noun
magnifying glass; loupe
A small handheld magnifying glass, often used for examining details in stamps, coins, jewelry, or watchmaking. The word 'loupe' is common in technical contexts.
from German Lupe
切手の細かい模様をルーペで観察した。
I examined the fine details of the stamp with a magnifying glass.
時計職人はルーペを目に当てて作業する。
The watchmaker works with a loupe held to the eye.