>>3558774pretty common in film days in compact cameras. You could not use contrast detect autofocus and phase af was for SLR.
so it has an ultrasonic emitter and receiver and it would measure the distance to the subject with soundwaves.
if you tried to shoot through glass you would get the wrong focus, because it would focus on the glas and not the subject behind the glass.
check out the two thingies next to the viewfinder: one is the transmitter, one the receiver
