zone III patch on the 1/4 sec. shows a very slight increased density over the 1/8 sec. negative but the difference is not measurable with my technique. It should be at least twice as dense - yes?

Is it possible that J&C Classic-400 is in reciprocity failure at those shutter speeds? The shutter calibration is not exact but the two are about a factor two different. I cannot think of any other explanation.

David A. Goldfarb · Jul 22, 2005

That's curious. I would have expected to be about the same as other traditional films.

Have you tried with a different shutter (or same shutter/different film), just to be sure?

dr bob · Jul 22, 2005

David A. Goldfarb said:
That's curious. I would have expected to be about the same as other traditional films.

Have you tried with a different shutter (or same shutter/different film), just to be sure?

Tri-X, PXP, TMY and FP4 all perform as expected using the same or equivalent processing. I'm sure the shutter is operating properly. Plans are already in effect to employ a different lens for an alternate approach. Thanks David.

magic823 · Jul 22, 2005

dr bob said:
Initial tests of 4x5 Classic-400 film has yielded an unexpected result:

Pacemaker Speed Graphic w/ 150/5.6 Linhof Symmar-S
Setting; f/8 @ 1/8 and 1/4 sec. (Zone V patch indicated f/8@1/8)
Process; HC110(b) 7 min, Ilford fixer(film), 8 min
Target; CRT display as described in article on spot metering densities

Both negatives are almost identical. The Zone III patch on the 1/4 sec. shows a very slight increased density over the 1/8 sec. negative but the difference is not measurable with my technique. It should be at least twice as dense - yes?

Is it possible that J&C Classic-400 is in reciprocity failure at those shutter speeds? The shutter calibration is not exact but the two are about a factor two different. I cannot think of any other explanation.

I usually don't see reciprocity failure till about 1 sec. Never at 1/8 or 1/4. I've never used J&C 400 (just 200)

Steve

Alex Hawley · Jul 22, 2005

dr bob said:
Is it possible that J&C Classic-400 is in reciprocity failure at those shutter speeds? The shutter calibration is not exact but the two are about a factor two different. I cannot think of any other explanation.

I wouln't think so Dr. Bob. I routinely run J&C 400 down at 1/5 or 1/10 second with f/32 or f/45.

Even down in the reciprocity range, I've found J&C 400 can handle it: This one was taken at f/32 with an exposure of 48 seconds: (there was a url link here which no longer exists)

David A. Goldfarb · Jul 22, 2005

You're sure the shutter hadn't been sitting for a while unused, so maybe the 1/8 sec. exposure would have been a little slow, and the 1/4 sec. exposure was correct, but after that 1/8 would have been okay?

gainer · Jul 22, 2005

dr bob said:
Initial tests of 4x5 Classic-400 film has yielded an unexpected result:

Pacemaker Speed Graphic w/ 150/5.6 Linhof Symmar-S
Setting; f/8 @ 1/8 and 1/4 sec. (Zone V patch indicated f/8@1/8)
Process; HC110(b) 7 min, Ilford fixer(film), 8 min
Target; CRT display as described in article on spot metering densities

Both negatives are almost identical. The Zone III patch on the 1/4 sec. shows a very slight increased density over the 1/8 sec. negative but the difference is not measurable with my technique. It should be at least twice as dense - yes?

I'm not grasping why one would expect a 1 stop difference in exposure (log difference of 0.3) to give double the density with the same development. What was the average gradient? Even at a gradient of 1.0, the difference in density should only be about 0.3.

lee · Jul 22, 2005

what I am not clear on is why are you starting at 1/4 and 1/8? I would think the reciprocity failure would kick in after 1 second not in the range you started in.

lee\c

David A. Goldfarb · Jul 22, 2005

dr bob said:
...

Target; CRT display as described in article on spot metering densities

...

I cannot think of any other explanation.

Flicker? I wouldn't test with a CRT display.

Donald Qualls · Jul 22, 2005

CRT flicker should be high enough frequency not to bother an exposure as long as 1/8 second (he said, starting from the bottom).

However, it would be much more conclusive to shoot two negatives of identical luminance targets with aperture changed along with shutter, to give the same nominal exposure. Reciprocity failure is related to light intensity, not to actual exposure time; else exposing twice as long at the same EV and aperture might be expected to result in less density in films with high Schwartzchild exponents used outside their reciprocity limits (this is what, in logic, is called reductio ad absurdum). If twice the exposure time at half the light intensity (with other factors controlled) doesn't give the same density, then you have reciprocity failure.

Many conventional (i.e. hexagonal or cubic grain) films show reciprocity failure from 1/2 second, a few from 1/10 (exposure calculated for Zone V, generally). What we see above, however, is more likely indicative of intermittent shutter problems calling for a CLA, or inconsistent development, or monitor brightness variation due to line voltage, temperature, etc., or even film from two different emulsion batches (with different speeds) than of anything related to Schwartzchild effect.

dr bob · Jul 22, 2005

Alex Hawley said:
I wouln't think so Dr. Bob. I routinely run J&C 400 down at 1/5 or 1/10 second with f/32 or f/45.

