Defining one's personal ASA for a film : LUSENET : Large format photography : One Thread

I've been reading Ansel Adams' book "The Negative" in which he explains how to determine one's personal film speed given one's equpiment and developing technique. His described process calls for a densitometer. I have to admit that I am lacking access to a densitometer, so I am wondering what other ways are there to determine one's personal film speed for Zone system work/applications.

Any suggestions on other resources I should look at to determine film speed?

Thanks, Robert

-- Robert Ruderman (, May 14, 1998


Robert, Your last question first.

In addition to Adams' wonderful book, The Negative, look at Fred Picker's book, The Zone VI Workshop. Picker's discussion of the Zone System, and his instructions for determining one's personal film speed, are excellent and very well illustrated. Steve Simmons' View Camera book also has good, sensible information on determining one's film speed, and the subsequent use of the Zone System. (BTW, why does everyone hate Fred Picker so much?) If you're only interested in determining your personal film speed, ONCE, to expose and produce a Zone I density (approximately between .08 and .12 above film base fog), you might call your local photo lab, professional photography studio, or any nearby college photo schools/departments. Most reasonably well-equipped labs have a transmission densitometer available, and can quickly read your test negatives to determine densities. Just be sure you have them take a reading from the clear portion of the film area as well, to determine film base fog density.

Now for the long-winded stuff...forgive me, for I do tend to run on:

Kodak sells a very useful device: Product # 1523380, 1-A 11-step uncalibrated step tablet. Calumet sells it for $54.95. I've used it for years, to zero-in my densitometer dial needle to a predetermined density reading, whenever I turn on the unit. These densitometer units tend to "drift" over time, so it's best to establish a known reference point every time you use one.

This Kodak step tablet is simply an 11-step, sequential series of carefully exposed (in a sensitometer) and developed negatives, on Kodak film stock. The 11 sequential negative densities range from 0.05 density (step 1) to 3.05 density (step 11), in perfectly spaced 0.30 density increments. (Kodak also sells a 21-step tablet, with more tightly-spaced density steps. It's more expensive.) The first five steps of the 11-step step tablet, densities 0.05, 0.35, 0.65, 0.95 and 1.25, would be most useful for your B&W film tests, since they correspond to several important Zone densities.

I have found it quite easy, and reasonably accurate, to place the step tablet on a light table and match it to test negatives by eye. It's surprising how sensitive your eye is to slight differences in densities. Also, if you have a spotmeter, you can use it to make comparison readings between the known step tablet density and the negative to you wish to measure. While this does not replace a densitometer reading, it can be a reasonably accurate substitute.

If you want to continue your Zone System testing, this same step tablet can also be used to measure and compare other zones, in a similar fashion, to determine your development temperature/agitation/developer dilution/times for the higher Zone densities. For example, if the density range of a typical negative would be from about 0.80 density to 1.25 density, with a middle Zone V density of aproximately 0.65, the step tablet has accurate density examples of 0.65 and 1.25 for comparison.

I hope this helps. I also hope this discussion does not elicit the usual Zone System controversies. If you have any specific questions, please e-mail me directly.

Good luck, Sergio.

-- Sergio Ortega (, May 15, 1998.

Correction: sentence in 2nd to last paragraph should read: "the density range of a typical negative will be about 0.80 to 1.25 , depending on the type of enlarger used to print it". Sorry!

-- Sergio Ortega (, May 15, 1998.

Or make your own densitometer, with a spot meter and a close-up lens. Put the negative on a ligh-box, and directly meter the parts of the negative. Each stop on the meter is a density shift of 0.3.

-- Alan Gibson (, May 22, 1998.

A practical rather than scientific way is:

Print half of a clear negative (and half no hegative) at various exposures to determine the minimu exposure with that film base + fog density to produce maximum black (where the part thru the negative matches the part with no negative).

Do trial exposures at 1/3 stop intervals for zone I (4 stops less than medium gray). For example, with a film which is nominally ISO100 try zone I exposures ranging from an EI of 25 to 100 at 1/3 stop intervals.

Contact print each negative next to a clear (unexposed but developed) negative. The EI at which you just notice a difference between the pure black from the clear negative and the test negative is the correct EI to produce correct shadows

-- John Lehman (, May 22, 1998.

Moderation questions? read the FAQ