Abstract: An image synthesizing method for synthesizing a plurality of images partially overlapping with each other, having the steps of inputting a plurality of image data each corresponding to a plurality of images, extracting a matching point of duplicate areas of desired two images partially overlapping with each other among a plurality of images of the plurality of input image data, and sequentially detecting a position relationship between two images in accordance with the extracted matching point, detecting the position relationships of all images in accordance with the position relationship between two images sequentially detected by the position relationship detecting step, and synthesizing the images of the plurality of input image data in accordance with the position relationships of all images detected by the all image position relationship detecting step to form a synthesized image.

Abstract: In a projection type display apparatus for illuminating a projection original image with light from a projection light source, and projecting light transmitted through the illuminated original image using a projection lens, light reflected by a projection surface is extracted from a position at an original image side of the projection lens or in the projection lens, and the extracted light is received by a focus detection unit.

Abstract: In a retro-focus type lens divided into three lens units by the widest air spacing and the next widest air spacing, a first lens unit is disposed on a long conjugate side and has negative refractive power, and includes a negative lens and a lens provided with an aspherical surface, a second lens unit is disposed subsequently to the first lens unit and provided with a positive lens block, and a third lens unit is disposed subsequently to the second lens unit and has positive refractive power, and includes a negative lens and a positive lens.

Abstract: A retrofocus type lens having a plurality of lenses divided into three lens units, or, in the order from a screen, a first lens unit, a second lens unit and a third lens unit, wherein letting the focal length of the entire lens system be denoted by fT, and the distance from a lens surface on the side of an original image to the original image by SK,SK>0.7 fTis satisfied, and the second lens unit and the first lens unit or the third lens unit each is provided with at least one aspherical lens of which at least one of the lens surfaces is aspherical.

Abstract: A zoom lens comprising, from front to rear, a first lens group of negative power, a second lens group of positive power and a third lens group of negative power, wherein as zooming from the wide-angle end to the telephoto end is performed by moving the first, second and third lens groups, the second and third lens groups both are directed forward and the speed of movement of the third lens group is faster than that of movement of the second lens group, the zoom lens satisfying the following conditions:1<S1w/S2w<3.20.15<.vertline.f3.vertline./FT<0.432<FT/FW<5where S1w and S2w are air separations between the first and second lens groups and between the second and third lens groups in the wide-angle end respectively, f3 is a focal length of the third lens group, and FW and FT are shortest and longest focal lengths of the entire lens system respectively.

Abstract: This specification discloses a projection type display apparatus in which the lights of a plurality of display means forming images of different color component lights are reflected by or transmitted through a dichroic mirror to effect color synthesis and the synthesized lights are projected onto a screen by a projection lens. The astigmatism created by the lights being transmitted through the obliquely disposed dichroic mirror is suppressed to thereby obtain a good quality of image.

Abstract: A zoom lens is disclosed comprising, in the order from a large conjugate side, a first lens unit of positive power, a second lens unit of negative power and a third lens unit of positive power, wherein when zooming from the wide-angle end to the telephoto end, the separation between the first and second lens units increases, the separation between the second and third lens units decreases, and the third lens unit moves toward the large conjugate side, the zoom lens satisfying the following conditions:0.3<e.sub.IIW /f.sub.W <0.61.5<-(1/f.sub.I +1/f.sub.II).multidot.f.sub.W <2.00.3<-f.sub.II /f.sub.W <0.45where f.sub.W is the focal length of the entire lens system at the wide-angle end, f.sub.I and f.sub.II are the focal lengths of the first and second lens units respectively, and e.sub.IIW is an interval between principal points of the second and third lens units at the wide-angle end.

Abstract: A zoom lens includes, in succession from the greatly conjugate side to the little conjugate side, a first lens unit having negative refractive power, and a second lens unit having positive refractive power. Zooming from the wide angle side to the telephoto side is effected by at least the second lens unit being moved toward the greatly conjugate side. The zoom lens satisfies the following condition:bf.sub.w /f.sub.w >1.6,where f.sub.w is the focal length of the entire system at the wide angle end, and bf.sub.w is the distance from the last lens surface of the second lens unit to the little conjugate side.

Abstract: A projection display apparatus, which projects a magnified image onto a screen, comprises an image forming system, such as a display panel, a projector including a plurality of lenses for projecting the image onto the screen, and a decentering mechanism for decentering some lenses in the projector with respect to the optical axis. Even if the image is distorted by arrangement of the screen and the optical axis and so on, the distortion is compensated by decentering the lenses and producing a decentering distortion.

Abstract: A zoom lens includes a first lens group having a negative refractive power and having an object-side sub-group stationary during focusing and an image-side sub-group arranged to move for focusing purposes, and a second lens group having a positive refractive power and arranged on the image side of the first lens group, wherein the first lens group and the second lens group move axially at the same time and in differential relation for zooming purposes.