Creating better pictures: Exposure metering systems

Exposure Metering Systems

Light is the essence of photography. How does a photographer know how to measure the light that exposes a frame of film? The answer is to be found in exposure metering systems.

Such systems built into most of today's single-lens reflex (SLR) cameras measure light through the lens to determine exposure accurately. Through The Lens (TTL) system light measurement encompasses Matrix Metering (a function that may differ in name from manufacturer to manufacturer), Center-Weighted Metering, and Spot Metering, depending on the part of the image being analyzed.

Nikon's latest autofocus SLRs are available in models that allow selection among these three metering modes.

Exposure Modes
Matrix Metering
This most common of AF SLR metering method, also called multi-pattern metering, divides the finder image into multiple regions, then employs an internal microcomputer (CPU) to detect and process data for determining optimal exposure. The CPU analysis algorithms, based on data from tens of thousands of shots including back-lighting data, are applied to automatic exposure calculation that perfectly suits the situation at hand.

Note 1: For superior metering precision, 3D multi-pattern metering introduced in the Nikon F90 accounts for distance information provided by the D-type AF Nikkor lens.

Note 2: The top-of-the-line Nikon F5 lets you select 3D Color Matrix Metering when using the standard DP-30 Multi-Meter Finder. This uses a newly-developed 1005-pixel Red-Green-Blue (RGB) sensor to collect information on subject coloration, calculate exposure, and provide conventional metering information.

Example 1

Advantage
Provides optimal exposure even for backlit scenes or those with dramatic variations in brightness, making it handy for most situations.

Center-Weighted Metering
Light is measured with priority given the center of the image -- perfect for when the main subject is framed in the middle of the picture.

Note 3: Some Nikon SLR cameras feature a large 12mm-diameter circle marked in the center of the viewfinder image, and weight this region 60-75% in metering.

Note 4: It is possible to customize Center-Weighted Metering settings, including metering area and method, using a top-of-the-line Nikon F5 camera with Nikkor lens featuring built-in CPU.

Example 2

Advantage
This is handy when the image center is bright and the periphery is dark, or when you want to make the center of the picture lighter than its surroundings. It is not suitable when the key subject is at an edge or off-center of the image.

Spot Metering
This mode meters only a specific region in the center of the image, making it suitable for shooting backlit or high-contrast subjects, or situations in which it is difficult to determine exposure settings accurately.

Note 5: Many Nikon SLR cameras feature a small circle in the viewfinder screen, measuring from about 4 to 6mm in diameter, depending on the model (1.5 to 3.3% of image area). In this type of metering, only the area inside this circle is measured (100% weighting).

Note 6: When the top-of-the-line Nikon F5 camera is used with the standard EC-B finder screen and a Nikkor lens with built-in CPU, the metered spot area corresponds to focus area selected. Five focus areas are situated in a cross-type configuration.

Example 3

Advantage
This is handy for spot-lighted subjects, such as those seen in theaters, or when only a specific point in the image is to be exposed.