I saw the following exchange on another forum and am confused by the answer (i.e., it seems to conflict with other things I have read and seen). Is the answer entirely correct?

Question:

As I understand it, Ansel Adam's "Zone System" was originally developed for black and white film. As I understand it, there are ten zones corresponding to 18% gray (zone 5), then zones 0-4, and 6-10. Each zone corresponding to 1 stop above or below the previous.

When color slide film is noted to have "3 stop latitude", does that mean that it can represent, say, Zone 5, then zones 2-4, and zones 6-8? or does that mean it can only reproduce zones 4,5,6?

Answer

I'm going to get myself in a LOT of trouble with this answer, but here it is, anyway:

Zones canNOT be stops, and here is why. An 18% surface is called that, because it reflects 18% of the light that falls upon it. Zone V.

Opening up one stop DOUBLES the light that hits the film, and records on film as a surface that reflects 36% of the light that falls upon it. Zone VI.

Opening up another stop results in an image of a surface that reflects 72% of the light that falls upon it. Zone VII

Opening up one more stop records on film as a LIGHT BOX! Or DAYGLO! 144%!! That is as opaque as the negative can get. And we're only at Zone VIII! Therefore, Zones are not equivalent to stops.

I understand that you can pretend that they are, and that this pretending can be useful; but Zones are not stops, as shown above.

The Zone System is all about EXPANDING and CONTRACTING tones in the scene, so that the print will have sufficient contrast, or so that as wide a range of tones, light to dark, as possible can be "fit" onto the paper.

It's a problem of terminology and definition. A stop is a halving, or a doubling of the amount of light that is allowed to hit the film. That's all.

What a Zone is depends on when and where. I don't pretend to be an expert on the Zone System. But I think I'm safe in saying that there are zones in the original scene. There are zones as "placed" on film. Zones as determined by how we develop the film. And zones determined by how we print that negative. To equate Zones with Stops is to oversimplify, and mislead.

-- Chris Werner (cbwerner@att.net), October 30, 1999

Answers

This persons answer is a misinterpretation of the zone system. According to this if you went outside on a bright sunny day the brightest thing possible would be less than zone VIII but in the world that I live in zones X, XI, XII and XIII exist. The zone system is about previsualizing an image and to do so you calibrate your exposure and development to accomplish this. The above explaination of how light works is oversimplified, it is about intensity of light reflected not reflectivity of the object.

-- Jeff White (zonie@computer-concepts.com), October 30, 1999.

Yes, the answer given was not entirely correct, to put it mildly. As someone correctly pointed out later in that thread, a subject zone is essentially the luminance ('brightness') of the object, and this depends on both the light received by the subject (the illuminance), and how much of this light is reflected by the subject.

Of course, some objects (such as the sun) actually create light, and we can measure the luminance of such objects, so these also fall into zones.

-- Alan Gibson (Alan.Gibson@technologist.com), October 31, 1999.