One who or that which discovers.

发现者；探测器。

An extra lens on a camera to show the position of the picture to be taken.

(照相机等的)取景器。

A small telescope attached to a larger one to locate something, as a star, to be examined by the larger instrument.

【天】寻星镜(附于大望远镜而有固定视域的小望远镜)。