Firm speed greater than box!

[Tim Meisburger]

I finally got round to doing a film speed test for my peculiar combination: Shanghai 100, D-23, 85 degrees, and continuous agitation with a paterson orbital motor drive. As I often read about people who--without testing--rate their film at box speed, to ensure detail in the shadows, I fully expected my film to test out at EI 80 or 64. Instead I got 125!

Although this is on the surface counter-intuitive, It could be that the manufacturer simply made the same adjustment others do, and rated the film less than its actual speed to ensure usable density in the shadows. Or it could be my peculiar combination, or continuous agitation?

Should I shoot at an EI of 125, or be conservative and shoot at box speed?

Signed, Confused in Bangkok

[Heroique]

Should I shoot at an EI of 125, or be conservative and shoot at box speed?

Signed, Confused in Bangkok

Dear Confused in Bangkok,

Shoot both speeds in the field as part of your continued testing. See what really happens, and if it confirms your careful tests! Then, using your ever-deepening knowledge about your film, equipment, and darkroom habits, choose the speed that best serves your needs on a shot by shot basis. Let us know what happens, and if it’s possible, scan and share your results right here. BTW, I share your excitement about getting a slightly faster speed than box, for as we all know, it’s just too common for light in our business to be taken away, not granted!

Good luck, The LF Columnist :D

[Leigh]

Just shoot at box speed. That 1/3 stop won't make any difference in 99.9% of the subject details.

In the other 0.1%, the very slight extra exposure might bring up a cat's whisker that would otherwise be lost.

- Leigh

[Brian Ellis]

It's unusual but not unheard of for tested speed to be greater than the box speed. But the difference between 100and 125 is so insignificant with negative film that you could use either and it wouldn't matter. Years ago I used to make two exposures of everything, one at the metered exposure, one at one stop more to ensure shadow detail. Even with a full stop difference it almost never mattered, I could have made the print I wanted to make with either one.

[Tim Meisburger]

Okay. Thanks for the advice. Anyway, I'm happy to have the extra third of a stop in my pocket. I'm off on a trip in the morning, but when I get back my next task is figuring development times!

Cheers, Tim

[ic-racer]

It reads like you are actually doing what most would call an "exposure index" test rather than an "film speed test." An exposure index test can have any number result, but it only has a meaning with your equipment. If you are looking for problems, think of a slow shutter when you get an EI greater then the ISO.

[David Lobato]

if you compare a few light meters, they will vary by at least one third of a stop. I just tried two light meters myself this morning from two 35mm cameras, they differed by one third stop. It's possible a different light meter would give you box speed in your test. But the best part is you did the film speed test and there is no more guessing with your meter. That's what's important.

[vinny]

Omg!

[Stephen Benskin]

The first question that should be what are the testing conditions. How can anyone comment on the results without knowing the procedure?

The reason why most people who do Zone System testing where the speed point exposure is based on metering a target and stopping down 4 stops is generally produce slower EIs than the ISO speed is because the two methods use different ratios between the metered exposure point and the speed point. ISO uses 3 1/3 stops. That's a 2/3 stop difference. So methodology does make a difference.

[EdWorkman]

If your shutter speeds are right , enjoy 125
If your shutter speeds are wrong YOU get 125
hmphh, I learned 1/30, 1/60. 1/125 etc and 100 has since then seemed odd.
ISO requires very specific developer/time/temp.
An old, no really old, issue of Modern Photography had an article on ASA speed determination and concluded the specified D/T/T resulted in higher contrast than many folks would choose- it could have been/now might be called "overdevelopment".
But the folks that concocted Xtol [in Darkroom Tech or a fairly recent morph of it] say that a highly dilute developer IS capable of really getting 500 speed from HP-5+, measured fairly.

Thanks for sharing your results- real results are always better than photomyth,
ya just gotta be careful about the details so we can understand how to try it ourselves.

