film ISO testing for zone system--will this work?

Good morning all,

 

I bought a spot meter recently and a few boxes of t-max 400 film

(4x5). I am trying to determine the best ISO at which to rate the

film. Most of the tests on the internet say to meter the grey card,

then stop down either 2 or 4 stops to zone 3 or 1, respectively, and

then start taking test shots at 6 stops below this number by reducing

the shutter speed or aperature. The test negatives are then

evaluated a bit differently depending on whether you are trying to

find zone 1 or zone 3 exposure.

 

I practice, I have a hard time getting the right shutter

speed/aperature combination--my shutter (graflex supermatic) goes

from 60 to 100, then 200, etc., and iso 100 and 200 are not on my

light meter. If I use a shutter speed of 60, I have a hard time

finding a good aperature range that matches the light.

 

SO...my question is, why can't I just take a meter reading off of the

grey card (zone 5); stop down 4 stops to Zone 1; and then take 5 or 6

exposures at ISO 400, 320, 250, 125, 60; develop the negs, and then

rate my film at the iso that first produces a grey tint to the film?

This seems so much easier to explain and implement (to my simple

brain) that I can't figure out why I haven't seen it recommended

before. There may be a good reason for not using it, but I just

can't see how it wouldn't work. Am I being overly simple here?

Thank you in advance!

The point is to find out when your film/developer/process produces exposure .1 above filmbase+fog. Your explanation of how to get there is as good as any. It'll work fine.

If you read Minor White's excellent book on the topic, your approach is what he recommends, in part, in the section on his "Eye Match Method".

 

Your approach in only 1/2 of the solution. Next you'll get to figure out where Zone 7 or 8 is by varying your processing times after you've calcuated the film speed.

Thanks Hogarth, Christoper. I am glad to see that I was not off of my rocker with this.

 

Christoper, I think that the other tests I need to perform are the 'standard printing time' test, and the 'normal, plus, and minus development time' test--is that what you are referring to, or is there another test?

 

Thanks,

Doug

You get a lot more info from each test if you shoot a grey scale, such as the one from Kodak. I cut it in half, and taped it to a Kodak grey card. Like taking a dozen shots each exposure.

Jim, do you mean a print projection scale (the round pie-shaped scale)?

From memory, here's the process:

 

1) printing at a "standard" enlarge height, enlarger lens aperture, through processed film base, find the exposure that "just" produces pure black.

 

2) test for film speed by inspecting zones 1 and 2 for the first faintest step above pure black using constants revealed in step #1. Vary your exposure time +/- 10% and 20%.

 

3) test for development time by inspecting zones 7 and 8 against pure white (processed paper, unexposed). I think the steps of +/- 10% and 20% is good.

 

Repeat for expansion and contraction (N+ and N- processing).

 

I'm sorry if I've forgotten something. There are details too that I've not described. But you get the overall picture.

 

I hope this helps. Good luck. Its always fun to learn about this stuff. I used to shoot Ilford FP4+ at EI 250 because that's what my system demanded.

this all sounds good, but there is one thing I might add. You may want to get your shutter

speed checked before you go through all this trouble. Most leaf shutters may be +/- 1/3

at certain speeds. If you are going to sort out your effective ISO, you should start by

knowing the exact speed your shutter is working at. My 210mm, for example, shoots at 1/

36 when the indicated speed is 1/30. This is 1/3 slow. Good to know.

Good luck!

I don't think your description of what you've read on the web is accurate. You do begin by metering a gray card (or any other smooth surface) for a correct exposure using the manufacturer's film speed, and you do then stop down four stops to place the card on Zone 1. But you don't then make further exposures at six stops below this number. Either you're misunderstanding what you've read or you're reading a zone system testing methodology that I've never heard of before.

 

The way it's usually done is to meter the card and set your aperture and shutter speed to make a correct exposure using the manufacturer's film speed. Then stop down four stops to place the card on Zone I and make an exposure. Then set the film speed to double the manufacturer's speed, meter the card and set the aperture and shutter speed to make a correct exposure at that film speed, stop down four stops, and make a second exposure. Then set the meter to half the manufacturer's speed, meter the card and set your shutter speed and aperture to make a correct exposure at that speed, stop down four stops, and make a third exposure. Go through this routine a couple more times with different film speeds in between half and the manufacturer's speed so that you end up with about five exposures, one at the manufacturer's speed, one at twice that speed, one at half that speed, then a couple others in between. Obviously you have to keep track of which negative was made at which speed. Then develop the negatives and proceed from there to determine the correct Zone I exposure with a densitometer or with one of the eye ball methods if you don't have access to a densitometer.

 

While I said to set the aperture and shutter speed for each exposure, actually you should begin with an aperture sufficiently wide open so that you can make all five exposures by changing only the aperture. Changing shutter speeds introduces an unwanted variable since shutter speeds are more likely to be off than apertures.

 

IMHO you should be aiming for a Zone I exposure, not a Zone III exposure. Testing for your personal film speed is the first step in zone system testing. You do it before you've done your development time test. So you don't yet know your normal development time, you're just using the manufacturer's suggested times. Since you don't yet know your normal development time, you should make exposures that are affected as little as possible by development. Zone I is virtually fully developed about a third of the way through the total time. Additional development beyond that point has no effect on Zone I as a practical matter. So by using Zone I as your goal you've removed development time as a factor in determining which of your five or so exposures is the right one. Zone III on the other hand is somewhat more sensitive to development time and will be affected by the total time more than Zone I. The difference may not be great but since it's just as easy to shoot for Zone I as Zone III, and since Zone I is less sensitive to development time than Zone III, why not use Zone I?

Andrew-

 

Your suggestion is a good one. However, the idea of doing a film speed test is to find the correct film speed for your particular film-meter-lens-developer-lightsource combination. This inherently is going to "correct" for a shutter which is consistently off by 1/3-stop, just as it would correct for a meter which is off by 1/3-stop.

 

One note to you Doug: your method is sound except for the idea that you are testing film speeds that are one whole stop apart. A much more accurate procedure would be to expose the film at Zone I for 3 speeds above and 3 speeds below the rated speed. So, if you're film is rated at 125, you would test for 64, 80, 100, 125, 160, 200, and 250. It's not uncommon that the difference between the rated speed and your "correct" speed is only 1/3-stop.

 

And don't forget that your film speed is correct only for the light source you made the test with. If, for example, you test outside in daylight, the speed may not be correct for fluorescent or tungsten lighting and vice versa.

Thanks all, this is all very helpful. My lens shutter is off by up to 1/2 stop at 1/15 and slower, my repairman could not test the focal point shutter with his equipment. I have never used it and the iso test should factor in the 1/2 stop speed difference in my lens shutter. It's a bummer that you can't test in tungsten light (for outdoor landscape use) since I work during the week and that means that I have to test around noon on the weekend, when I want to be shooting more than a grey card. Thanks to everybody for their help, i will definitely implement the suggestions into my test.

Doug,

 

all the methods described up to now have a common flaw: they measure a grey card under conditions that ordinary photography would not use as a target for Zone 1. You should note that the color of light and reflexivity of the grey card bias the measurement to a significant degree. What you should do is take a reading of the grey card in open shade and place that reading on zone 1. Only then will you get a measurement relevant for measuring typical zone 1 motives.

 

I hope this helps.

Emil