I put ‘correctly’ in quotes because everyone has their taste. So what does ‘correctly’ mean here?
What it means here is the way to get the maximum information out of the scene. Put simply, if the shot is underexposed then some of the dark areas may not show detail. Or if overexposed then the highlights might be blown and not show detail.
The Zone System is a method of getting an optimal exposure of black and white photographs. It was created by Ansel Adams. a landscape photographer, and Fred Archer, a portrait photographer.
The method divides the tonal range of a scene into eleven zones from pure black to pure white. Notice that the range starts with Zone zero.
Zone 0: Pure black (no detail)
Zone 1: Near black (minimal detail)
Zone 2: Very dark shadow
Zone 3: Dark shadow with visible texture
Zone 4: Slightly darker shadow with good detail
Zone 5: Middle gray (18% gray), average light meter reading
Zone 6: Light gray (skin tone, sunlit grass)
Zone 7: Bright highlights (texture still visible)
Zone 8: Very bright highlights (minimal detail)
Zone 9: Near white (no detail)
Zone 10: Pure white (no detail)
To use it you measure light in your chosen part of the scene with your light meter. That may be a hand-held meter or the meter built into your camera. Whichever it is, all light meters are built to ‘assume’ that all scenes are Zone 5, middle grey. That is of course not true. A black cat in the snow for example.
And before we go any further you should know that while it is true the meters in cameras are based on middle grey, modern cameras are also computers. They look at the scene and measure it against a bank of similar scenes in their built-in database. If a camera stores 90,000 scenes then the chances are it has a black cat in the snow in there. So even assuming the light meter works on 18% grey Zone 5 and is wrong, it will correct itself if it recognises the scene.
And even if a camera does not have a built-in database of scenes, it will have metering that can cover most of the scene and then average out the brightness.
At the other end of evaluative metering, cameras now have AI or machine learning so they learn more scenes the more photographs the photographer takes.
In 2024 with built-in scene recognition and intelligent exposure adjustments we are a long way from Kansas.
So for the rest of this article I am talking about the zone system used with a hand-held light meter,
The Method
Put your camera on manual exposure. Point the light meter at the part of the scene you want to measure. The part you want to measure is the part in the scene that is important to you. Everything else in the scene will be measured by reference to that.
The meter will always give you an exposure (shutter speed and aperture) for Zone 5. Decide what Zone your chosen area should actually be in. Yes, that means you have to put your brain’s evaluative input into the calculation. Adjust the exposure. If you think the part of the scene you measured is Zone 3, then reduce exposure by two stops. In other words you are saying the following.
My starting point was to meter the brightness of the part of the scene I think is important. Now I want to expose darker than the meter is telling me because in my opinion the bit of the scene I want to measure is not mid grey, It is two stops darker than mid grey. So I reduce exposure by two stops.
That’s it. That’s the Zone system.
Meanwhile, with digital photography it is just a ‘flick of switch’ as it were to make a black and white version of a full colour image. Click on the image to see a large version.
By the way this is a crop of about one seventh of the full frame of a photo I took of this couple, from across the street with a 50mm lens on a Nikon D750.
