The exposure meter is calibrated to register a light intensity and indicate an exposure value which will render it as a middle grey tone (Zone V on the nine value Zone System Scale, or the value of the 18% reflectance Kodak grey card), when the film is developed according to manufacturer's specifications.
In other words, whatever value you read with an exposure meter, be it a dark mink coat or a white-washed wall, will end up being middle grey on your print if you have exposed according to that reading. Remember that; it is the basis of exposure control.
This calibration (light intensity registered = middle grey tone) works out well enough for many scenes because there is a rough average distribution of light and dark values present and they "average out". Think of a checker board with black and white squares. The intensity of the light reflected averages out to a middle grey, leaving the black squares much darker and the white squares much lighter than this middle value. Film exposed according to that middle value would yield black squares and white squares. Great. No problem here.
Often, however, this averaged reading will not work. Many subjects and scenes have a bias of values one way or the other; there may be an over-abundance of very dark or very light values -- a small figure on a field of snow, performers spotlit on a large dark stage, the mink coat, or the white-washed wall. Think of the checker board again. This time imagine that all the squares are white except for one black one. The average reflected light reading would be very much higher than it was in the first case when there was an equal distribution of black and white squares. The meter reading, indicating an exposure that would render the average value as middle grey, would be wrong -- an underexposure. All our white squares would end up middle grey on the negative. In fact, we would need to use the same exposure that we did in the case of the first checker board in order to reproduce black and white squares as black and white values. But, given the unequal distribution of values of the second case, how can we find the proper exposure? Using the Zone System. We can decide how much darker or lighter value we are actually reading is middle gray (Zone V) and adjust the exposure accordingly.
Any value (or Zone) on the scale is produced by twice the light or half the light of an adjacent value in the scale. Now this is very nice, because that is exactly equivalent to a change of one unit in f/stop or shutter speed. For example, an exposure of f/5.6 at 1/2 second may yield a tone in the scene an Zone V in the print ; cutting the exposure in half, f/8 at 1/2 second, will render that same tone as definitely darker, Zone IV. Cutting the exposure in half again, f/11 at 1/2 second, will produce a still darker grey, Zone III. Cutting it in half again f/16 at 1/2 second, will produce a very dark Zone II. Cutting it in half again will produce black.
Going the other way, doubling the exposure which yields a tone as Zone V will make that same tone appear lighter, Zone VI. Three more doublings of exposure value would finally yield white, Zone IX.
Here are three methods for determining exposure, based on the principle of the Zone System:
1. Read the light reflected off your own hand. If you are light-skinned, it is about Zone VI; therefore, increase the exposure by one f/stop or shutter speed unit (change f/8 To f/5.6, for example). Doing this will render you r hand, meter- calibrated to be Zone V, as one value lighter, Zone VI, so use the meter reading from the palm of your hand without increasing it.
2. Read the very darkest area in which you want detail, the very lightest area in which you want to keep detail, and set the f/stop midway between the two.. For example, if the dark area detail reads f/4 at 1 second, and the light area detail reads f/16 at 1 second, then the correct setting would be f/8 at 1 second.
3. Read darkest area that you want detail in and reduce exposure by two units of shutter speed or f/stop. This is effectively "placing" the metered area (calibrated to be Zone V) in Zone III. For instance, you might change f/8 at 1/60 second to f/8 at 1/250 second.
The "zone system" in photography is based on the fact that it is not only easy but practically necessary to vary exposures in units with a relationship of 1 to 2. In other words, when you change an exposure -- with shutter speeds, diaphragm openings, or calibrations on the light meter -- you always (if you make a change of one unit) either double the exposure of the previous setting or cut it in half. This is nice, because it WORKS easily -- not only arithmetically, but also photographically; exposure variations less than double (or half) produce results too slightly different to be readily noticeable, BUT greater variations are apparent enough to affect the quality of our work. The "zone system" continues this same 1 to 2 rhythm, and is based on the action of ordinary black and white film. Since most of us work with rolls of film and, therefore, have little or no opportunity to develop individual exposures individually (as is possible and easy with sheet film), this introduction deals only with the exposure possibilities of the zone system and its uses with normal development. For that reason I hope it will prove useful to anyone who normally develops normally (whether with rolls, film packs, or sheets) -- and even for making color slides developed by Kodak.
There are nine "zones" in the standard chart-- it just happens to come out nine -- no other reason; it seems useless to go beyond black at one end and white at the other. Zone V is in the middle, and it represents the grey of the Kodak "grey card", which is exactly half way between black (Zone I) and white (Zone IX). If you took a careful reading on the grey card with a good light meter, exposed black an white film accordingly, and developed and printed normally, the grey in the final print would be exactly the same grey as the grey care. But, if you did everything the same except that you cut the exposure in half, the final print would show the grey card (in the photograph) as definitely darker (Zone IV) . If you cut the exposure in half again (1/4 the original -- or "normal": -- exposure), the grey card in the photograph would come out as even darker (Zone III). Cutting it in half again (1/8 normal exposure) would produce a very dark grey (Zone II). And cutting it in half again (1/8 normal exposure) would produce a very dark grey ( Zone II). And cutting it in half again (1/16 normal exposure) would produce a solid black ( Zone I).
