Canon EOS 100 - Focusing

Focusing

The EOS 100 had a single BASIS (BAse Stored Image Sensor) chip, targeting the centre of the viewfinder. This was key to its two autofocussing (AF) modes: One-shot AF and AI Servo AF.

One-shot AF was used for stationary objects. Once in focus, exposure was calculated then the shutter was released. In low light or low contrast situations, the AF auxiliary light would momentarily project a series of red bands on the subject. This then enabled the AF circuits to have a subject with contrast they could focus onto.

AI Servo AF was used for moving objects. The lens would continuously refocus on the object in the centre of the viewfinder whilst the shutter release button was pressed half-way. Once the shutter release button was fully pressed, the exposure was calculated then the shutter released.

Depth of field preview could be enabled via a custom function. If enabled, the aperture would reduce to show the depth of field every time the AE Lock Button was pressed.

• View presented to the photographer

• Auxiliary light – bands of red light shone onto subject to give contrast for autofocus circuits to operate