Cameras using the System

• EOS-3 (November 1998) — 35mm film camera
• EOS-1V (March 2000) — 35mm film camera
• EOS-1D (December 2001) — APS-H DSLR camera
• EOS-1Ds (November 2002) — Full-frame DSLR camera
• EOS-1D Mark II (April 2004) — APS-H DSLR camera
• EOS-1Ds Mark II (November 2004) — Full-frame DSLR camera
• EOS-1D Mark II N (September 2005) — APS-H DSLR camera

Why this System was Innovative

The 21-zone metering system was exclusively developed for Canon EOS cameras having 45 autofocus points. It was introduced in 1998 with the Canon EOS-3, a professional SLR camera that came with several innovations. The EOS-3 features Canon's 2nd-generation Eye-Control AF, which allows the camera to track the photographer's eye looking through the viewfinder. The metering system instantly ties its exposure calculations to the autofocus point the user has selected (manually or via eye-control). Another added feature is called multi-spot metering. For high-contrast situations, the EOS-3 allows photographers to take up to eight individual spot readings across the frame. The camera then averages these readings together to achieve perfect exposure in highly complex lighting environments. It is also worth mentioning that the 21-zone metering system offers an increased low-light metering capability compared to the 16-zone system, effectively doubling sensitivity in the dark.

Metering Modes

This 21-zone metering system offers the following metering modes:

• Evaluative metering: This is an all-around metering mode suited even for backlit subjects. The viewfinder is divided into 21 metering zones. All the focusing points are linked to the evaluative metering zones. After detecting the main subject's size, position, brightness, background, front and back lighting, etc., the camera sets the proper exposure.
• Spot metering: This is for metering a particular part of the subject or scene. The metering reads only a small 2.4% portion of the viewfinder and ignores all other areas. Three options are available: (1) The default setting couples spot metering with the center of the viewfinder (zone 1). (2) The 45 autofocus points can be limited to 11 so that they are available for eye-controlled selection and manual selection. In this mode, spot metering is linked to the eye-selected or manually-selected autofocus point. (3) A feature called multi-spot metering allows the user to take multiple spot meter readings that get averaged to an ideal exposure automatically.
• Partial metering: This mode is useful when the background is much brighter or much darker than the subject. The metering is weighted at center of the viewfinder (zones 1 and zones 6-9) by about 9%.
• Center-weighted average metering: The metering is weighted at the center and then averaged for the entire scene.

AE Metering Sensor Layout

The overall sensor design is very similar to its predecessors. Support structures, connector pins, as well as the integrated circuit (IC) die are embedded inside a clear-molded package. This sensor uses a 21-zone segmented SPC (silicon photocell) as the actual light-sensitive element. Some of the IC's active area surrounding the SPC is used for signal amplification and processing. The amplification circuitry allows the camera to use auto-exposure metering even in low-light situations.

AE Metering Range

EV 0 - 20 at ISO 100.