Model 50 Brock Magiscope®
 
New York botanical Gardens program Magiscope®. 
 
Made very early -no Brock engraving on back.
 
No Brock engraving on eyepiece – made in 1990, special order – two stop rivets, aluminum insert probably had a stop ring.

Model #50- they use opaque specimens like flowers, ferns soil bugs, feathers.
 
Ultimate survivability. One of a kind.