Going the other way, doubling the normal exposure would make the grey card in the photograph look definitely lighter (Zone VI) -- and so on till 16 times normal exposure would make it come out white ( Zone IX).
You don't get any detail in either Zone I or Zone IX; They are solid black or solid white. There is a little (very light) detail in Zone VIII, and a little (very dark) detail in Zone II. Zone III has quite a lot of detail, but it's quite dark; and Zone VII has quite a lot of detail, but it's quite light. And so on.
Since these variations are dependable, they are as useful as a ruler. Don't worry if all this doesn't mean much to you right at first, but think about it when you examine your negatives and prints (or slides), and soon it will start to mean something and become more and more useful. One way it can help a beginner -- even one who takes only color slides -- is just to compare two slides of the same subject taken at the same time, with no variation save that one slide has twice as much exposure as the other. This will merely illustrate just how much (or how little ) difference it makes when you double (or halve) an exposure. And having a good visual memory of that variation will be very useful to any photographer in taking the kinds of pictures he wants.
One occasion when the Zone System comes in handy is when you have great variations of light reading in your subject. This can happen either because of the varying tone of the subject itself or because of variations of light intensity. This problem can occur when you are making a copy photograph of a painting or drawing; you don't know where to point the meter, since the values of the painting may be constantly changing -- or in a drawing nothing may affect the meter except the white paper, the lightest value in the drawing. Taking the reading on the grey card usually solves this problem,. since most subjects include values both lighter and darker than the grey card(Zone V). But if all the tones in your subject are either darker then the grey card (a mink coat) or lighter (a drawing of light pencil lines and very light color tints on white paper), the grey card reading probably will be wrong. Knowing how much difference there is between zones will help here, for you will probably get better tones and detail in the dark mink coat if you expose it one or two zones MORE than the grey card indicates -- and truer and richer colors in the light drawing by exposing it one or two zones less than the grey card says. In both of these exceptional cases the grey cared reading (Zone V) would be wrong for the subject, because the subject includes few, if any, Zone V values.
In a three-dimensional scene or situation the grey card may be completely useless, because the light itself may have great variations within the picture. I was in such a situation in California once inside the old Mission at San Juan Bautista. There was a beautiful, old, wooden stair to the choir loft in a room lighted only by one window, and this window had to be in the picture. In such a situation it would be easy to overexpose the window so much that it would show only white (Zone I). There use to be a good, old, wise saying among photographers that went like this: Expose for the shadows, and develop for the highlights. The wisdom behind this is that if you don't expose enough to get shadow detail, you won't get any detail in the shadows, and, if you overdevelop the highlights (which are probably already overexposed simply because they're highlights), you won't get any detail in them either. The only trouble with this wise, old saying is that it doesn't tell you how much. The Zone System will tell you.
What I did in the case of the stair scene (Remember?) was to take on reading on the white window frame, and I decided that would be Zone VIII (very light but still with detail). Then I took another reading on the dark door and decided that couldn't be below Zone II (very dark but, still with detail). By starting at both ends and working toward the middle (Zone V), where the actual exposure had to be -- though there was nothing in the scene I could recognize as being Zone V in order to take a light reading from it -- I exposed the film at what I hoped would be an exposure that would accommodate both the light and dark extremes. The negative, developed normally, turned out to be very easy to print-- with detail in both the light, white window frame and the dark, shadowed door.
BUT I have not always been so lucky -- and you won't be either. Sometimes in churches - and many other situations -- the range of light between the darkest places where we want detail and the brightest highlights (often the light sources themselves being part of the picture) will be greater than any film can accommodate. In such cases you cannot start at both ends and work toward the middle; you must start at the dark end and expose enough to put the dark areas in Zone II (or whatever other zone you choose)-- and let the highlights be overexposed. There is no way to get shadow detail other than by exposing the film long enough to get it. If doing this overexposes the highlights, as it will do in many cases, the solution is not to sacrifice shadow detail but rather to under-develop the negative enough to prevent the overexposed highlights from becoming unprintably dense. But that involves the second part of the Zone System, and this part is only about exposing correctly for normal development (see page 1).
What I used to do before I knew about the Zone System was to follow the wise, old saying and take the reading on the dark door (because you have to "expose for the shadows"). What I didn't realize in those bad, old days was that this puts the dark door in Zone V, a normal grey, which it wasn't, and of course that upped all the other values in the picture, throwing all the light areas such as the window, etc. clear off the scale--somewhere lighter than white. As if this were not bad enough, there were no blacks or dark greys left in the picture, because I had put them in or near Zone V (medium grey) by "exposing for the shadows". Since I started using the Zone System-- even though even I don't understand it completely -- my negatives are a lot easier to print-- in fact some of them are even possible to print, and, since I am basically a lazy person, I am now much happier. Also, I get much more beautiful grey tones in my photos, and I'm happy about that too.
Harold Allen
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