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Built-in light meters

In-camera meters can be simple or complex


Just about every camera today - digital or film - has a built-in exposure meter.
Just about every camera today - digital or film - has a built-in exposure meter.

The exposure meter built into your camera’s body is a reflective-light meter - sometimes also called a reflection meter. The meter's display is usually shown in the vewfinder, often as a moving needle, red LEDs (light-emitting diodes) or a liquid crystal display (LCD).

Many photographers believe that reflected light readings provide them with more chance to evaluate individual areas of the subject than do incident light readings.

TYPES OF REFLECTIVE METERS

Your camera's light meter (whether your camera is a film camera or a digital camera) may be an averaging meter, a center-weighted meter, a zone segment system or even a spotmeter, and certain cameras have two, three or all of these types built in.


METERS IN NON-SLR CAMERAS

Non-SLR (non-single lens reflex) cameras usually have the metering system externally located, whereas most single lens reflex cameras have built-in TTL (through the lens) metering systems. The two main advantages of TTL systems is that they measure light only from the image area, regardless of the lens in use, and they provide accurate light measurement when filters are attached.

AVERAGING METER

This type of exposure meter reads the entire scene as shown in the viewfinder, averaging the light reflected from all objects within its field of view to come up with an exposure that is usually suitable for average shooting situations. (The exposure is based on the meter being calibrated for a tone with 18% reflectance regardless of the subject's shade.) However, if precise metering is required, an averaging meter will not always do the job since the photographer can’t determine how much the meter is weighting areas within the scene.

When the lighting is fairly uniform across the entire viewframe, the averaging meter will easily provide accurate readings for proper exposure.
When the lighting is fairly uniform across the entire viewframe, the averaging meter will easily provide accurate readings for proper exposure.

With the light falling mainly on the subject in the center of the frame, this scene presents a perfect opportunity for center-weighted metering for proper exposure.
With the light falling mainly on the subject in the center of the frame, this scene presents a perfect opportunity for center-weighted metering for proper exposure.

CENTER-WEIGHTED METERING

Center-weighted or center-bias exposure meters have a high percentage of the meter’s sensitivity concentrated in the center of the viewfinder.

These meters are useful where you want to base exposure on a specific area in the scene, achieved by centering the area in the viewfinder to take an exposure reading.

Center-weighted and averaging systems can provide incorrect exposure readings where the scene has wide-ranging light levels and tones, or a particularly bright or dark area.


ZONE-SEGMENTED METERING

Many of today’s cameras have internal microcomputers programmed to look at the four quadrants of an image and the center, and to base exposure on a reasonable guess as to what kind of subject is in the scene.

The measurement of light in different zones of the viewfinder by segmented photocells provides a great deal of scene information of use in determining accurate exposure, even for scenes that cause problems for center-weighted and averaging meter systems. Zone-segmented metering is a significant improvement over the simpler systems.

The viewfinder scene is measured, evaluated compared to stored data on patterns, and then categorized for subject type. Exposures determined in this manner are remarkably accurate, and will reliably make proper automatic exposures in extremely complex lighting situations. They will even determine if fill-in flash can be used, and will use it automatically and in the right amount when the flash is attached and turned on or when the camera has an integral flash that can be automatically-activated.

A scene that has very bright spots and dark shadows throughout can be read remarkably accurately for overall proper exposure by a zone-segmented meter.
A scene that has very bright spots and dark shadows throughout can be read remarkably accurately for overall proper exposure by a zone-segmented meter.

If you are fortunate enough to have a highly-sophisticated camera like the Nikon F5, you will probably find its automatic metering system will be more than adequate for 98% or more of your picture-taking needs.
If you are fortunate enough to have a highly-sophisticated camera like the Nikon F5, you will probably find its automatic metering system will be more than adequate for 98% or more of your picture-taking needs.

3D MATRIX METERING

Sophisticated automatic exposure metering systems in some top 35 mm cameras, such as Nikon’s state-of-the-art F5 model, have the ability to take not only the three-dimensionality of your subject but also even the colors of the scene into account in their exposure calculations. The F5's remarkable “3D Color Matrix” metering system (only one of the camera’s three types of exposure metering systems) uses scene brightness, contrast, subject distance and color distribution in calculating exposure.

OTF (OFF-THE-FILM) METERING

This is a particularly accurate form of TTL metering. The light readings are made from the actual film surface itself during exposure.


Further information...

Basic metering with your camera's meter

Advanced metering with your camera's meter

Gray card