What is this component? (range finder)
The big circular parts likely is ultrasonic transducer as used in instant camera. 

http://www.uoxray.uoregon.edu/polamod/

https://www.google.com/?gws_rd=ssl#q=polaroid+ultrasonic+ranging+module&amp;revid=399558007&amp;safe=off

Working principle is same as modern unit, easily available at a few US dollars. The transducer does NOT work by itself, needs the associate PCB to work.