Even down in the reciprocity range, I've found J&C 400 can handle it: This one was taken at f/32 with an exposure of 48 seconds: (there was a url link here which no longer exists)

Alex: I have admired your images out on the prairie for years. Its good to hear from someone who has had experience with this film. Prepare for PMs 

David A. Goldfarb said:
You're sure the shutter hadn't been sitting for a while unused, so maybe the 1/8 sec. exposure would have been a little slow, and the 1/4 sec. exposure was correct, but after that 1/8 would have been okay?

I am quite sure the shutter was working properly. Before I make an exposure I always operate the shutter at the selected setting a few times.

gainer said:
I'm not grasping why one would expect a 1 stop difference in exposure (log difference of 0.3) to give double the density with the same development. What was the average gradient? Even at a gradient of 1.0, the difference in density should only be about 0.3.

The target values were arranged in one-stop intervals. I certainly did not expect a one-one correlation. However, there was not even a 0,1 stop difference in the Zone V patch.

David A. Goldfarb said:
Flicker? I wouldn't test with a CRT display.

At 1/8 and ¼ sec. I doubt CRT flicker is a problem. A total drop in luminance might but to have that be exactly one stop seems incredible.

gainer · Jul 22, 2005

You did not say what your method of measuring density is. I repeat: I do not see how you can deduce reciprocity effects from the data you provided. There is no good reason to expect the densities from two exposures 1 stop apart when both negatives are given the same development, even if there were no such thing as reciprocity non-linearity.

So-called reciprocity failure begins at some very short exposure time and increases both ways from there. The equation I have found by analyzing all the data I can find is:

Tc = Tm + a * (Tm ^ 1.62)

This equation reads "The exposure time corrected for reciprocity non-linearity is the sum of the measured time, Tm, plus the constant "a" times the quantity Tm raised to the 1.62 power."

The only part of that equation that varies significantly from film to film is the coefficient "a". The greatest value of "a" that I have seen is 1. The current 400TX is about 0.18. HP5+ is about 0.11. TMX and TMY are about equal at 0.6.

You see from the equation that the reciprocity correction only approaches 0.

gainer · Jul 22, 2005

Donald Qualls said:
Reciprocity failure is related to light intensity, not to actual exposure time; else exposing twice as long at the same EV and aperture might be expected to result in less density in films with high Schwartzchild exponents used outside their reciprocity limits (this is what, in logic, is called reductio ad absurdum). If twice the exposure time at half the light intensity (with other factors controlled) doesn't give the same density, then you have reciprocity failure.

.

The problem here is that you failed to take into account the fact that film is absurd. Sorry, couldn't resist. Certainly the light intensity enters the consideration, but the problem usually solved by reciprocity corrections is how to maintain the same density when it is required to change the f-stop. The usual light meter's calculator dial gives an estimate based on the light it measures. Over what range of exposure times is that estimate good? Certainly, the proper exposure time is related to the illumination at the film plane, but we know it is not the linear relationship used by the meter. Once you have determined the exposure time from the meter readings, the illumination no longer enters the calculations we can do. From that point, the exposure time calculated by the light meter is the only input required to calculate the required exposure time provided you know the value of "a" for the film at hand.

gainer · Jul 22, 2005

gainer said:
TMX and TMY are about equal at 0.6.

QUOTE]
Oops! 0.6 should be 0.06. 100Delta is slightly lower. APX 100 is lower yet.

Alex Hawley · Jul 22, 2005

dr bob said:
Alex: I have admired your images out on the prairie for years. Its good to hear from someone who has had experience with this film. Prepare for PMs 

Thank you most kindly Dr. Bob. No guarenteed answers here but bring on the PMs.

dr bob · Jul 23, 2005

Patrick et al.: The question is not the value of a possible reciprocity effect but whether or not the phenomenon is even present in this case. There is a possibility that I made some other error in exposure or processing. I approximate densities with my Minolta spot meter as described in the article on that subject (you reviewed it once when I submitted it to Photo Techniques before they went d----l.) I need no sophisticated measurements, as I do not employ the Zone system in its extreme.

The object of my experiments is to determine my EI for this new-to-me 4x5 film. One quick method is a visual comparison with a wedge. A superficial look into this technique yields an EI of about 50, which is ridiculous for a 400-rated film. I repeat that the equipment and technique was identical to that used for PXP, Tri-X, TMY, HP5, FP4, and EFKE 100R. These films rated at or just below the manufacturers rating. Ex., Tri-X 320 rates at EI=200. But the fact remains that an attempt to double the exposure by halving the shutter speed resulted in essentially no change in density in any of the patches on the target.

I shall surely repeat this test with closer attention to controls and maybe with the lens at the maximum aperture f/5.6, or even with another faster lens. This should give a Zone V exposure time of 1/15 sec. (CRTs have a deceptively low luminance). Then I should have more margin.

