I am struggling to make head or tail of the two diagrams above. In the larger one it purports to show the light meter opening in the pentaprism. Not on all the through the lens SLR cameras I have owned - it isn't!*
The clue is in the camera metering type description. What camera is this diagram based upon please? A degree of writen explanation would have helped. It has always been my understanding in most later SLR's that the meter and sensor are generally placed in the lower part of the camera such as shown with the item above item 10 where it reads the light passing through a semi-silvered mirror onto the sensor. In the early SLR's with TTL metering, the sensor was in the prism but the light came via the lens, not via a peephole in the prism housing itself.
The lower diagram could show almost any early SLR which had a TTL metering system and for what detail it shows, it isn't very clear which part does what.
*In some of the manual focussing and autofocus Nikon, Pentax and possibly some other cameras, there is a small opening below the pentaprism, but this serves only to illuminate the meter reading figures/needle and has no effect on the actual metering and exposure.
