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Exposure

The darkness or lightness of an image.


High shutter speed froze this explosion's debris in mid-air
High shutter speed froze this explosion's debris in mid-air

If a beginning photographer wants to advance beyond point-and-shoot picture-taking, he or she must understand exposure.

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.


WHAT IS PROPER EXPOSURE?

If film or a digital camera's sensor receives the correct amount of light, the resulting picture reproduces the subject in all of its proper tones and colors. Such a picture is said to have been "properly exposed."

Proper exposure is essential to taking good pictures, and is determined by accurate measurement of the light falling on or reflected by the subject, using a light meter, also known as an exposure meter.

The five factors that determine proper exposure are:
1. light falling on the subject,
2. film speed or ISO sensitivity setting,
3. lens aperture,
4. shutter speed, and
5. filters used.

Proper exposure of a given scene for one photographer may not be the same for another photographer. It depends on the photographer's intended use for the image. A picture that is too dark (underexposed) or too bright (overexposed) for its end use may be just right for another photographer's purpose. “Proper exposure” refers to exposure that produces an image satisfactory to the photographer. It is therefore subjective, and it is important for photographers to realize that they can control exposure for the effect they are seeking.

A small aperture provided this image with plenty of depth of field
A small aperture provided this image with plenty of depth of field

Faster shutter speed would have prevented the blur in this night scene
Faster shutter speed would have prevented the blur in this night scene

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.

MORE THAN ONE SHUTTER SPEED/APERTURE COMBINATION WILL PROVIDE PROPER EXPOSURE

For any one accurate light meter reading, there is a range of shutter speed/aperture combinations that may be used to provide good exposure. Each combination will provide your image with a different look and characteristics. Knowing how the shutter speed and aperture combinations will affect your pictures is the key to understanding and using the concept of exposure.

The photographer must select the most suitable combination to make the image he or she desires. For example, a fast-moving subject requires a fast shutter speed to "freeze" its motion, so a lens aperture must be chosen that corresponds to the selected fast shutter speed by remaining within the range of shutter speed/aperture combinations determined by the light meter.


AN EXAMPLE

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.

A tricky play of light and shadow presents an exposure challenge.
A tricky play of light and shadow presents an exposure challenge.

Strong light and deep shadow need careful metering of the light falling on the subject only. This underexposes the background, making it go dark. Its resulting total lack of detail helps the picture by eliminating unnecessary elements.
Strong light and deep shadow need careful metering of the light falling on the subject only. This underexposes the background, making it go dark. Its resulting total lack of detail helps the picture by eliminating unnecessary elements.

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?

This section of PhotographyTips.com deals with all aspects of exposure. 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.

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.

HAVE AN EXPOSURE TIP OF YOUR OWN?

Be sure to send us your own exposure tips and pointers. If we share them with our viewers, we will be sure to give you a credit. Include an image file that shows how your tip is effective.

Proper exposure for a scene like this reflection in a lake's surface can be tricky to achieve. Expose for the light falling on the rocks but avoid metering the shadow areas. Bracket such exposures for insurance.
Proper exposure for a scene like this reflection in a lake's surface can be tricky to achieve. Expose for the light falling on the rocks but avoid metering the shadow areas. Bracket such exposures for insurance.
Further information...

Shutter speed/aperture combinations

Record your exposure settings

Lighting ratio

Bracketing exposure

Exposure Value system

Exposure compensation

Exposure latitude

Exposure meter

Overexposure & underexposure

Programmed exposure

Sunny 16 rule
Related topics...

Tips on histograms