案あん内ない望ぼう遠えん鏡きょう

noun

guiding telescope

A small telescope mounted on a larger one, used to keep the main telescope accurately pointed at a target during observation or photography.

• 天てん体たい写しゃ真しんを撮とるときは、案あん内ない望ぼう遠えん鏡きょうで星ほしを追つい跡せきする。

  When taking astrophotographs, I track the star with a guiding telescope.