Finder \Find"er\, n. (Micros.) A slide ruled in squares, so as to assist in locating particular points in the field of vision.

Source: Webster's Revised Unabridged Dictionary (1913)
 

Finder \Find"er\, n. One who, or that which, finds; specifically (Astron.), a small telescope of low power and large field of view, attached to a larger telescope, for the purpose of finding an object more readily.

Source: Webster's Revised Unabridged Dictionary (1913)