Getting in the Zone
The next step from the spot metering methodology covered in Your Camera May Be Lying To You is to translate the rather abstract exposure values into a logical and easy to apply exposure system.
Luckily, a little known photographer called Ansel Adams helped to develop just such a system with Fred Archer in 1940 – now known as the Zone System.
The basics are easy enough – the zone system is a set of shades from black through to white – 11 grades are used to divide up the shades as below.
So pure pure black is zone 0 and pure pure white is zone 10.
Zone 5 represents the midtone in the scene – this is the 18% grey tone that a lightmeter is looking for. Anything one stop darker will be Zone 4, two stops darker, Zone 3, and so on. Each shade is a stop from it’s neighbor.
Anything one stop lighter than the midtone will be Zone 6, two stops lighter, Zone 7, etc.
Most digital cameras can show detail in Zones 3 through 7, but not beyond that. (Without post processing)
So Zone 8 and above may be clipped, and Zone 2 and below are dark dark black or blocked black.
A light color will lose saturation above Zone 6, and a dark color goes muddy below Zone 4.
So how does this impact our image from the exposure testing?
We’ll start by selecting the key highlight—the brightest significant part of the scene that needs to have detail and texture. This would be the sunlit pillar in this shot.
Then we decide what zone that highlight should be. There are really only two choices. Zone 5 isn’t a highlight, it’s a midtone, while Zone 8 is potentially clipped.
So that leaves Zone 6 or Zone 7.
Use Zone 7 for objects that are light, such as sand or very light rock.
Next we spot-meter the highlight we’ve chosen – the pillar.
we get 1/1000 f/8 on our meter – which is of course assuming the target is a midtone 18% grey.
To make that area a Zone 7, we increase the exposure by two stops. In other words, if the meter indicates 1⁄1000 sec. at ƒ/8, we lower the shutter speed to 1⁄250 sec. to make that highlight Zone 7. (2 Stops)
We have our exposure for the scene – 1/250 at f/8 ISO200
We can go around the scene metering the same points as before and we can see how the various brightnes levels measured will translate into Zones.
The dark area in the porch is zone 3 – it’s 2 stops darker than our mid tone but will still show detail.
The grass is zone 5, it’s the same brightness as our mid tone. As mentioned earlier, we could have used the grass as a good analog for an 18% grey card, and used this to establish our mid-tone exposure setting.
None of the zones measured are outside of the range of the camera to register them – I’ve shown how the zones map to an exposure meter in the middle top of the image, and also how they map to a camera histogram top right.
We’ve successfully mapped our exposures to the Adams Zone System, and can use this to interpret a scene and judge how it will translate into a color or B&W image. We can judge the dynamic range, and make decisions about what in the scene should be a highlight, a dark area, pure white, pure black, or a mid tone.
Good B&W post processing software like NIK Silver FX will allow you to view the image in a neutral B&W conversion, and go through the zones (bottom right under the histogram) highlighting the areas for each zone on the image using a hatched overlay pattern.
Here, I have Zone 7 selected in the histogram window, and the image has a hatched overlay showing the stonework and some of the sky as being in zone 7.
As mentioned in the previous write-up, there’s far more to the Zone System, and a read of Ansel Adams The Negative is recommended.
It’s an old book – but it’s just as relevant today with DSLRs and Mirror-less Compacts, as it was when it was written.
When you’ve got this down, you’ll be able to do the whole thing without even needing a meter – well, that’s the theory any way…