Camera Strip Down 6 - Mirror

I am fast reaching the end of my camera strip down. This is the rear of the main mirror and as you can see there is supplementary mirror which covers the cross-shaped unmirrored (ie. clear glass) centre section of the main mirror when you are viewing the image but folds back speedily to allow sufficient light through for the camera autofocus to function. This process  of viewing the image, allowing for autofocus and then the mirror lock-up when you capturing the image on the sensor has to operate to extremely critical time limits.