Showing papers on "Angular aperture published in 1978"

Electromagnetic field in the focal region of wide-angular annular lens and mirror systems

Abstract: The time-averaged electric energy density near the focus of a lens or mirror system with annular aperture is calculated. The distribution shows greater difference from the paraxial approximation than for the full circular aperture. The vector distribution of the polarisation after focusing greatly affects the field near the focus. In particular, a mirror with annular aperture which deflects a plane-polarised wave through a small angle gives a distribution in the focal plane which exhibits bright rings around a dark centre. The field distribution of an annular system is found to consist of just two modes of free space.

Wide angle telecentric projection lens assembly

Abstract: A wide angle telecentric projection lens system, having a long back focal distance, includes a front lens doublet, comprising negative and positive meniscus lens elements, located in front of an aperture stop, and a rear lens group on the other side of the aperture stop, the rear group comprising a rear lens doublet which includes positive and negative meniscus lens elements, the rear doublet having its curvature reversed relative to the front doublet but having an air space between its component lens elements, plus two biconvex lens elements slightly spaced from each other and from the second doublet. A beam splitting optical prism and/or similar optical element(s) may be included between the rear lens group and the object.

Tunable wide angular aperture filter by degenerate four-wave mixing

Abstract: A wide angular aperture, tunable filter device is achieved by using degenerate four-wave mixing. The apparatus utilizes two counter-propagating pump beams at substantially the same frequency to interact with an object beam, containing a spread of frequency components through a third order nonlinearity in the susceptibility of a medium. This produces a conjugate image beam formed with frequency components close to the frequency of the pump beams. By tuning the frequency of the pump beams the object beam frequency spectrum may be scanned while preserving all of the spatial information in the object beam. Apparatus for generating velocity contours of moving objects is also disclosed.

Simplified sector scan ultrasonic imaging system

Abstract: A curved transducer array or a flat array with an acoustic converging lens functions as a fixed focus physical lens and is focused near maximum range. At longer ranges the full aperture is utilized for good resolution, and at shorter ranges up to a specified fraction of maximum range improved resolution is achieved by a dynamic aperture control which increases the array aperture by steps by switching in more transducer elements. This simplified sector scanner does not require dynamic electronic focusing.

Telephoto lens with large relative aperture

Abstract: A telephoto lens with large relative aperture comprises a first converging lens group, a diverging lens group and a second converging lens group arranged in this order as viewed from the object side. The first converging lens group has two positive lens components and a negative lens component spaced from each other by an air space, the group remaining fixed when focusing. The diverging lens group has a cemented negative lens component and a negative lens component with an air space therebetween which is larger than the sum of the center thickness of the former component and the center thickness of the latter component. The second converging lens group comprises a cemented lens component and remains fixed when focusing. The first converging lens group and the diverging lens group virtually form an afocal system for an object at infinity. The diverging lens group is movable along the optical axis toward the image side for focusing upon an object at a shorter distance and also toward the object side for focusing upon an object at a longer distance.

An equal group delay waveguide lens

Abstract: Analytical and experimental results are presented on a circularly polarized waveguide lens that has much greater bandwidth than conventional waveguide lenses. This is achieved by designing the lens to have equal group delay for all rays from the focal point of the lens to the aperture plane. Haft-wave-plate phase shifters in each waveguide element are then oriented to produce a planar phase front. This results in a lens whose aperture phase distribution remains essentially constant over a much wider frequency range than in conventional waveguide lenses. A comparison with a minimum thickness conventional lens and with a phase compensated (Coulbourn) lens is made. A 46-in X band lens was built and tested over a frequency range from 7-9 GHz to confirm the bandwidth performance.

Efficient coupling of LED and spherical‐ended fiber

Abstract: A model of the coupling of a Lambertian LED and a spherical‐ended fiber is proposed and analyzed by means of geometrical optics. The system of this optical coupling can be regarded as a simple optical system which consists of a light source, a principal plane, and an aperture stop. The model analyzed is that in which a light source and an aperture stop are on the anterior and the posterior focal planes, respectively. The maximum incident angle φm into the fiber is determined from the condition that the ray passing through the anterior focal point is not obstructed by the aperture stop, which has the same diameter as the core one. According to the theoretical analysis, the coupling efficiency for the Lambertian LED and the spherical‐ended fiber is sin2φm provided that d0?dc and (dc/d0)2 sin2φm provided that d0≳dc, where d0 is the emitting diameter and dc is the critical diameter defined by the critical angle φc of the light propagation in the fiber. For two kinds of LED’s with emitting diameters of 35 and 85 μm, the coupling experiment was performed on spherical‐ended fibers which had a numerical aperture NA of 0.14 and a core diameter of 85 μm. The spherical ends of fibers were fabricated to radii r from 75 to 170 μm. A good agreement between the theoretical and experimental results is obtained. In the case that the emitting diameter is 35 μm and the spherical radius is 75 μm, the calculated efficiciency is 6.3%, three times greater than that for a flat‐ended fiber. It is shown that the coupling efficiency can be improved by using the spherical‐ended fiber with the spherical radius less than about d1/(4NA), where d1 is the core diameter. It is also shown that the maximum coupling efficiency for the LED with the emitting diameter of d0 is obtained by the fiber with the spherical radius less than about d0/(4NA).

