Reciprocity misbehavior.

[Bob F.]

For those who prefer numbers to charts, some selected numbers using Pat's formula & tc,1 values.

[CODE]METER TMY 400TX TMX HP5+ 100Delta
TIME
1 1.1 1.2 1.1 1.1 1.0
2 2.2 2.5 2.2 2.3 2.1
3 3.4 4.0 3.4 3.6 3.3
4 4.6 5.6 4.7 5.0 4.4
5 5.8 7.3 5.9 6.4 5.6
8 10 13 10 11 9
10 13 17 13 14 12
15 20 29 21 23 19
20 28 42 29 33 26
30 45 72 47 55 41
40 64 107 67 80 58
50 84 146 89 107 76
60 106 188 112 137 95
90 179 338 191 238 157
120 262 515 281 356 227
180 455 941 491 635 387
300 928 2041 1011 1341 774
600 2532 5952 2785 3798 2057[/CODE]

Cheers, Bob.

[fhovie]

I think these numbers are low. - I have exposed a lot of TRI-X, metered at 5 sec and exposed correctly at 10. Metered at 10 and exposed for 30. Of course metering is not that good in low light - It quickly becomes - open it up for a minute or 5 .....

[MikeK]

I found my source of development adjustment times on the Kodak Site:

Kodak Technical Publication E-31 July 2002

Exposure and Development Adjustments for Most Black & White Films

Indicated
Exposure Development
Time Adjustment

1/1000,000 +20%
1/10,000 +15%
1/1000 +10%
1/100 None
1/10 None
1 -10%
10 -20%
100 -30%

A tad out of date as some of the films mentioned are no longer with us So it would probably be worth carrying out a few tests to see if these development time adjustments are applicable for the more modern versions.

- Mike

- Mike

[Lee L]

I do, however, carry around a piece of paper in my wallet that says:

TMAX100 MeteredTime ExposureTime Dev
4 5 N
8 14 N
15 27 N-1/2
30 60 N-1
60 150 N-1
120 360 N-1.5
4min 15min N-2
3min 35min N-3
15min 1hr15min N-3

Which I think I copied from somewhere here. This seems to work. I'm not sure if it graphs to a straight line though. Would this be in line with what has been described so far?

Thanks,

Will

Well, here's a graphical answer to your question, on linear rather than log axes if you're more comfortable reading them as curves. This graph is a comparison of Will S.'s "data" listed as Recommended, Gainer's calculations from the Bond data with the derived TMX factor of .069, and the traditional Schwarzschild formula using Robert Reeves' test results for a Schwarzschild exponent of 0.81 .

If you read this simply, you might get the _mistaken_ idea that this somehow discredits Gainer's and Bond's work, but that is certainly not my intention, nor necessarily the case. The closer fit between the Schwarzschild calculations and the "data" you have in hand is most likely a reflection of the fact that the numbers you have were generated using the Schwarzschild formula to generate numbers that are a close fit to some unknown number of test observations. I've never seen any description of the exact method used by the manufacturers to determine reciprocity adjustments. Maybe someone on this list knows. I'd be interested in hearing about it. Since Mr. Bond is a meticulous worker and Mr. Gainer's calculations are such an excellent fit to this published data, I see no reason to consider their work as anything less than accurate.

In any case, within the range of exposures tested and recommended, there is no more than about a 1/3 stop discrepancy between the two methods of calculating an adjusted exposure time. That's not a very significant practical difference given the vagaries of meters, shutters, etc.

Lee

P.S. I converted the typo "3min 35min N-3"
to "8min 35min N-3" for my calculations and graph.

[PieterB]

Incidentally, it is interesting just how many avid photographers here have metioned they are also musicians - quite a few!

Well, two people of my family play music as well, and they're also interested in photography. I think it has something to do with creativity.

"Blockflute" in Germany is 'blokfluit' here in Belgium.
I'm not good in German either, so I don't know where the 'umlaut' (special character) belongs. Worldlingo gives me "Blockierensystem Flöte" But I think that's not correct

[rjr]

Pieter,

it´s "Blockfloete"/"Blockflöte". 8-)

[Will S]

Well, here's a graphical answer to your question, on linear rather than log axes if you're more comfortable reading them as curves. This graph is a comparison of Will S.'s "data" listed as Recommended, Gainer's calculations from the Bond data with the derived TMX factor of .069, and the traditional Schwarzschild formula using Robert Reeves' test results for a Schwarzschild exponent of 0.81 .

Thanks Lee! You were right about the typo of course.

Will

[Bruce Osgood]

SNIP.....
Due to the fact that the factor 1.62 works for these diffeent films of different manufacturers, it is my opinion that it will work for any current emulsion to acceptable accuracy. That is to say that I expect it to be within the spread among readings of indicated exposure made by a number of proficient photographers of the same scene. If this is the case, all one needs to know is the reciprocity correction to one indicated exposure to find the correction for any other indicated exposure. ....end snip

So, after all the graphs and charts are drawn is it not true that a metered exposure of 10 seconds can be be multiplied by 1.62 to become 16.2 seconds and a 100 second exposure becomes 162 seconds? I don't really need a graph or chart for this do I?

[fhovie]

So, after all the graphs and charts are drawn is it not true that a metered exposure of 10 seconds can be be multiplied by 1.62 to become 16.2 seconds and a 100 second exposure becomes 162 seconds? I don't really need a graph or chart for this do I?

It is not linear -For TRI-X, based on Kodak pub F4017, if the EV indicates a 10 second exposure, the correction is +2 stops - or 40 seconds - with a 20% reduction in development. At an EV indicating 100 seconds the corrections is 3 stops or 13.3 Minutes with a reduction in development of 30%. Even a one second exposure is supposed to be at +1 stop. (I generally don't start correcting till there is an indication for 2 sec or more.)

[Bob F.]

So, after all the graphs and charts are drawn is it not true that a metered exposure of 10 seconds can be be multiplied by 1.62 to become 16.2 seconds and a 100 second exposure becomes 162 seconds? I don't really need a graph or chart for this do I?

No, sorry, that is not the case. Look at the equation again: there is a value (different for each film) called tc,1 which is the adjustment for a 1 second exposure (found by experiment) for that particular film. That value needs to be plugged in to the equation to get the final time.

Cheers, Bob.