Abstract: An observation optical system of the present invention comprises an image erect optical system and an eyepiece optical system for observing an object image.

Abstract: The invention relates to an image-formation lens system well balanced among cost reductions, size reductions and performance improvements and an imaging system incorporating that lens system. The image-formation lens system in the imaging system is a zoom lens system that comprises at least three lens groups including a first lens group G1 of positive power, a second lens group G2 of positive power and a third lens group G3 of negative power, wherein zooming is carried out by varying the spacing between adjacent lens groups.

Abstract: A three-lens-unit zoom optical system includes, in order from the object side, a first lens unit with positive refracting power, a second lens unit with positive refracting power, and a third lens unit with negative refracting power. These individual lens units are moved toward the object side so that when the magnification of the zoom optical system is changed, extending from the wide-angle position to the telephoto position, a space between the first lens unit and the second lens unit is widened and a space between the second lens unit and the third lens unit is narrowed. In this case, the second lens unit has at least one negative lens and at least two positive lenses, and the third lens unit has, in order from the object side, a lens with at least one aspherical surface and a negative lens, satisfying the following conditions: 0.5<|f3|/h<0.8 −0.2<f3/f1<0.

Abstract: A three-lens-unit zoom optical system includes, in order from the object side, a first lens unit with positive refracting power, a second lens unit with positive refracting power, and a third lens unit with negative refracting power. These individual lens units are moved toward the object side so that when the magnification of the zoom optical system is changed, extending from the wide-angle position to the telephoto position, a space between the first lens unit and the second lens unit is widened and a space between the second lens unit and the third lens unit is narrowed.

Abstract: A zoom optical system consists of, in order from the object side, a first lens unit (G1) with a positive refracting power and a second lens unit (G2) with a negative refracting power. In magnification change from the wide-angle end through the telephoto end, each lens unit is moved toward the object side in such a manner that a space between the first lens unit (G1) and the second lens unit (G2) decreases. The first lens unit (G1) consists of, in order from the object side, a first lens component (U1) with a positive refracting power, a second lens component (U2) with a negative refracting power, and a third lens component (U3) with a positive refracting power. The third lens component (U3) consists of a cemented-lens component. Also, the following condition (1) is satisfied: fT/fW>3  (1) where fT is the focal length of the entire system in the telephoto-end position, and fW is the focal length of the entire system in the wide-angle end position.