Abstract: A zoom lens comprising a negative first lens unit, a positive second lens unit, and a negative third lens unit and having a small backfocus, in which a refracting power of the third lens unit can be intensified to thereby provide a compact zoom lens. An aberration resulting from intensifying the refracting power is corrected by introducing an aspherical surface into the second lens in particular. Furthermore, the first lens unit is divided into two lens components, and the first lens unit is let out while varying a spacing between the two lens components at the time of focussing whereby focussing can be made with less extension amount from an infinite far point to a near distance while preventing degradation of aberrations.

Abstract: When a lens system is focussed at a fixed length, what range of an object is clearly photographed is determined by the focal length and F number of the lens. In order that a zoom lens which requires no focussing operation is mounted on the beginners' camera to make the focussing range as wide as possible, the focussing position need be deviated as the focal length f varies as zooming takes place. If F number is selected in the range of F.gtoreq.2.8.times.10.sup.-3 .times.f.sup.2, a performance camera can be realized with a zoom lens including a wide angle and having a variable power ratio of the order of 2.

Abstract: A small type zoom lens composed of 3 to 5 lenses, which is suitable for a compact camera. The lens has a telephoto type optical arrangement including a positive first lens unit and a negative second lens unit, both of the lens units being moved forward as a whole while narrowing a space therebetween during variation of power from a short focal end to a long focal end. The first lens unit has an arrangement of refracting powers substantially symmetrical with respect to a diaphragm to correct aberrations produced by the second lens unit composed of a negative single lens.

Abstract: A device for emergently relieving pressure comprises a flexible plate bent downward and having its periphery attached to the inner surface of a hatch coaming, wherein the periphery of the plate is welded to the inner surface of the coaming at appropriate intervals, and the gap between the remaining part of the periphery of the plate and the coaming inner surface is sealed by a sealant.When a specified pressure exerts on the flexible plate, the plate starts bending back upward. With the upward bending of the plate, the welds between the plate and the coaming are deformed and broken, allowing the plate to be blown off from the coaming. Thus the device, if installed on a fuel tank, serves to relieve the pressure in the tank for the maintenance of safety.