Large numerical aperture objective lens and night vision optical device using the same

摘要

A large numerical aperture objective lens is disclosed having three lens groups. In order from the object side, these lens groups include: a first lens group of positive refractive power that is formed of two positive lens elements and an achromatic set of paired lens elements formed of a lens element of negative refractive power and a lens element of positive refractive power, respectively; a second lens group of negative refractive power; and a third lens group of positive refractive power, with the surface of the third lens group nearest the object side being convex. Specified conditions are satisfied in order to provide a compact, large numerical aperture objective lens having its aberrations favorably corrected as well as to correct for shifts of focus caused by expansion/contraction of the lens barrel with changes in temperature. The objective lens of the invention is particularly suitable for use in a night vision optical device having a photoelectron amplifier tube and an eyepiece, wherein aberrations in the eyepiece are balanced by aberrations of the objective lens.