Abstract: In an optical system having a lens with adjustable focal length, an adjustable aperture plate, and a light-meter device attached to the aperture plate adjustment device, apparatus for connecting the focal-length adjustment device so that the aperture opening is limited by the focal length adjustment device. Additionally, a signalling device emits a signal of the aperture opening defined by the focal-length adjusting device is smaller than the opening if the aperture plate controlled by the light-meter device. In another embodiment an additional variable aperture is located in front of the light-meter device and the adjustment device for this additional aperture is also connected to the focal-length adjustment device.

Abstract: A projector for motion pictures or slides has a varifocal objective with a positive front component, an axially slidable negative intermediate component and a fixed positive rear lens group. The front component, or at least its foremost lens member, has a lens mount which is displaceable along a track substantially transverse to the optical axis; the track may be curved with its convex side facing the projection screen. A diaphragm just behind the front component has an aperture barely exceeding the diameter of the intermediate component whereas the front component (or its transversely displaceable part) is radially extended past the diaphragm aperture so as to register with it in every position.

Abstract: A substantially afocal front attachment of variable magnification ratio, to be combined with a fixed-focus rear lens group in order to form a zoom objective, consists of two fixedly interconnected outer lens members and an axially shiftable biconvex intermediate lens member. The two outer lens members are negative menisci turning their convex sides toward the intermediate lens member. The objective has a varifocal ratio close to 2:1.

Abstract: A varifocal forward lens group of a camera objective, with a pair of axially shiftable negative components bracketed by a pair of substantially fixed positive components, has its negative third component more widely separated from its positive fourth component in a wide-angle position of minimum overall focal length than in a telephoto position of maximum overall focal length. The effective diameter of that third component is just large enough to let a bundle of axially incident light rays fully illuminate the fourth component in the wide-angle position, with less than full illumination in the telephoto position. The positive first component is also just large enough to provide full illumination of the effective area of the third component by axial rays in the telephoto position.

Abstract: A zoom objective is disclosed which consists of a varifocal front lens group and a fixed rear lens group, the front lens group comprising a stationary first component of positive refractivity, axially shiftable second and third components of negative refractivity, and a stationary fourth component of positive refractivity separated from the rear lens group by a reflex prism adjoining a diaphragm space. The assembly of third and fourth components, prism and rear lens group can be selectively combined with various first and second components to provide zoom objectives of different varifocal ratios.

Abstract: A camera of the reflex type comprises a view finder with an achromatic finder objective, an eyepiece, and an interposed inverting lens group. The finder objective includes a negative-meniscus lens of relatively low Abbe number and a biconvex lens of relatively high Abbe number. The negative-meniscus lens, which has a concave forward surface, may be air-spaced from the biconvex lens or may be cemented thereto to form a doublet; in the latter instance the doublet is preceded by a positive, biconvex or planoconvex, front lens.

Abstract: A pancratic wide-angle objective comprises a stationary negative front component in the form of a single meniscus with a convex forward surface, an axially movable intermediate component consisting of a biconvex lens, and a stationary multilens positive rear component separated from the front component by an airspace greater than the focal length of the latter. The individual focal lengths of the front, intermediate and rear components have absolute values in a ratio of approximately 4:5:3.