Fixed focus exposure control apparatus with reverse spherical aberration corrective characteristic

Abstract: An improved lens arrangement is provided for use in a camera of the type having a focal plane and a subject-to-camera distance responsive effective maximum aperture limiting control arrangement operatively disposed with respect to the focal plane. The improved lens arrangement has a reverse spherical aberration corrective characteristic which operates to reduce the effective circles of confusion associated with each of the images of different subjects within a given range of distances from the camera as formed at the focal plane by the lens arrangement in combination with the effective aperture control arrangement.

Large aperture extended range zoom lens

Abstract: Disclosed is an optical design for a variable focal length lens of large effective aperture which is focusable over an extended range including the "macro" range and is provided with a high degree of correction.

Wide angle zoom lens with high zoom ratio

Abstract: A two lens group type of miniaturized zoom lens system having a minimum wide end viewing angle of 76° and a zoom ratio at least 2.3. The first or object side lens group includes at least two positive and two negative lenses with the image side lens being positive. The second or image side lens group includes at least two positive lenses facing the object. The variable aperture is mounted in front of the second lens group and the fixed aperture, which may be proportionally movable, is mounted behind the second lens group. The overall lens system satisfies the following conditions: ##EQU1## wherein: Z is the zoom ratio (Z=fT /fW), f1 is the focal length of the first lens groups, f2 is the focal length of the second lens group, fW is the focal length in the wide angle position, fT is the focal length in the telescopic or narrow angle position, and rI is the radius of curvature of the lens surface facing the object of the positive lens nearest to the image in the first lens group.

Sub-picosecond optical gating by degenerate four-wave mixing

Abstract: A high speed, wide angular aperture, spectrally selective optical gate is achieved by using degenerate four-wave mixing. The apparatus utilizes two counterpropagating pump beams to interact with a probe beam through a third order nonlinearity in the susceptibility of a medium to produce an image beam which is counterdirectional to the probe beam. The image beam is produced only during the time that the two pump beams and the probe beam are coincident in time and space in media having a fast nonlinearity. In slow media, fast gating is achieved by turning off both pump beams after the probe beam and the pump beams have interacted. This apparatus produces gate times which are not limited by the speed of relaxation of the nonlinearity in the medium utilized.

Modified gauss type lens system

Abstract: An improved Gauss type lens system having a relatively large aperture ratio is provided. The lens system comprises seven components between object and image as follows; a first positive meniscus lens element, a second positive meniscus lens element, a third negative meniscus lens element, a fourth meniscus shaped doublet, a fifth positive meniscus lens element, and a sixth positive lens element. The entire lens system is capable of providing a relative aperture of F No. 1.2, an angle of view of 50° and a back focus at least 0.7 times the overall focal length of the lens system.

Lens barrel having an aperture information transmission section

Abstract: Full and minimum aperture information is transmitted to a camera body from an interchangeable lens by coding possible combinations of the two values into various discrete single values and transmitting the single value to a decoder in the camera body. For instance, a projection may be provided on the lens barrel having a height corresponding to a particular combination of full and minimum aperture values.

Method of widening the angular field of a photographic objective lens

Abstract: A varifocal objective lens or mono-focal objective lens with a macro-focusing mechanism is provided with a concave lens component detachably mounted at the front thereof to widen the angular field of view of the objective lens while adjusting the marco-focusing mechanism to a position, where the object position for which the objective lens is focused is substantially coincident with the position of the front focal point of the concave lens component.

Low diffraction iris diaphragm for camera objective - has aperture further reduced below min. width by linearly varying, low density optical filters introduced over aperture

Abstract: The aperture plates form the diaphragm aperture and determine its variable size. The diaphragm has a device (10-14, 31-34) for linear variation of its aperture, by which the aperture plates (21-24) can be moved from a maximum aperture to a specified small aperture not producing any diffraction. when the aperture is a minimum at least two low density filters (50, 60) with linearly varying density can be swung into the aperture formed by the aperture plates (21, 24).

Inverted telephoto lens system

Abstract: A wide angle lens system of an inverted telephoto type is provided. The lens system comprises six separate lens groups comprising, consecutively from the object to the image side a negative meniscus lens element; a positive doublet; a positive meniscus lens element; a biconcave single lens element; a positive lens element and a rear positive lens element. One of the lens elements of the fifth and sixth groups is a single lens element while the other is a doublet. The lens is capable of providing an aperture ratio greater than F/2.0, a field angle of approximately 64 degrees and a back focal distance greater than the focal length of the system.