Thanks to all for your input and advice.

gainer · Jul 23, 2005

Now that I have shot my wad on reciprocity, let me ask: has the spot meter you are using a digital or analog readout?

Digital meters may be of two types. One is simply an analog to digital converter on the end of an analog sensor and computer. I have built these. The analog sensor-computer consists of a linear photosensor which provides a current proportional to the illumination followed by an op amp with silicon diode feedback. The output of the op amp is proportional (over a wide range) to the log of its input. The a-d converter is built into a digital panel meter.

The other type periodically samples the illumination and sends the sample to a computer whose output is in digital form.

When you are sampling an intermittent light source, a lot depends on where the sampling takes place and on how long it takes to compute the logarithm. In measuring the light from a TV screen or equivalent, the repetition rate also enters into the result.

As to how much change in density to expect from doubling the exposure time, certainly the local slope of the characteristic curve enters the equation. You haven't said what that slope is or was expected to be. I have no idea what the slope should be for this film and development, but I'll wager that it is is less than 1 over the major part of the range. A 1 stop change of exposure with normal development would be expected to produce no more than 2/3 stop change in density reading. What contrast index would you calculate from your measurements?

From what I have seen of both modern and ancient films, reciprocity misbehavior could not cause what you are observing.

dr bob · Jul 23, 2005

Patrick: I shall take this to a PM with your permission.

dr bob · Aug 4, 2005

Hello again. The mystery is solved sort of. I ran a test on my HC110 and found it lacking. It was old but not too old and I always used it one-shot so it wasnt depleted through use. Never the less it would not perform. A new batch boosted the development to an appropriate density and slope.

However it looks like I will have to use an EI of 200 (or slightly lower) to get the performance I desire. This is certainly not unusual at all. More tests are in progress but no more data will be submitted until Im sure things are going right, Sorry.

Alex Hawley · Aug 4, 2005

Glad there was a logical explanation for it Bob. One doesn't usually think of HC-110 going South due to age. Just for data purposes, how old was it?

Donald Qualls · Aug 4, 2005

Alex Hawley said:
Glad there was a logical explanation for it Bob. One doesn't usually think of HC-110 going South due to age. Just for data purposes, how old was it?

And how was it stored? I've got a liter of the stuff, near enough, divided up in small glass containers and the current working portion stored in plastic bottles; this is of interest. The last bottle, a pint, lasted just over a year, divided up in 4 ounce plastic bottles so only one was exposed to air at any time.

dr bob · Aug 5, 2005

Donald Qualls said:
And how was it stored? I've got a liter of the stuff, near enough, divided up in small glass containers and the current working portion stored in plastic bottles; this is of interest. The last bottle, a pint, lasted just over a year, divided up in 4 ounce plastic bottles so only one was exposed to air at any time.

The stock developer used had been sitting about in a glass, stoppered container in a cabinet away from light and heat for about 6 mo. I prepared it from the syrup at that time. I've never had a problem with this stuff stored up to a year prior to this experience - I shall not try to preserve it this way again but always make it up from syrup each time - no sweat. OBTW, the concentrate is over two years old and very OK!!!! (See recent posts by Gainer on this subject.)

Divided storage is an excellent means of preserving developer of various types. E.g., I divide my D76 in several pint (chemical) bottles well stoppered and completely full. They will last well for at least 6 months that way. I have also reused D76 by pouring it back into the bottle and making up the slight loss by carefully dripping in distilled water to fill it. Developers are so cheap, it really doesnt make sense to compromise ones work through a false economy.

This will be my last report on this subject unless additional mysteries erupt!

Donald Qualls · Aug 5, 2005

Oh, it was *stock solution* that went bad. Whole other deal compared to the syrup, yes indeed. I don't recall that being made clear at any previous point. Yes, the stock solution has a shelf life, in partially full bottle, of about three months plus some uncertainty. I only make up a few ounces of stock at a time, since I use it only when I want a small amount of high dilution, as when souping microfilim in two ounces of Dilution G in my homemade tank.

dr bob · Aug 6, 2005

Donald Qualls said:
Oh, it was *stock solution* that went bad. Whole other deal compared to the syrup, yes indeed. I don't recall that being made clear at any previous point. Yes, the stock solution has a shelf life, in partially full bottle, of about three months plus some uncertainty. I only make up a few ounces of stock at a time, since I use it only when I want a small amount of high dilution, as when souping microfilim in two ounces of Dilution G in my homemade tank.

Sorry didnt mean to sound nefarious. Yes it was old stock. But this is the first time I had problems with using the stuff in imprecise (quick-and-dirty) tests. I NEVER use old developer on non-reproducible negatives. I will do additional detailed tests to nail down the soup time for HC110. D76, and Rodinal. I dont see using this film in D23 or divided development at this time maybe later. Id much rather make images.

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