Abstract: A projector optical system has a reflection-type display panel, an illumination optical system for illuminating the reflection-type display panel, a projection optical system for projecting the images displayed on the reflection-type display panel onto a projected surface, and a light-deriving means for directing illumination light toward the reflection-type display panel. The projection optical system has, from the projected-surface side, a front lens unit and a rear lens unit. The light-deriving means is disposed between the front and rear lens units. Additionally, the following condition is fulfilled:-1.5<.phi.F/.phi.<-0.1where .phi.F represents the optical power of the front lens unit of the projection optical system, and .phi. represents the optical power of the entire projection optical system.

Abstract: A zoom lens system has at least three lens units. A first lens unit situated at an object side of the zoom lens system has a positive optical power. Zooming is performed by varying distances among the lens units. A camera shake compensating lens unit, including at least one positive lens element and at least one negative lens element, is provided in the first lens unit. The camera shake compensating lens unit is parallelly decentered to perform camera shake compensation. The ratio of the focal length f of the zoom lens system to the composite lateral magnification (.beta.r) of the lens units situated on the image side of the camera shake compensating lens unit fulfills a condition 30<f/.beta.r<120.

Abstract: An optical system design method determines a specific optical group having a relatively high decentering aberration error sensitivity to parallel decentering and tilt decentering, and minimizes the absolute value of the decentering aberration coefficient of that group. In a first stage, an optical system group consisting of at least one lens surface is identified which presents a problem in production because of a relatively high centering error sensitivity. A second stage calculates decentering aberration using a decentering aberration coefficient of the group identified in the first stage, and compares a decentering aberration that is obtained by the calculation with actual decentering aberration.

Abstract: In a zoom lens system that consists of a plurality of lens units and that performs zooming by varying the distances between the lens units, one of the lens units other than the lens unit disposed at the object side end includes a hand-shake correction lens unit that is decentered in a direction perpendicular to the optical axis for hand-shake correction and a fixed lens unit that is disposed on the image side of the hand-shake correction lens unit and that is kept in a fixed position during hand-shake correction. With respect to the lens element disposed at the image-side end of the hand-shake correction lens unit and the lens element disposed next to the image-side surface of the former lens element and kept in a fixed position during hand-shake correction, the relations between their shape factors and refractive powers are defined.

Abstract: A zoom lens system has at least three lens units of, from the most object side, a first lens unit having a negative optical power, a second lens unit having a positive optical power and a third lens unit, wherein the distances between the lens units are varied by moving all of the lens units during zooming. The zoom lens system satisfies the predetermined mathematical condition.

Abstract: A zoom lens system has, from the object side, a first lens unit, a second lens unit with an aperture stop, and a third lens unit. In this zoom lens system, zooming is performed by varying the distances between these lens units; focusing from the infinite distance to the closest distance is performed by moving the first lens unit toward the object side along the optical axis; image blur compensation is performed by decentering an image blur compensating lens unit included in the third lens unit.

Abstract: A zoom lens system has, from the object side, a first lens unit and a second lens unit. The first lens unit has a negative optical power. The second lens unit has a positive optical power. The second lens unit includes front and rear lens units which each have a positive optical power. The front lens unit is shifted in a direction perpendicular to the optical axis to compensate for an image blurring. The zoom lens system fulfills the condition 0<.phi.2R/.phi.2F<1.0, where .phi.2R and .phi.2F represent optical powers of the rear and front lens units, respectively.

Abstract: A zoom lens system of the present invention comprises, from the object side, a front lens unit having a positive refractive power and a rear lens unit having a negative refractive power, and performs zooming by changing the spatial distance between the front lens unit and the rear lens unit. The rear lens unit comprises, from the object side, a positive lens and a negative lens, at least one surface of said positive lens being aspherical and the Abbe number and refraction factor of said positive lens being set appropriately.