Abstract: A zoom lens comprising, as viewed from the side of a photographing object, a first lens group, which is positive and is provided for focusing, including a positive lens formed by joining a negative lens and a positive lens together and a positive meniscus lens; a second lens group, which is negative and is provided for variation, including a negative lens and another negative lens formed by joining a negative lens and a positive lens together; a third lens group, which is provided for compensation, including a positive lens formed by joining a negative lens and a positive lens together; a fourth lens group which is positive and is provided for image formation; and a fifth lens group which is weakly negative, the third lens group drawing a concave locus toward the object side as the second lens group moves in the direction of an optical axis. The fourth lens group is composed of two positive meniscus lenses closedly adjacent to each other and a biconcave lens disposed apart from these meniscus lenses.

Abstract: In a diaphragm device for use in an optical instrument such as a camera and having two or more diaphragm blades movable across an imaging path of rays and arranged in axially displaced relation from each other to define a common aperture of variable size, there is provided means formed in a portion of at least one of the diaphragm blades to substantially either eliminate or reduce the axial displacement between the diaphragm blades at a relatively small aperture region, whereby the distribution of light energy is made uniform over the entire area of the image.

Abstract: A zoom lens system comprising five lens groups of which the first, third and fifth groups are convergent, the second group is divergent, and the fourth group is a divergent doublet consisting of convergent and divergent elements cemented together, the cemented contact surface being concave toward the front, in which the second group is axially movable to effect magnification variation, and the third group is axially movable forward and then rearward when zooming the second group from an extreme focal length range to the other, said zoom lens system being characterized by the following relationships in combination:0.6f.sub.w < -f.sub.2 < 0.8f.sub.w 1. ##EQU1##15 < V.sub.4convex - V.sub.4concave 3.0.01 < N.sub.4concave - N.sub.4convex < 0.08 4.0.03f.sub.w < -R.sub.4B < 0.4f.sub.w 5.f.sub.45 < 0 6.Wherein f.sub.w is the shortest focal length; f.sub.T is the longest focal length; M is the magnification ratio (f.sub.T /f.sub.w); fi is the focal length of the i-th group; f.sub.