Nikon N90s: How Does 3-D Matrix Metering Work?
(From Nikon N90s brochure, © Nikon Inc., 1996)
With 3-D Matrix Metering, the camera's computer analyzes the following data to determine exposure:
- Brightness data from each of eight segments (configured in various combinations)
- Contrast among segments
- Distance Information from the D-type Nikkor lens in use
- Focus status data from the camera's AF system (during composition and after recomposing with AF-lock)
On the basis of these four types of data, the N90s's computer selects the most suitable algorithm to use for exposure calculations from many stored in camera's memory. (Note: an algorithm is a set of procedures for solving a mathematical problem.)
First, the computer calculates the exposure value for the scene in two ways: as an eight-segment pattern and as a five segment pattern (center segments are regarded as one segment). Then both exposure values are combined to offer the best possible exposure according to Data #1, #2, #3 and #4.
Distance Information (#3) is used to balance the readings, for example, if the subject is close to the camera, the computer biases its calculations in favor of the five0segment reading: because when shooting a subject nearby, especially in extreme close-up photography, too much segmentation may mislead the meter because of high magnification ratio.
Eight-segment matrix Metering also works with a non-D-type AS or AI-P Nikkor lens, but without using data #3.
Finally, focus data (#4) determined if the subject is in the center of the frame or off-center For example, if the amount of defocus detected is not great, the computer judges that the main subject is in the center and the information from the center-segments is appropriately weighted. If the defocus amount is large (out-of-focus), the computer judges that the main subject is not in the center (as when focus lock is used for recomposing off-center) and the information from the peripheral segments is weighted (based on their relative brightness and contrast). When Focus Lock is used, if the meter judges the scene to be strongly backlit or the main subject to be strongly illuminated against a dark background, data detected prior to recomposition is also considered for final evaluation. The foregoing also applies to manual focusing with Electronic Rangefinder.
In addition, fuzzy-logic algorithms are employed for smooth data processing and to prevent sudden changes of exposure in continuous shooting.