[Tim Meisburger]

For methodology: I shot a blank wall from one meter but focused on infinity. Stopped down four stops from metered value (pentax spotmeter) to give zone 1. As an initial test, using a mask I shot three quadrants on one sheet at: box speed, plus one third, and minus one third (leaving the fourth quadrant blank). I then gave the sheet normal development (for me) and when the negative was dry I metered the four quadrants looking for a one-third stop drop from the blank quadrant (which would be film base plus fog). As it happened I found that on this sheet so do not have to do a second sheet.

[Stephen Benskin]

An old, no really old, issue of Modern Photography had an article on ASA speed determination and concluded the specified D/T/T resulted in higher contrast than many folks would choose- it could have been/now might be called "overdevelopment".


The author misinterpreted the standard. While the approximate gradient of about 0.61 is slightly higher than the gradient for a grade 2 diffusion enlarger, it is about testing for speed and it's purpose is not about defining the overall film gradient but the shadow gradient. The standard in no way states that 0.61 should be considered normal development. The reason for this specific contrast is because when the contrast conditions are met, there is a good correlation between the fixed density method and the fractional gradient method. In fact the parameters are part of an equation that makes up the Delta-X Criterion. If the processing is outside the parameters, then the accuracy of simply using the fixed density of 0.10 no longer produces accurate film speeds. At this point, the Delta-X Equation needs to be used.

As the Delta-X criterion is just a simplified method of determining the fractional gradient speed, the resulting film speeds will be different than the fixed density method outside the ISO parameters. What we find with fractional gradient speeds, not being based on density but shadow gradient, is the film speed changes very little with changes in development making the slight difference between the gradients for speed testing and printing irrelevant.

80226

[Bill Burk]

And the ASA specifications, and Delta-X are both ways to find the 0.3 gradient, which is the ultimate goal - because 0.3 gradient is tied to the psychological tests of the first excellent print that can be made from a negative. 0.3 gradient is where you should place your (Zone 0?) deepest exposure, for any development time. But finding 0.3 gradient is mathematically intense - so these simpler diagrams were designed to make it foolproof to get there... Right?

[Steve Smith]

It's only 1/3 of a stop. I doubt that you can meter that accurately.


Steve.

[Stephen Benskin]

And the ASA specifications, and Delta-X are both ways to find the 0.3 gradient, which is the ultimate goal - because 0.3 gradient is tied to the psychological tests of the first excellent print that can be made from a negative. 0.3 gradient is where you should place your (Zone 0?) deepest exposure, for any development time. But finding 0.3 gradient is mathematically intense - so these simpler diagrams were designed to make it foolproof to get there... Right?

Right.

Steve, I agree. If Tim is using his meter to read the film densities, I would say a +-1/2 stop accuracy would be lucky.

Tim, my advice is to forget about film speed testing for now. Shoot using the ISO speed and see if it works for your style. What's more important is finding your development times. Do the testing and create some curves.

[Bill Burk]

I personally count on getting box speed with fresh film from Kodak.

But I don't set my meter to box speed. I pick my EI depending how I am going to meter and develop.

Simplest examples:

For incident metering, if I need the most speed, I will use box speed and develop as if aiming for ASA conditions.

For spotmetering, I place shadows on Zone II and develop to Zone System N times. Then I will use 2/3 stop less than box speed.

If I don't need the speed, I will leave ISO set at 2/3 stop less than box speed. I am comfortable working with that safety margin.

I will use Film Speed Test results... when I use expired film that doesn't achieve the printed speed.

Times I thought I was beating rated speed turned out to be test variables that needed to be better defined.

Even Todd-Zakia recommend that if you find only 1/3 stop speed increase... You cannot take this as significant evidence that you are getting higher speed. You should repeat the test and average the results to make sure it wasn't a standard deviation from real results.

[C. D. Keth]

omg!

wtf

[Tim Meisburger]

Thanks guys. I should repeat the test several times, but I'm not really too concerned with perfect accuracy. I just wanted to make sure I was not wildly off before I start testing for development times, which is my main concern. My current time is based rumour and inuendo. I heard D-23 is kinda similar to D-76, and that Shanghai is kinda like HP-4, then I used the Ilford temperature conversion chart to get times for average chemical temperature. Lot of guessing there, and I would like to do some curves and figure N, N+ and N-, mostly so I can deal with contrasty subjects better than I currently do.