Canon EOS 55 - Page 46

Part 2: Technical Information
1) Eye-Controlled Autofocus System Components
Figure 2-1 shows the basic components of the Eye-Controlled Autofocus system.
Infrared-emitting diodes (IRED) illuminate the eye. The IR reflected from the eye enters
the camera where the dichroic mirror reflects it upward to a condenser lens through
which an image of the eyeball is projected on the Eye-Controlled Autofocus BASIS.
Although this camera has a different optical system layout, a dichroic mirror, a BASIS
instead of a CCD, and more IREDs (8 instead of 4). it retains the basic principles used in
the EOS 5 / A2E.
~--r•entaprism
Eyepiece lens 1
Dichroic mirror
Fig. 2-1 Eye-Controlled Autofocus system
Eye-Controlled
Autofocus BASIS
Image-forming lens
IREDs (8)
• Dichroic mirror: Serves the same function as the beam splitter in the EOS A2E.
It has a special coating which reflects only infrared wavelengths. It directs the
infrared wavelengths to the Eye-Controlled Autofocus BASIS and passes the visi-
ble light straight through to the eyepiece.
Figure 2-2 shows the components of the Eye-Controlled Autofocus unit.
As shown in Fig. 2-3, the infrared illumination system has eight infrared-emitting diodes
(IREDs) on the eyepiece frame. They emit an infrared wavelength of 880 nm. As shown
in Table 2-3, the IREDs function to detect whether eyeglasses are worn and whether the
picture is framed horizontally or vertically.
2-2