Wednesday, February 25, 2009


What is Exposure?

At its simplest, exposure occurs when the film or digital camera's sensor is exposed to light. When a photograph is taken, light reflected from the subject and its surroundings is transmitted by the lens through the open shutter to the film or sensor for a set length of time. The film /sensor is then said to have been exposed.

The term "exposure," however, also refers to control by the photographer of the final appearance of his or her pictures when the images are being taken. A photographer who understands and applies the concept of exposure will unquestionably produce far more predictable images than the camera user who simply points and shoots.

When is exposure compensation useful?

  • If at first, you take an image and it looks to be too dark or too light when viewing it in your LCD screen. For example if it is early morning or late evening, you might want the photograph to appear lighter (or darker) than it actually is.
  • If you are taking a photograph of an object that is in actual fact too dark, and you want to lighten it. For example if you were taking an image of the underside of a car near the tyre. Bad example I know :) Or lets say you want to photograph a black bird and need to see the actual eye in your image. In this case you could slightly over expose the image to bring out the patterns and shapes.
  • In contrast, snow images can appear too over exposed. In these situations it's recommended to underexpose the image until you see a nice balance between the sky and the snow.
  • Exposure compensation is also useful for those people that photograph objects in a light tent. A light tent is a square box that has numerous colored backgrounds so photographers can capture products and objects with one background color. For example, if a white background is used and you don't change the exposure compensation, the background may appear off white.
How do I control it?

Typically, a light meter is used to determine the amount of light striking your subject and to provide shutter speed and aperture settings for proper exposure for that amount of light. Setting shutter speed and aperture correctly allows you to take properly exposed photographs. With a manual camera, the photographer adjusts shutter speed and aperture settings until the camera’s meter indicates proper exposure. Automatic-exposure cameras don’t require the photographer to make any adjustments, however there are numerous occasions when the photographer will want to over-ride a camera’s automatic settings to improve a picture.


Let us suppose that you are photographing a parade and your light meter indicates proper exposure using a shutter speed of 1/125 sec and an aperture of ƒ11. But, you want to use a faster shutter speed to freeze the action of those marching past, and decide that 1/250 sec would be more appropriate.

Changing from one shutter speed to another that is twice as fast (for instance from 1/125 sec to 1/250 sec) allows half as much light to strike the film, and therefore your picture will be underexposed. But, if you open up the aperture by one stop (i.e. from ƒ11 to ƒ8), it will allow twice as much light to come in, and you will have proper exposure again. The faster shutter speed reduced the light striking the film by 50%, but changing to a wider aperture compensated for this reduction by doubling the amount of light, thereby preserving proper exposure.

In this example, both 1/125 sec at ƒ11 and 1/250 sec at ƒ8 will give proper exposure, but the exposure with the faster shutter speed has more action-stopping ability.

What if a really-fast shutter speed had been chosen, like 1/500 sec? Well, that is two stops faster than 1/125 sec, and therefore the aperture would need to be opened wider by two stops, from ƒ11 to ƒ5.6. As you can see, there are many combinations that will provide you with proper exposure for the same scene. These are called "equivalent exposures." See our section entitled Shutter speed/aperture combinations for more information on choosing the right exposure settings.

How do I judge if my negatives are properly exposed?

A correctly-exposed negative will have some detail in its shadow areas, and its highlight areas will just permit newsprint to be read through them if the negative is placed on a newspaper in good light. These characteristics will produce an excellent photographic print with the least difficulty in a darkroom.

Want to learn more?

Many of our exposure tips and hints will not be used by some amateurs until they have become sufficiently advanced to put them into practice. So, take just those tips that you need to improve your picture-taking ability, overcoming your most-immediate problems first, then refer back later for more-advanced techniques.

One great site that include more information about exposure, how to control, and how to judge is The range of topics may seem a bit daunting for beginners, but it should not be a concern. Each topic is presented with clarity and in simple terms to ensure it will be understood.


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