Abstract: A changeover type variable magnification optical system whose focal length is changed by locating an auxiliary lens on the image side of a master lens assembly. The system satisfies following inequalities of:0.2<f.sub.2 /f.sub.1 <0.71where f.sub.1 and f.sub.2 are the effective focal lengths of the master lens assembly and the auxiliary lens, respectively. The auxiliary lens is constructed include of at least one aspherical lens surface.

Abstract: A zoom lens including a first lens unit of positive power and a second lens unit of negative power with the axial separation therebetween varies to bring about zooming. The first lens unit includes at least one positive lens and at least one negative lens and the second lens unit consists of a forwardly concave negative meniscus lens, thereby making the lens system small.

Abstract: A magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer provided on said support, said magnetic recording layer comprising a ferromagnetic powder dispersed in a binder, which is characterized in that said binder comprises a polyurethane resin which has a repeating unit derived from diol having the formula (I); ##STR1## in which R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different from each other, each of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 is any one of a hydrogen atom, a saturated or unsaturated aliphatic group having 1-5 carbon atoms, an aromatic group and a cyclic aliphatic group, and at least three substituents among R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are not hydrogen atoms; and l, m, n and p are independently integers of 1-3, 0-2, 1-3, and 1-3, respectively.

Abstract: Disclosed herein is a electrophotographic photoreceptor having high sensitivity and excellent durability. The photoreceptor has a photosensitive layer which contains an azo compound having the tetraphenylthiophene or tetraphenylthiophene-1,1-dioxide skeleton.

Abstract: Disclosed herein is an electrophotographic photoreceptor having high sensitivity and excellent durability. The photoreceptor has a photosensitive layer which contains at least one bisazo compound having the 2-phenyl-benzooxazole skeleton.

Abstract: A magnetic recording medium is disclosed, comprising a non-magnetic support having provided on one side thereof a magnetic recording layer comprising a binder having dispersed therein fine ferromagnetic particles and on the other side thereof a backing layer, wherein at least one of said magnetic layer and backing layer contains (1) a vinyl chloride resin having --SO.sub.3 M (wherein M is Li, Na, or K) groups and epoxy groups, and (2) polyurethane as binders. The medium has reduced output variation and improved running durability.

Abstract: An abrasive tape comprises a flexible substrate, and an abrasive layer overlaid on the flexible substrate by applying an abrasive coating composition prepared by use of abrasive grains and a binder onto the flexible substrate and drying the applied abrasive coating composition. The binder contains a vinyl chloride resin having a --SO.sub.3 M group, where M represents Li, Na or K, and an epoxy group, a resin having, at a side chain thereof, at least one polar group selected from the group consisting of--SO.sub.3 M, --OSO.sub.2 M, --OSO.sub.3 M, --COOM, and ##STR1## where M represents H, Li, Na or K, M.sub.1 represents H, Li, Na, K or an alkyl group, and M.sub.2 represents H, Li, Na, K or an alkyl group, and a polyisocyanate.

Abstract: A magnetic recording medium is described, comprising a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic fine particles dispersed in a binder including a polyurethane resin containing (1) as a main polymer chain a polyester polyol containing an alcoholic and acid components comprising at least one of (A) at least one alcoholic component selected from alicyclic divalent alcohol and aromatic divalent alcohol in an amount of 50 mol % or more based on the total amount of alcoholic components or (B) at least one acid component selected from alicyclic dicarboxylic acid and aromatic dicarboxylic acid in an amount of 50 mol % or more based on the total amount of acid components, and (2) at least one polyisocyanate selected from tolylene diisocyanate, diphenyl-methane-4,4'-diisocyanate, isophrorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and p-phenylene diisocyanate in an amount of 5 mol % or more based on the total amount of all alcoholic components and all acid compo

Abstract: An objective lens comprising a front lens group of positive power followed by a diaphragm, and a rear lens group of positive power axially movable for focusing and comprised of a plurality of members with the strongest diverging surface of concave curvature being arranged toward the front of the lens.

Abstract: In a magnetic recording medium such as a video tape comprising a nonmagnetic support and a magnetic recording layer provided on the support, said magnetic recording layer comprising a binder and a ferromagnetic powder dispersed therein, the improvement in which:the magnetic recording layer comprises a fatty acid ester lubricant and a lubricant other than the fatty acid ester lubricant;the binder is composed of a resin component comprising a resin containing a repeating unit which has a polar group and having a glass transition point of not lower than 50.degree. C., and a resin containing a repeating unit which has a polar group and having a glass transition point of lower than 50.degree. C; andat least one resin of the resins contains a repeating unit having a polar group such as --SO.sub.3 M, --OSO.sub.3 M or --PO(OM').sub.2, wherein M is hydrogen or an alkali metal atom, and M' is hydrogen, an alkali metal atom or a lower hydrocarbon group.

