What does a properly exposed photograph look like? By properly exposed, we mean that the photo you get back looks the way you imagined that it would. If you want a blue sky, the sky comes out the right shade of blue. If your goal was a silhouette but your photo shows all the details of your subject, you overexposed the film, even if another person thinks that the picture is perfect. So how do you decide what you want and how do you get your vision onto the film?
Camera meters are relatively simple devices. They don’t think, they simply react to the situation in a predictable way. Our job is to learn what the meter will do and compensate to get the results we want. Some cameras have more metering zones than others, but each zone works in the same basic way.
The Light Meter
Light meters are found inside your camera. Older meters are usually “center-weighted”, meaning they read the amount of light within the center of the frame. Newer cameras usually offer more complex meters, allowing them to read the amount of light from many places within the frame. There is usually a box or circle in the viewfinder that designates the metering area. As the light changes within your metering area, your camera will give you some kind of indication of that change.
Meters are very simple tools. They cannot see color. Meters only read tonality, the darkness or lightness of an image. The meter looks at the light in the viewfinder and recommends an exposure by comparing the light pattern and quality with some kind of reference. Meters read the amount of light in and average it. The meter looks at the brightest spots and the darkest spots and says, “Let’s be safe and put it in the middle.
This is fine, if you are after “average” toned images. But if you are photographing dark black rocks, instead of getting black rocks, you would get gray rocks, as the meter would average the light to capture gray rocks. If you were after white snow, your film would come back as gray. The meter can’t think “Oh, this is snow. I need to make it white.” It can only “average”.
Understanding how the meter works is very important when photographing extreme or unusual lighting conditions. Let’s explore it just a bit further.
There are four variables which can affect your camera’s meter: the aperture on the lens, the shutter speed, the quantity of light available at the time you take your picture, and the brightness or tonality of your subject. Your camera already knows the aperture and shutter speed because you either set these manually, or you let the camera choose them. That leaves the quantity of light and the tonality of your subject – and your camera meter has no way to tell the difference between the two.
If the sun goes behind a cloud, the quantity of light decreases, and your meter will register that change. In the same way, point your camera at a light colored rock, then point it at a dark rock, and the meter will tell you that the exposure has changed, even though the light has not.
Camera designers had to make a choice. What they chose was to calibrate the meter to accurately expose “middle-toned” subjects, those subjects neither light nor dark, but somewhere in between. The reference point they chose was 18 percent, roughly three stops brighter than black and three stops darker than white. A subject that reflects 18 percent of the light that strikes it is called a middle-toned subject.
Probably the hardest technical problem photographers have to overcome is learning how to use their meter to make a properly exposed photograph. Since your camera’s meter is calibrated to properly expose middle-toned subjects, it stands to reason that any subject that is not middle-toned will not be properly exposed. Here is the catch: Your meter does not tell you how to make a properly exposed photograph. It tells you how to make the thing you are metering come out middle-toned. If your subject is middle-toned in real life, then your exposure will be perfect. But unless we override our camera’s meter, dark subjects and light subjects will also come out middle-toned. And that’s not right.
Going Against the Meter
So how do we fix the problem? If we meter a light subject, like a snow-covered field, we know what the meter is going to do. It’s going to make the snow look middle-toned, or gray. We don’t want gray snow, so we have to manually compensate by adding back in the light that the meter has told the camera to remove. We add extra light to the exposure of light-colored subjects to make them appear normal in the photograph. And we do this by either opening the aperture or by slowing the shutter speed from the value that our meter tells us.
In the same way, suppose we are photographing a dark subject like wet tree bark or a dark rock. Our meter is going to try to make the bark look middle-toned. It tries to make everything we point it at look middle-toned. So we have to manually compensate by taking away the extra light that the meter has told the camera to add. We remove light (or add darkness) from the exposure of dark-colored subjects to make them appear normal in the photograph. And we do this by either closing down the aperture or by increasing the shutter speed from the value that our meter tells us.
Let’s go over that again. Meter your subject. Compensate from what your meter tells you by adding more light for light-colored subjects or by subtracting light for dark-colored subjects. Take the picture. A handy phrase to help us remember this is: Add light to light, add dark to dark.
