Main Features; Finder; Viewfinder Optics - Canon A-1 Repair Manual

4. Main Features
4.1 Finder
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Reversing the current trend to more and more complicated
viewfinders with exposure information encroaching into the
field of view from every direction, the A-I viewfinder
shows the field of view alone in a dark field. When the
shutter button is pressed, the exposure information appears
in neat digital form of red seven segment LEDs below the
field of view if you wish to view it.
(1) Viewfinder Optical Design
A special optical plastic is used to make the prism
which reflects the image of the LED's thru the penta-
prism into the eyepiece. The LED's are located below
the prism, well away from the SPC so they do not
affect its reading.
Fresnel lens
SPC
Image guide prism
Fig. I Viewfinder Optics