Abstract: A magnetic recording medium comprising a nonmagnetic support and a magnetic recording layer provided on the support, said magnetic recording layer comprising a binder and a ferromagnetic powder dispersed therein, which is characterized in that said binder is composed of a resin component comprising:a vinyl chloride copolymer containing a repeating unit having at least one polar group selected from the group consisting of --SO.sub.3 M, --OSO.sub.3 M, --COOM and --PO(OM').sub.2, wherein M is hydrogen or an alkali metal atom, and M' is any one of hydrogen, an alkali metal atom and a lower hydrocarbon group, and a repeating unit having an epoxy group; anda polyurethane resin containing a repeating unit having at least one polar group selected from the group consisting of --SO.sub.3 M, --OSO.sub.3 M, --COOM and --PO(OM').sub.2, wherein M and M' have the same meanings as defined above.

Abstract: A conversion lens for attachment to the rear of a master lens to increase the focal length of the entire system, includes a positive lens, and a negative lens positioned on the image side of the positive lens, wherein at least one of the lens surfaces of the positive lens and the negative lens is an aspherical surface.

Abstract: A view finder having, from front to rear, a first lens unit of negative power, a second lens unit of positive power and a third lens unit of negative power, the second lens unit being moved axially forward as the magnification varies from the smallest to the largest value, while the first lens unit is moved to compensate for the diopter shift resulting from the variation of the magnification.

Abstract: A magnetic recording medium is described, comprising a non-magnetic support having provided thereon a magnetic layer including ferromagnetic powder and a binder comprising a polyurethane resin having a metal salt group of sulfonic acid and vinyl chloride/vinyl acetate-based copolymer containing from 0.2 wt. % to less than 1.5 wt. % of maleic acid. The magentic recording medium has reduced deterioration of the video S/N ratio under high temperature and high humidity.

Abstract: A variable power finder having an objective lens of positive refracting power comprising a first lens unit of positive refracting power movable along an optical axis and a second lens unit releasably attached to the first lens unit in axial alignment, wherein a real image to be observed is formed by the objective lens.

Abstract: Provided are novel dichroic azo dyestuffs, which contain skeletons represented by the following general formula: ##STR1## at one terminals of the long axes of the molecules of the azo dyestuffs, and liquid crystal compositions containing the dichroic azo dyestuffs in forms dissolved in liquid crystals. These dichroic azo dyestuffs have large dichroic ratios and high durability, and their compositions are employed as useful display devices.

Abstract: A magnetic recording medium is disclosed which comprises a non-magnetic support having coated thereon a magnetic layer comprising a magnetic substance and a binder comprising a cellulose derivative, a polyurethane resin and a polyisocyanate, the non-magnetic support having a heat shrinkage of about 0.15% or less and the water content of the medium being at least about 0.35% by weight.

Abstract: A magnetic recording medium is described, comprising a non-magnetic support having provided thereon a magnetic layer having magnetic particles being ferromagnetic hexagonal crystallized tabular shape particles having an axis of easy magnetization in a direction vertical to a flat surface thereof, said binder being present in an amount of from 10 to 30 wt % based on the weight of the magnetic particles, and said binder comprising a polycarbonate polyurethane being present in an amount of from 20 to 60 wt %, a vinyl chloride and vinyl acetate type copolymer being present in an amount of from 20 to 70 wt %, and a polyisocyanate being present in an amount of from 10 to 60 wt %, based on the total amount of binder.

Abstract: In the disclosed zoom lens, a positive front lens unit and a negative rear lens unit are moved forwardly axially in differential relation to vary the overall focal length from a minimum to a maximum value, while a positive middle lens unit is kept stationary during the variation of the focal length. A diaphragm determining the F-number is positioned at a fixed point between the front and rear lens units.

Abstract: In the disclosed finder, an auxiliary lens for changing the magnification power is inserted into the space between an objective lens and an eyepiece. The size of the viewfield frame is simultaneously changed to maintain a constant percentage of the viewfield of the finder. The required rate of change of magnification power that the auxiliary lens must attain to leave the size of the viewfield frame of the finder unchanged can be reduced with the advantage of minimizing the bulk and size of the finder.