The 'camera mod' has nothing to do with the periscope camera, rather the external view camera. Its limits range and speed of motion.
As Seminole said the targets have to be 'locked' before the scope camera will activate .
Here is a handy guide "How to complete a mission by Beery"
http://www.subsim.com/radioroom/showthread.php?t=111509
BTW what ever happened to Beery ?