Add light to light, dark to dark
How much light should we add or take away? Slide film has a latitude or a range of tones that it can record of about 5 to 6 stops from overblown white to blocked up black. The range of tones might look like this:
|Meter adjustment||Subject Tone||Tonal Shift|
|+2 stops||Very light subject|
|+1 stop||Light subject|
|0 stops||Middle-toned subject|
|-1 stop||Dark subject|
|-2 stops||Very Dark subject|
To be honest, the number of natural subjects that require the addition of two stops is rare; white sand and snow on a cloudy day are the only ones that comes to mind, and I can’t think of any that require a minus two stop correction. I would expose even a black bear at minus one stop from my meter reading because I want to make sure I can see the detail in its fur.
When working with extreme light conditions, or specialized light, your camera can be fooled into seeing something different from the image you wish to capture. As stated, the meter reads the brightest spots of light and the darkest spots of light and decides what is the in-between exposure. It averages everything it sees. To get a really dark silhouette, we need to underexpose the image since the meter will try to produce a medium tone.
Use the phrase “Add light to light, add dark to dark”. When you want something to be as dark as the eye sees it, you fool your camera meter and add “dark” to the image. You can add dark by increasing the shutter speed or by closing down the aperture.
White colors influence the meter reading, fooling it into thinking that there is too much light. The white snow and ice on this bright white glacier is just too much light, so the meter shuts down to even out the light, turning the glacier gray. By adding light, we add back what is taken away by the meter to correct the light to make the glacier white, the color it should be.
The meter read this bright white glacier as too bright and “grayed” it to average.
By adding “light to light” by slowing the shutter speed to let more light in, the “white” was achieved.
Another example is the trick bright white objects like snow and fog can play with the meter. Unless we compensate, snow will be exposed as dark and almost dirty because the meter shifts the exposure to middle-toned. Using the “add light to light” theory, by overexposing or adding light to the image, the snow becomes whiter. The eye saw white snow. Not dirty snow. Using the “add light to light” idea, it becomes easy to adjust for light- or dark-toned subjects.
- Metering for Average
- Find a subject that you think is middle toned. Make a series of five exposures from two stops underexposed to two stops overexposed.
- Light to Light
- Find a light subject and photograph it at the meter reading, and at one and two stops over.
- Dark to Dark
- Find a dark subject and photograph it at the meter reading, and at one and two stops under.
Metering by Proxy
We said the camera’s meter is calibrated to make a correct exposure of a middle-toned subject. If our subject is middle-toned, we can simply meter it and take the picture. If our subject is not middle-toned, we adjust our exposure to compensate using the “light to light, dark to dark” theory. But this means we have to make a mental estimate of how far the subject is from middle-toned. Is it a half stop or a full stop brighter than neutral?
There’s another option. If we could find a middle-toned object in the same light as our subject, we could simply meter this object, recompose, and photograph our subject without directly metering it. This is possible because when we meter, we’re measuring the amount of light. If two objects are in the same light, and if the exposure is correct for one of them, it should be correct for the other one, also. The key is that the two objects must be in the same light. If you meter an object in the shade while the other is in full sun, your exposure will be incorrect.
Some photographers carry a middle-toned subject with them wherever they go for this purpose. This is called a “gray card”, and it reflects exactly 18% of the light that strikes it. Meter the gray card, set the exposure, and any other object in the same light as the gray card will be properly exposed.
What if you don’t have a gray card? The one object that every photographer has is the palm of his or her hand, but your hand isn’t middle-toned. Whether your skin is light or dark, white, black, pink, or some other color, the palm of your hand is about one stop brighter than middle-toned.
To use your hand to make a correct exposure, compose and focus on your subject. Then, if you have autofocus, turn it off. Without focusing, fill the frame with the palm of your hand, taking care to ensure it is in the same light as your subject. Make a meter reading and open up one stop by opening the aperture or slowing the shutter speed by one stop from what the meter told you. Point the camera at your subject to recompose if necessary, and take the picture. It’s simple, and it works for everyone on the planet.
Aperture and Shutter: How do they relate?
A camera in its simplest form is just a light-tight box that holds the film in place with an opening in front to let the light in. A lens is placed in front of the opening to focus the light on the film. A device called the shutter opens and closes to control the amount of time the light is allowed to strike the film. The aperture inside the lens changes size and controls how much light is allowed to pass through.
Examples of aperture openings on lenses.
Lens open wide at f 1.4
Lens open medium at f 8
Lens open smallest at f 22
The shutter is like a curtain. When it opens, light passes through. It can be opened and closed very slowly to allow a lot of light to pass, or very quickly to allow a small amount through. Its speed is variable and is controlled by the photographer. Most cameras have a range of shutter speeds from 1 second to 1/1000 of a second. The fastest camera on the market has a top shutter speed of 1/12000 of a second (Minolta 9xi). At the other extreme, times of many seconds or hours are possible for low light or night photography.
