Abstract: A retrofocus lens system comprises, in order from a large conjugate side: a first lens group having a negative refracting power and including a plurality of lens elements; a second lens group having a positive refracting power; and a third lens group having a positive refracting power. Each of the lens elements of the first lens group has a negative refracting power. Following conditional expressions (1) to (3) are satisfied:1.3<D.sub.1 /f<1.8 (1)0.7 <f.sub.2 /f.sub.3 <1.1 (2)1.1 <.vertline.f.sub.1 .vertline./f<1.6 (3)where D.sub.1 is air gap between the first lens group and the second lens group, f.sub.1 is a focal length of the first lens group, f.sub.2 is a focal length of the second lens group, f.sub.3 is a focal length of the third lens group, and f is a focal length of whole lens system including the first to third lens groups.

Abstract: A projection type display apparatus incorporating a light receiver or a light transmitter, in which the light signal is received or transmitted through a screen or condensing lens disposed in its vicinity, and hence the luminous flux utility efficiency is high.A projection type display apparatus capable of preventing deterioration of picture quality due to difference in color in the projection units, and the best picture quality is realized even when the projection lenses for different colors are composed of nearly same components.

Abstract: A projection lens unit includes, in accordance with the order of disposition from a screen side, a first lens group including a positive meniscus lens, a second lens group including a double convex lens, and a third lens group which corrects curvature of field, wherein the third lens group has two concave lenses. A projection lens unit includes, in accordance with the order of disposition from a screen side, a first lens having a positive meniscus form, a second lens having a negative meniscus form, a third lens which is double-convex lens having a light gathering function, a fourth lens which is disposed near the third lens and is a double-convex lens having a positive power, a fifth lens provided at its central portion with a convex surface directed to a screen and provided at its peripheral portion with a concave portion directed to the screen, and a sixth lens having a concave surface directed to the screen, wherein each of the second, fourth and fifth lenses has at least one aspherical surface.

Abstract: A projection display apparatus comprises an image source having a rectangular image-displaying surface; a projecting lens assembly for magnifying and projecting the image onto a screen; and light-obstructing plate disposed in the vicinity of the nearest lens element of the projecting lens assembly to the image source. The light-obstructing plate is disposed in such a position that 0.1.ltoreq.R.sub.1 /R.sub.2 .ltoreq.0.8 where R.sub.1 is a radius of optical-axis light which is emitted toward the screen from a central point on the image-displaying surface through which the optical axis of the projecting lens assembly passes, and R.sub.2 is a radius of effective light which is emitted toward the screen from the image-displaying surface.

Abstract: A projection lens system for projecting an enlarged image onto a display screen front an image appearing on a faceplate of a cathode ray tube utilizes at least six lens groups. The first lens group, from an end closest to the display screen, is in a form of a meniscus having a negative power. The second lens group has a weak positive power and a convex surface towards the display screen. The third lens group has a strong positive power. The fourth lens group is bi-convex and has a strong positive power. The fifth lens group has a weak positive power. The sixth lens group has a negative power and a pronounced concave surface away from the display screen. The second and fifth lens groups each are made with plastic lenses with at least aspheric surfaces on one side.

Abstract: A projection type display apparatus comprising three projection units for projecting red, green and blue images, each having a constitution wherein a holding member for holding a CRT and a holding member for holding a projection lens are separately constituted and these holding members are connected liquid-tightly by means of a soft packing sheet, while a space surrounded by the holding members and the packing sheet is filled with a coolant liquid.

Abstract: A projection lens system has a first lens to a sixth lens which are serially arranged in this order from a screen side. The first lens has a meniscus configuration in which a convex surface is directed toward the screen side and the power of the lens changes from positive to negative from the optical axis toward a peripheral portion of the lens. The first lens has two aspherical surfaces. The second lens has a positive power meniscus configuration in which a convex surface is directed toward the screen side. Both surfaces of the second lens are aspherical. The third lens has a positive power meniscus configuration in which a convex surface is directed toward the screen side. The fourth lens is disposed close to the third lens and has two convex surfaces. The fifth lens has a positive power meniscus configuration in which a concave surface is directed toward the screen side. Both surfaces of the fifth lens are aspherical.

Abstract: In a projection television system having display elements displaying images of respective colors, a screen on which a color image is formed by magnifying and synthesizing the images of the respective colors, projection lenses for magnifying the images on the respective display elements and projecting them onto the screen thereby to form the color image, with the optical axis of the projection lens for a first color being disposed at a right angle to the screen and the optical axes of the projection lenses for second and third colors being disposed at an angle with respect to the optical axis of the projection lens for the first color, color imbalance is reduced. This is achieved by disposing the projection lenses for the second and third colors so that their optical axes are incident on a point different from the point at which the optical axis of the projection lens for the first color is incident.