tonal values – The Lens Lounge

If you’ve never heard of the zone system, or you’ve heard that the zone system is no longer needed, because our cameras have in-built light meters, you’re missing a great exposure trick! The zone system was developed by a famous landscape photographer called Ansel Adams and a portrait photographer named Fred Archer in 1939-1940. It’s a way of looking at the world in black and white from your camera’s point of view. We’ll have a look at why the zone system is so helpful to know in a moment, but first, let’s look at how your camera's exposure meter works. Did you know your camera's exposure meter thinks in black and white? When it comes to exposure, color doesn’t matter to your camera, because it measures exposure in various tones from black to white. However, its favorite tone is neither black nor white, it’s medium gray, also called 18% gray. Your camera wants to make everything medium gray. Use spot metering with the zone system When using the zone system to help with accurate exposures, switch your camera's metering mode to spot metering. This is because we want to meter only a small part of the image, not the whole scene, or even the middle of the scene. We want to measure the smallest area possible, which is spot metering Further reading: Metering modes and how exposure metering works When to use spot metering? How your camera measures light This is really important to remember, because this is the basis of your camera’s exposure metering system. Cameras measure reflected light when metering exposure. Reflected light is exactly that - it’s the light bouncing off the object you’re metering. White objects reflect more light than medium gray objects and black objects reflect very little light, if at all. So, if your camera is metering the light off of a white object, it’s going to see a lot more light than when metering off of a black object. That's going to affect the exposure reading. I’ll put it another way… Meet our cat models Sooty, Smokey and Snowy. They’re near each other in the same patch of light. We’re going to use spot metering to meter the exposure and we’ll position the point on the lightest part of their fur. Sooty Black cat, Sooty, does not reflect light. Your camera’s exposure meter thinks that Sooty is too dark, because there’s very little light coming off him. The camera wants to set a slower shutter speed or wider aperture to lighten him up. But this will overexpose Sooty and make him medium gray, like Smokey. Smokey Medium gray cat, Smokey, reflects some light. Your camera’s exposure meter is happy with how much light he is reflecting and sets a shutter speed or aperture to expose him correctly. Snowy White cat, Snowy, reflects lots of light. Your camera’s exposure meter thinks that snowy is very bright so wants to darken him down. The camera sets either a faster shutter speed or a narrower aperture. But this will underexpose Snowy and make him medium gray, like Smokey. Your camera can record Smokey accurately without your assistance, because he is the tone your camera thinks everything should be. For Sooty and Snowy you need to help out by adjusting the exposure. Use exposure compensation if you’re photographing in: Program mode Aperture priority mode Shutter priority mode If you’re using manual mode, just increase or decrease the exposure by the appropriate amount. Great! So now you know how to fix this exposure problem and ensure that all your cats are correctly exposed. Further reading: How and when to use exposure compensation – controlling exposure part 3 But by how much do you need to adjust the exposure? It's all fine and well knowing that you have to help your camera out a bit when it comes to achieving the correct exposure for tones above and below medium gray. If you're just guessing at the exposure adjustment you need to dial in, that's not going to guarantee you an accurate exposure. This is exactly why the zone system is still hugely relevant today! Even with our fancy digital cameras. So let’s have a look at the zone system It's a lot simpler than it sounds. The zone system is a tonal scale moving from pure black to pure white to cover the full tonal range. There are 10 zones and each zone on the scale represents a 1 stop difference in exposure. In other words, with each step along the scale you need to adjust either your.. Shutter speed, Aperture or ISO ...by one stop. Further reading: What are stops in photography exposure? Medium gray, which your camera thinks is the correct exposure, on the zone scale is shown as V (5). You can see on the right of the table the changes you would need to make to the exposure for each zone for it to be accurately recorded. The zone system and color photography But you don’t see the world in black and white, so trying to figure out what color equates to what tone of gray is not easy. So here’s the zone system in color. This chart is also on the cheatsheet and is a really handy reference to keep in your camera bag until you know the zone system well enough not to have to refer to it. Are you seeing where this is going? If you have an idea of how your camera meters color, you’ll know how much to adjust your exposure. USEFUL TIP: If you want to meter off something that’s medium gray and you don’t have a gray card or Smokey, with you, point your camera at: The nearest healthy green grass in the scene The north sky (with no clouds) Weathered wood Why? Check out V on the zone system - it's medium gray and that's where they are on the zone system! Ta da. Remember to use spot metering for this. You don’t want to meter everything - just a small patch of medium gray. In these examples you can see how different colors can look the same in black and white, because they have the same tonal value. If, for example, the green was a pastel green, it would be much lighter than the others in the black and white photo. The zone system for portraiture In this regard using the zone system is fairly easy, because when we photograph people, we meter for their skin. The most important part of the photo is the person, so they must be correctly exposed. The difficulty is that skin tones vary so much, so we can’t just give a one size fits all answer. Learn to judge skin tones and use this table as a rough guide. Exposure metering for portraits When metering a person’s skin, use spot metering and take your exposure reading off of the brightest part of their skin. This is usually the cheek closest to the light. As your exposure meter will want to make everything Zone V (medium gray), all you then need to do is adjust the exposure by however much you think is required for their skin tone. Just refer to the zone system chart for skin tones. Did you sign up for the cheatsheet? Here it is again. Remember each zone represents 1 stop of exposure. So, for example, average white skin would require +1 stop of exposure compensation. If you want to be certain, you can double check your readings by spot metering their skin and then spot metering a gray card. The difference between the two should match the table. The zone system measured tonal value from low (white) to high (black). Pastel colours have a low tonal value in a black and white image, which you can see with the boys' shorts in particular when compared with the darker blue of the sky, which has a higher tonal value. How the zone system helps to plan for black and white photography If you’re planning on a black and white shoot, think about what colors to include. Did you notice that yellow is the same tone as average white skin? Yellow clothing on someone with average or light white skin in a black and white photo is going to look very washed out as there’ll be very little tonal contrast. On someone with dark skin, it will contrast beautifully. Further reading: Black and white photography tips for beginners Editing black and white photos for impact Using the zone system, you'll see that average white skin is the same tone as light stone. Both are VI on the zone scale. In this photo the boulders behind the model are granite. Recap of the zone system in photography Before we wrap up, let’s go over the key points of using the zone system: The zone system was developed for black and white photography, but is relevant to color photography too. Different colors can have the same tonal value (blue, green, red). Skin tones vary, so have different tonal values. Use spot metering to meter your exposure when using the zone system. Medium gray, for spot metering your exposure, can be found in healthy grass, a clear north sky, weathered wood. Once you’ve taken an exposure reading, adjust your exposure according to the tonal values of the zone scale. Adjust exposure using exposure compensation if in program mode, aperture priority mode or shutter priority mode. In manual mode, simply adjust your shutter speed or aperture according to your requirements. Leave a comment If you have any questions about the zone system and exposure metering, let us know in the comments. Also, we love good news, so if our zone system tips have helped you to understand how to understand exposure metering, share that too. Will this photography tutorial help you to understand the zone system? Share the learning...