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Exposure
Camera photo zone systems photographic zone explained

Understanding Exposure & the Zone System

Knowing how your camera works is the key to getting good exposures. No matter how sophisticated your camera is, the exposure system works on the same principle, and that is to take a reading of the light and then average it. This is fine if the scene being exposed has a lot of average tones reflecting an average amount of light. Problems occur when you want to take a picture like the one at the top of this page. There are very few average tones in the image.

So what happens when you rely on the camera's exposure meter? Using the example below let's see what happens if we take the photograph without any compensation.

The camera has tried to average the tones in the photograph and the result is a badly UNDER-EXPOSED photograph.

So how do you get the right exposure? Let's say that you are taking the picture above and your camera says that the exposure should be 1/250th of a second at F11. If you took the picture at that setting your whites would turn out grey.

To get the whites to be white you need OVER-EXPOSE by around 2 stops. Many cameras have either a manual exposure setting or an exposure compensation feature. The common symbol for this is +/- . Using the camera's meter reading of 1/250 @ F11 as an example you need to OVER-EXPOSE so that your new exposure setting is 1/250th @ F5.6 OR 1/60th @ F11 (you can change either the aperture or shutter speed, it doesn't matter from an exposure point of view). So by opening the camera up 2 stops (letting more light in) you get white whites and bright, true colours. Your photograph would then hopefully turn out like the one below.

So what is a 'stop'?

A stop is simply a term to denote the halving or doubling of the exposure. For example, in the example above I said that you need to open up by 2 stops. Opening up one stop would mean that the exposure had doubled, your whites would now be twice as bright. Opening up two stops is a four-fold increase in the amount of light - a doubling of twice the original amount of light. You might think that twice as much light sounds like a lot. It isn't.

Let us use an example of an exposure of F8 @ 1/125th and we want to open up a stop. We can use either the lens aperture or the shutter to control the amount of light, so let us open the shutter by an additional stop, so the shutter speed is now 1/60th while the F-stop remains the same. If we then open up a further stop we are at 1/30th - four times as much light as the original setting of 1/125th. Think it through a little, it might take a minute but it is really simple.

Setting up your monitor

In the black square above you should be able to see a dark grey disk. If you can't, you may need to adjust your monitor's settings.

Either do this using built in monitor calibration software (like Apple's ColorSync software), or by turning the contrast up to the maximum (the symbol for contrast is a circle with split vertically in half, one side black the other white) and then turn the brightness up until you can see the circle in the square above (the symbol for brightness looks like the sun).


Another example

Because your camera is trying to average the meter reading to a middle grey, the exposure problems you have with whites as in the snow scene on the left are the same for blacks.

If I had taken the photograph at the top of the page without compensating by UNDER-EXPOSING by 2 stops it would have turned out like the small image above. Remember, you would UNDER-expose (let less light onto the film) because you want to make the black blacker. So, if your camera said 1/125 @ F8 you could go to 1/125 @ F16 OR 1/250 @ F11 OR 1/500 @ F8.

The Zone System

Understanding the Zone System isn't hard. In fact the basic concepts are really quite simple and easy to apply. The key points are:

  • A scene can be divided into 11 'Zones'.
  • Each zone is one stop apart.
  • Your camera's meter is calibrated for Zone V, or 18% grey.

Each numbered circle on the photograph above shows the zone of that part of the photograph. Compare the zones with the list on the right.

Referring to the snow scene above you can now see that you should have snow around Zone VII. So, to achieve this you must OVER-EXPOSE by 2 stops. And on the black wood panels with the Chinese writing you should have the black on Zone III - UNDER-exposing by 2 stops.

Which Zones Are What?

Zone 0 Total black
Zone I Black without any texture
Zone II Black with slight suggestion of tonality
Zone III Darkest areas that still retail some visible detail
Zone IV Average shadows in landscapes or portraits
Zone V Middle Grey - 18% grey card
Zone VI Average Caucasian skin
Zone VII Lightest areas in any scene that still retain some visible detail
Zone VIII White areas with slightly visible textures
Zone IX Glaring white surfaces. Highlights without any texture
Zone X A light source

By convention, Zones use Roman numerals.



Spot-Metering

Not all cameras have a spot-meter, but it is a useful feature, and a powerful tool especially if used in conjunction with the Zone System. The simplest way to use a spot-meter is to find a tone on Zone V and meter off it.

If there are no Zone Vs in your image, spot-meter off another area and 'move' your exposure. Again, using the example of the black panel at the top, spot-meter off the black wood and then change your exposure by 2 stops to UNDER-expose it.

I spot-metered off the woman’s cheek to ensure that the dark background and the candles didn't throw my metering. I then adjusted the exposure compensation by -1 stop.

Spot-meter off the grass where possible ensuring that the same amount of light is on the grass as the subject. Grass is usually Zone V.