Endoscope objective lens

Abstract

Abstract PURPOSE:To make the tip part of an endoscope thin and compact and to remove a distortion aberration by composing the objective of a foremost negative group, intermediate positive groups, and an endmost group including a concave surface contacting air, providing a stop between the surface which is closest to an object side among the intermediate groups and the surface which is closest to an image side, and satisfying specific conditions. CONSTITUTION:The objective is a lens system consisting of the foremost group with negative refracting power, the intermediate groups which have positive refracting power on the whole, and the endmost group which includes a lens having the concave surface in contact with an air surface and has negative refracting power while the stop is arranged between the surface closest to the object side and the surface closest to the image side among the intermediate groups, and inequalities hold. Here theta1 is the angle between an off-axis main light beam projecting from the objective and the optical axis, theta2 the angle between the off-axis main light beam and the optical axis of the off-axis main light beam which passes through the periphery of the stop and then the objective, fB the back focus, f1 the focal length of the foremost group, h1 the mean light beam height of the main light beam of the foremost group, f4 the focal length of the endmost group, h4 the mean light beam height of the main light beam of the endmost group, and (f) the focal length of the whole system. Consequently, the external diameter of the lens is decreased and the endoscope objective which has a small diameter is obtained.

Inventors

• 👤 Susumu Takahashi
• 👤 進 高橋

Bibliographic Details