very solid mystery item 

(well it is to me anyway)

1.5kg 

google cant tell me what it is 

it's very robust and seems to filter the light , it's been suggested it could be from a photocopier ,but I'm not so sure 

the house it came from the guy was something in the military / territorial's so I wondered if it was some sort of lens from a light intensifier / night vision or something like that from a military vehicle , may be i'm just over analyzing it , I really don't know 

projector ? whatever it's from it looks mighty expensive !     

if you think you know what it is but don't want it or even if you do want it , please advise me , put me out of my misery 

ive been pondering this mystery for about 25 years   ;-)