OBJECTIVE LENS DEVICE TO BE USED AT EXTREMELY LOW TEMPERATURE

摘要

PURPOSE:To prevent an objective lens from being unloaded from a barrel even if the lens is repeatedly used and to hold airtightness between a barrel and the objective lens efficiently by fixing the objective lens body to the barrel through a soft metal layer or a soft metal alloy layer. CONSTITUTION:A holder 4 is airtightly loaded to the periphery of an end part of an image guide on the light transmitting side and engaged with one end side of the barrel 1 and its outer peripheral part is airtightly fixed to the inner periphery part of the barrel 1. The objective lens body 3 is regidly fixed to the inner surface of the barrel 1 through a soft metal layer, i.e. an indium layer 5, which is arranged between the peripheral edge part of the body 3 and the inner periphery of the barrel 1. The soft metal or soft metal alloy, e.g. indium, lead or lead-tin alloy, is not almost reduced at its mechanical strength even if it is kept at an extremely low temperature such as about 4.2K, and has the coefficient of thermal expansion close to that of glass constituting the lens body 3. Even if the objective lens device is used for a long period at the extremely low temperature or used repeatedly between the room temperature and an extremely low temperature, the lens body 3 is prevented from being unloaded and the airtightness between the objective lens body 3 and the barrel is not lost.