Addition:
http://youtu.be/t2s8eLtaxVk?t=1m38s
http://youtu.be/PMDJ0bwn4sE?t=3m45s
You can see the back and sides of the optics (and other sensible parts like the rear compartments of the 35mm AA the russian guy is shooting in his vid) are usually protected with plates thick enough to at least negate small arms fire. The people developing this stuff know what they're doing.