The standard series of shutter speeds is 1 sec, ½ sec, 1/4 sec, 1/8 sec, 1/15 sec, 1/30 sec, 1/60 sec, 1/125 sec, 1/250 sec, 1/500 sec, 1/1000 sec. Each shutter speed is twice as fast as the one before it. That means that each successive shutter speed allows only half as much light to pass through before the shutter closes.
The aperture is like the pupil in the eye. It opens wider to allow more light to pass and closes to restrict the amount of light through. It also controls the depth of field. On most older cameras, the aperture was adjusted by turning a ring on the outside of the lens. Many newer cameras have dials or adjustments on the camera body itself.
The size of the aperture is denoted by the f -stop selected. The standard series of numbers is 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32. This series seems odd at first, but there is a mathematical relationship between each f -stop and the next–each number is 1.4 times larger than the one before it. The diameter of each opening is 1.4 times smaller than the one before it, and that means that it lets in half as much light. To repeat, each aperture lets in twice as much or half as much light as the one next to it. And the bigger the f -stop number, the smaller the opening.
The Water In The Bucket Theory
Examples of the under and over exposure elements of photographic exposure.
Overexposed – too much light
Proper exposure – just enough light
Underexposed – not enough light
The aperture and the shutter speed work together to control the amount of light. A good way to think about them is with the analogy of a bucket of water and a faucet. If you want to fill the bucket with water, you can do it with a lot of water for a short amount of time, or with just a trickle for a long time. The amount of water it takes to fill the bucket is the correct exposure, the correct amount of light for a properly exposed picture. The handle on the faucet is the aperture which controls how fast the water fills the bucket. And the time the faucet is on represents the amount of time that the shutter will let the light in. Obviously, if you want to fill the bucket faster, you have to get more water through the faucet and that is limited by the physical size of the faucet. Another option to filling the bucket faster is to get a smaller bucket, that is, to use a faster film which requires less light.
In a real situation, you are faced with certain lighting conditions over which you have little control. You have to choose a lens, aperture, shutter speed, and film that matches the conditions. Assuming you only have one lens and one type of film with you, let’s look at the aperture and shutter speed.
The first thing we usually do is decide which aperture to use. We’ll talk about depth of field and aperture later, but let’s say that f 8 is the best choice. Take a meter reading and the camera will say what shutter speed it should use. Let’s assume that the meter says 1/125th of a second will give a proper exposure. Does this mean that the combination of f 8 aperture and 1/125 shutter speed is the only choice? No.
Remember that each aperture and each shutter speed are related to the next one by twice as much or half as much light. So f 11 is half as much light as f 8 (the bigger the f -stop number, the smaller the opening). If we set the lens to an aperture of f 11, we have reduced the size of the lens opening so that only half as much light gets through. To compensate, we have to add more light for a proper exposure, so we do that by slowing the shutter speed one setting from 1/125 to 1/60. We also could have set the aperture to f 4 and the shutter speed to 1/500, for example; there are many correct combinations.
Since there are so many combinations which give a “correct” exposure, how do you decide which one is best for you? This is a creative decision, and one which can give your pictures an entirely different feel.
Examples of shutter speeds controlling the speed of a moving subject. A friend rides by on a bicycle and you can see the difference in the speed of movement based upon the shutter speed.
250 th second at f 4
60 th second at f 8
15 th second at f 16
1/4 second at f 32
The shutter speed you choose for a moving subject has a direct impact on the feeling of speed that shows in your picture. A fast shutter speed will stop the motion, freezing action. A slow shutter speed will allow any movement to blur, while those parts of your picture which are not moving will be sharp. A general rule of thumb is that moving subjects require fast shutter speeds and the faster they move, the faster the shutter speed required. An animal which is perfectly still may be photographed as slow as 1/15 to 1/30 with a reasonable chance of getting a sharp picture, if your technique is perfect and you take several shots for insurance. But a moving animal will usually require 1/250 or faster.
The aperture you choose is an equally important part of the decision, because it directly affects the depth of field. Depth of field is the range of apparent sharpness from front to back in your photograph. Objects within the depth of field appear sharp, and those outside of it are out of focus. The larger the f -stop, the smaller the aperture, and the larger the depth of field. To repeat, the larger the f -stop number, the larger the depth of field. The smaller the f -stop, the smaller the depth of field. What this means is that if you want as much as possible to be in focus, stop down as far as your lens will allow, usually f 22 or more.
