periscope

(redirected from Vision block)
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periscope 

An optical instrument using two right angle reflectors in order to allow observation of an object from behind a shield or around an obstruction where direct vision is impossible. It has many applications, especially in the military forces (e.g. in tanks, submarines). See periscopic lens.
References in periodicals archive ?
Not only does blurred vision occur as you get older, it also happens when the windshield and side vision blocks on your armored security vehicle (ASV) get dirty, chipped or cracked.
It offers all-round and top protection against infantry weapons and fragments, with vision blocks for all round view and a top hatch to allow the gunner to ride head out when safe to do so.
Without it, the exhaust can damage the disabled tank's vision blocks, hatch covers, precleaner, and even the vulcanized rubber on the scavenger shaft.
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