Abstract: The invention provides an ultra-wide field eyepiece for microscopes, in which such off-axial aberrations as the curvature of field, astigmatism and coma are well-enough corrected at a field number as large, as 26.5, and in which the flatness of the image surface is degraded even when the entrance pupil position varies, and which comprises, in order from the entrance side, a first lens unit G1 of negative refracting power, a second lens unit G2 of positive refracting power, a third lens unit G3 of negative refracting power, a fourth lens unit G4 of positive refracting power and a fifth lens unit G5 of positive refracting power with the surface having a stronger curvature facing the entrance side, said third to fifth lens units being located in the rear of an intermediate image plane.

Abstract: An eyepiece lens system comprising, in the order from the side of incidence of rays, a first lens unit having positive or negative refractive power as a whole and a second lens unit having positive refractive power as a whole, said eyepiece lens system having little aberrations, image surface flatness excellent to the marginal portions of visual field, a high eye point and a wide visual field.

Abstract: An objective lens system comprising four pieces lens arranged from a light source side, in order, a cemented lens which has a convex first lens and negative second lens cemented with each other, a convex third lens and a positive meniscus forth lens where convex surface thereof is faced toward the light source side.

Abstract: In a finder optical system provided separately from a taking lens system, an objective lens system forms a primary image which is an inverted image of a subject, a relay lens system erects the primary image formed by the objective lens system to form a secondary image which is an erecting image and can change the size of the secondary image, and an ocular enlarges the secondary image formed by the relay lens system and can change the enlargement ratio.The finder optical system is useful for a camera constituting the trimming system.

Abstract: The present invention provides a variable magnification viewfinder optical system, comprising from the object side: objective lens group of a positive refractive power, including a first lens unit of a negative refractive power and a second lens unit of a positive refractive power, said first and second lens units being shiftable along the optical axis of the optical system for changing the magnification of the optical system; condenser lens group of a positive refractive power; and eyepiece lens group of a negative refractive power; wherein the objective lens group forms a real image of an object and the real image can be observed through the eyepiece lens group; and wherein the optical system fulfills the following conditions;-0.09/mm<1/f.sub.1 <-0.03/mm0.04/mm<1/f.sub.2 <0.11/mm-0.1/mm<fe/(f.sub.1 .multidot.f.sub.2)<-0.035/mmwherein: f.sub.1 represents focal length of the first lens unit of the objective lens group in millimeters; f.sub.