Metering without a screen: Sunny 16, grey cards and the Zone System

Many film cameras have no meter, and plenty of old ones have meters that should be checked against a known reference before you trust them. You can still shoot them all day, because daylight is predictable and the makers print the numbers on the datasheet. From there it is a short step to a hand meter, and from the meter to the Zone System, which is just a way of talking precisely about what the meter is telling you.

Sunny 16

The rule: in bright sun, set the aperture to f/16 and the shutter to one over the film speed. Kodak's current Tri-X sheet is the rule written out. For Tri-X 400 in bright or hazy sun with distinct shadows: 1/500 at f/16. On light sand or snow: f/22. In weak, hazy sun with soft shadows: f/11 ¹. The table is for average front-lit subjects from two hours after sunrise to two hours before sunset ¹; Kodak's Portra 400 sheet carries the same hours ². Backlit close-ups get two more stops, f/8 at 1/500 for Tri-X 400 ¹. The further down the table you go, cloudy bright, open shade, the more a meter earns its keep, but on a clear day within the table's conditions the rule gives a reliable starting exposure, and it is quick.

What a meter measures

A reflected-light meter, the kind in the camera, assumes the scene it sees averages to middle grey and tells you the exposure that will render it so. Point it at snow and the snow comes out grey; point it at a black cat and so does the cat. Kodak's curve diagram for Vision3 500T gives the spacing on that film: an 18 per cent grey card is "normal exposure", a white card sits 2⅓ stops above it, and a 3 per cent black card 2⅔ stops below ³. So if you fill the meter with a white wall and want it white, opening up about two stops is the starting point; the exact amount depends on the tone you want and on your meter. An incident meter, with the white dome, measures the light falling on the subject instead and sidesteps the problem; it is why portrait and studio photographers carry one.

A grey card does the same job for a reflected meter: hold it in the subject's light, meter it, and set that. It is the cheapest piece of darkroom equipment that improves negatives.

The Zone System in one page

Ansel Adams, in The Negative, divides the tonal scale into eleven zones one stop apart, Zone 0 to Zone X: 0 the deepest black the paper can make, V the middle grey a meter reads for, X paper white ⁵. The useful ones to memorise are Zone III, dark with full texture, and Zone VII, light with full texture. The method has two halves. First, placement: with a spot meter, or a reflected meter filled entirely by the area, meter the shadow you care about and set the exposure so it falls on Zone III, two stops less than the meter says. Second, development: meter the important highlight, see which zone it falls on, decide which zone you want it printed as, and if it lands higher than that, develop less (Adams' N minus); if lower, develop more (N plus) ⁵. How much less or more is found by testing your own film and developer, which is most of Adams' book. Hence the saying you will hear in every darkroom: expose for the shadows, develop for the highlights. Exposure sets the shadows because nothing in the tank can add detail that the film never received; development sets the highlights because the dense parts of the negative grow fastest with time.

With roll film

Adams worked with sheet film, one negative, one development. On a roll you cannot give frame 7 N plus one and frame 8 N minus one. The practical answers are to shoot a roll for one kind of light, to lean on the film's latitude for the rest, and to use the developer time to set the roll's overall contrast. Kodak's advice for D-76 is the roll-film version of the Zone System: if your negatives are consistently too low in contrast, increase development 10 to 15 per cent; if too contrasty, decrease it by the same ⁴. Ilford adds a conditional case: long exposures can raise contrast because the shadows fail more than the highlights, and if that happens, reducing development may be required, depending on the range of light in the scene ⁶.

Try this on one roll

Find a scene with a deep shadow you want to keep and a bright highlight you want to hold. Meter the shadow, close down two stops, and make the exposure. Meter the highlight and count the stops between the two readings. Five stops means the highlight lands on Zone VIII, light with a little texture; decide whether that is what you want. If the developed negatives come out consistently too contrasty, Kodak's 10 to 15 per cent cut is the roll-film adjustment ⁴, a trial you judge on the next roll rather than a calibrated N minus, made in the tank with the usual gloves, eye protection and ventilation. Then print or scan the frame and look at the shadow and the highlight you chose. That is the whole system, and after a few rolls you will do it in your head.