Abstract: A zoom lens construction of the type including from the object side a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. The first and third lens groups being held stationary, the second lens group being movable along the optical axis for zooming operation, and the fourth lens group being movable to maintain a plane of focus in compensation for variations in subject distance and shifts of focal point resulting from zooming operations. The zoom lens comprising a stop provided between the second and third lens groups movably along the optical axis, and arranged to be located closer to the imaging plane at the longest focal length of a zooming range than at the shortest focal length thereof.

Abstract: A hologram recording system useful for recording holograms for use on a film strip tape in an optical retreival system is disclosed. The recording system permits accurate centering of a selected one of a series of frames. A hologram for use on a film strip tape is recorded with interfering divergent beams of .lambda..sub.1 wavelength coherent wave energy for readout with a plane wave of .lambda..sub.2 wavelength coherent wave energy to provide a reconstruction in a plane spaced a preselected distance Z.sub.3 from the plane of the hologram record being read out. The respective distances Z.sub.1 and Z.sub.2 of the effective optical crossovers of the two divergent recording beams from the plane of the hologram recording medium are uniquely functionally related to the preselected distance Z.sub.3 and the ratio .lambda..sub.2 /.lambda..sub.1.

Abstract: An apparatus for measuring an optical property of an object such as its optical density, is disclosed. The apparatus comprises a light flash source, a photodiode coupled to a current-voltage transducer, a reference voltage source, a voltage comparator for comparing the reference voltage and voltage of the transducer, and a clock pulse generator and pulse counter triggered by the light flash source. The comparator compares the voltage from the transducer and the reference source, and disables the counter when the transducer voltage level drops below the reference voltage level. The apparatus relies upon the fact that the intensity of light emitted by the light source decays as a function of time, including a region where the intensity decays in an exponential function of time. By appropriate selection of the apparatus component parameters, the apparatus will produce a data response equal to the optical density without the need for additional logarithmic conversion circuitry.

Abstract: Valid signals from a cell in a centrifuge rotor are distinguished from extraneous signals by passing the signals through circuits which compare the amplitude and duration of the signal with the minimum expected values for those signals. Signals having the desired amplitude and duration are passed to the appropriate recorder which can be selected by a switching mechanism actuated by a circuit triggered at the release of the signal from the duration comparison circuit. The duration comparison circuit counts signals emitted from the rotor as it rotates and hence will operate over a wide range of speeds of rotation.

Abstract: A method of testing fibrous elements for their ability to effectively coalesce and separate water from an impure petroleum compound selected from the group consisting of crude oil and distillate fractions thereof. The method comprises introducing a reproducible emulsion consisting essentially of water and a substantially pure organic solvent into contact with a fibrous, coalescer element contained in a test zone. Separate streams of coalesced water and organic solvent are withdrawn from the zone. The predominant stream is passed between a source of light and a light-measuring means. The intensity of the light received by the light-measuring means is indicative of, and used as, the criterion for determining the acceptability of the coalescer element.