In most cases, a large depth of field is wanted for scenic photographs. We want to see the detail in the flowers in the foreground and the mountains in back. f 22 is a good choice. At other times, an out of focus background eliminates distracting elements so that our attention is on the subject, as in a closeup of a single wildflower. I might shoot this at f 4 or maybe f/5.6. In some cases, it just doesn’t matter which aperture to use, so I pick one in the middle like f 8 or f 11. Look in the Popular Photography lens tests and you will see that almost all lenses are at their best around f 8 and f 11, exhibiting greater sharpness and less distortion.
The amount of light allowed into the camera, exposing the film, controls much of the artistic quality of the results. A shallow depth of field caused by a wide aperture blurs the foreground and background of a subject. A moving object is controlled by the amount of light coming through in a combination of shutter and aperture controls which slows the shutter speed down to trace the movement of the subject across the screen, such as with the waterfall below.
To add a sense of distance to this landscape of an old barn, we chose a small depth of field (large aperture) to blur the flowers in the foreground.
A slow shutter speed creates a blurred motion effect of this waterfall.
Like all things in life, there are tradeoffs between aperture and shutter speed. We have to have a certain quantity of light to make a proper exposure; remember the bucket of water? If we close the lens down to get more depth of field, we may not have enough light to stop the motion of our subject. Open the lens for a fast shutter speed to stop the motion, and the depth of field may suffer. Or we make knowing decisions by understanding how our equipment works, and therefore we know a larger aperture will give us a shallow depth of field and a slow shutter speed will blur our subject. These creative possibilities allow us to play with exposure to create the effect we want. So we have to strike a balance and get as close as we can to the vision we have in our mind.
The following exercises are the kind of problems you are likely to run into in the field. Working these will help you deal with any exposure situation. The answers will be found below the Exercises.
1)How many stops are between f2.8 and f4? f4 and f5.6? f5.6 and f11? f2.8 and f16? From halfway between f4 and f5.6 to halfway between f8 and f11?
2)How many stops are between 1 second and 1/2 second? 1/2 and 1/4? 1/125 and 1/500? 1 second and 1/1000?
3)Suppose your meter tells you that proper exposure is f5.6 at 1/125. What is an equivalent exposure at f4? f16? What aperture would give you 1/30 of a second? 1/8 of a second?
4) If your meter tells you that f5.6 at 1/125 is correct and you instead shoot at f4 at 1/125, have you added more or less light? How many stops? Is f11 at 1/60 more or less light? How many stops?
5) Your meter tells you that f5.6 at 1/125 is correct. If you keep your shutter speed at 1/125, what aperture would add 2 stops of light? If you shoot at f5.6, what shutter speed would make your photo 2 stops darker?
Add Dark to Dark, Add Light to Light
Consider the following pictures and estimate how much “dark” or “light” you would add to the average meter reading shown to create the “right” exposure.
Green grass with burnt trees in background, Alaska; Male Elephant Seal (gray colored), California; Autumn colored leaf on burnt log; Yellow daffodils
- Depth of Field
- Select a fence or a row of trees. Focus on the fence about midway in front of you. Take three shots, at your largest aperture, f8, and the smallest. Adjust your shutter speed for a correct exposure in each case. Notice how the depth of field changes.
- Shutter Speeds
- Find a moving subject like a car on the road, jogger or walker. Shoot at the fastest shutter speed possible (this will be at your largest aperture). Make another exposure at f8, and a third at the longest shutter speed possible (at your smallest aperture).
1) f2.8 to f4 is 1 stop. f4 to f5.6 is 1 stop. f5.6 to f11 is 2 stops. f2.8 to f16 is 5 stops. f4/5.6 to f8/11 is 2 stops.
2) 1 sec to 1/2 sec is 1 stop. 1/2 sec to 1/4 sec is 1 stop. 1/125 to 1/500 is 2 stops. 1 sec to 1/1000 is 10 stops.
3) f4 at 1/250. f16 at 1/15. f11 at 1/30. f22 at 1/8.
4) Added one stop. One stop less.
5) f2.8. 1/500.
Add Dark to Dark
1) Grass is neutral – no change
2) Elephant seal is neutral – no change
3) Burnt log is black – add dark or meter for red-gold leaf and add light
4) Daffodils are yellow (light) – add light