Zone system testing method

[Doremus Scudder]

Let's agree on the distinctions between ISO, ASA, DIN and E.I. just to avoid confusion. Yeah, we all know what we mean, but precision is a good thing, right?

ASA was the American Standards Association's method of determining film speed. The German equivalent, although expressed differently, was codified in the Deutsche Industrie Normen (DIN). These were subsequently harmonized and unified by the International Standards Organization (ISO) and uses both the earlier ASA speed and the DIN speed degrees (e.g., ISO 320/26° for 320Tri-X. Note the two speed designations, the first being the old ASA number and the second the DIN degrees). ASA and DIN are no longer used; they have been subsumed in the ISO speed rating.

ISO speed, like its predecessors', is determined with standard developers, development to a specific contrast gradient and a specific method of determining the speed point. This is all prescribed in the standard. The speeds so determined are good for comparing films (assuming they've been tested using the appropriate standards, some off-brands don't seem to be...) and as a starting point for deviation. Many find these speeds just fine. Note, however, that different developers than the standard ones used in the ISO testing can result in different effective speeds (Kodak notes this for their films and developer combinations) and that metering technique, equipment variables, etc. can necessitate using films at a different effective film speed than the ISO rating.

When one uses a film at a different effective speed than the ISO rating (or "box speed"), it is called E.I., or Exposure Index, which is a practical divergence from the norm for whatever reason. Many Zone System users work with a metering technique that works best when the film is rated around 2/3 stop slower than the ISO rating. Others "push" film by rating it faster, intentionally underexposing and compensating with extended development at the expense of shadow detail. Others simply find that they get better results at a different E.I. than box speed for whatever reason; developer, meter variances, shooting style, etc. etc.

So, when one is finding the effective film speed that works best for how they expose and process film, it should really be referred to as E.I. or effective speed. ISO, ASA and DIN really don't apply here.

Best,

Doremus

[Greg]

If one had to limit oneself to only one book on the ZONE System:

photography: CONTROL & CREATIVITY by T.L. Bollman and G. E. DeWolfe.

A small book published by Special Services, Rochester, New York 1972. The first part of the book (all of 28 pages) is EXPOSURE AND DEVELOPMENT FOR CONTRAST CONTROL IN BLACK-AND-WHITE PHOTOGRAPHY and covers a very simple method for ZONE System testing.