Showing papers on "Angular aperture published in 1982"

Synthetic Image Generation with a Lens and Aperture Camera Model

Abstract: This paper extends the traditional pinhole camera projection geometry used in computer graphics to a more realistic camera model which approximates the effects of a lens and an aperture function of an actual camera. This model allows the generation of synthetic images which have a depth of field and can be focused on an arbitrary plane; it also permits selective modeling of certain optical characteristics of a lens. The model can be expanded to include motion blur and special-effect filters. These capabilities provide additional tools for highlighting important areas of a scene and for portraying certain physical characteristics of an object in an image.

Changes in the characteristics of a Gaussian beam weakly diffracted by a circular aperture

Abstract: A Gaussian beam weakly diffracted by a circular aperture can be approximated in the far field by another Gaussian beam with slightly different characteristics. Equations giving the intensity, the divergence, and the radius of the modified beam are derived in simple practical form for experimentalists. These approximated formulas show that, even in the case of negligible power losses through the aperture, the diffracted beam characteristics may appreciably differ from those of the incident beam. In a first approximation, diffraction effects may be ignored only if the ratio a/r(0) of the aperture radius a to the l/e intensity beam radius r(0) in the aperture plane is larger than 3.

The image of a single point in microscopes of large numerical aperture

Abstract: The image of a single small hole in an opaque screen in a microscope of large numerical aperture is calculated. Both conventional microscopes and scanning optical microscopes are considered, the general trend being that the central peak is broadened, the outer rings strengthened and the minima made shallower as the numerical aperture is increased. In the conventional microscope the image is no longer independent of the illu­mination, as it is for paraxial theory.

Low sidelobe aperture distributions for blocked and unblocked circular apertures

Abstract: Low sidelobe aperture distributions are investigated for both blocked and unblocked circular apertures. Both peak sidelobe levels and wide-angle sidelobe levels are considered. For unblocked apertures, Taylor's circular aperture synthesis technique is generalized to provide control over the wide angle sidelobe decay rate. These distributions are compared to a wide variety of alternative distributions in terms of the beamwidth, aperture efficiency, and radiated power distributions achieved for a given peak sidelobe level. A comparison is also made between the sidelobe envelopes achieved by four different distributions with a fixed beamwidth. For centrally blocked apertures, it is shown that wide angle sidelobes can be reduced by employing aperture distributions with a hole in the blocked central area.

Coincidence correction in particle analysis system

Abstract: Flat beam optical sensing performed transverse of a flow aperture, of the particles passing through the aperture, directly indicates the presence of individual particles in the aperture. The indication can be used to eliminate or otherwise modulate the coincidence errors resulting in particle measurements taken through the length of the aperture.

High resolution image forming optical system

Abstract: A high resolution image forming optical system provided with an annular aperture stop arranged near the front side focal plane of a condenser lens and an annular filter arranged in a position conjugate with the annular aperture stop with respect to the optical system including the condenser lens and an objective in order to improve the image-forming performance.

A new correction lens

Abstract: A new electrostatic lens capable of correcting third-order aperture aberration is proposed. The new lens is called a self-aligned quadrupole correction lens and consists of an electrostatic quadrupole and an aperture electrode. An octopole field component is automatically created within the quadrupole field by excitation of the aperture electrode. The potential distributions of this lens are calculated by successive over-relaxation techniques involving the numerical solution of Laplace's equation in three dimensions. Correction properties for all the aperture aberration coefficients are obtained by using the potential distributions. The aperture aberrations have been accurately measured by means of the shadow-image technique, and compared with those calculated using the above potential distributions. It was confirmed experimentally that the aberration in the convergent plane can be cancelled completely by the new correction method.

Enhancement of acousto-optic filter resolution using birefringence dispersion in CdS

Abstract: A CdS acousto-optic tunable filter has been constructed and operated near the band gap. The filter exhibits a large enhancement of spectral resolution that is due to birefringence dispersions. Over the wavelength range 530 to 545 nm, a half-power bandwidth of 20 A was obtained with an angular aperture of 38 degrees.

Automatically adjustable aperture stop for optical scanning system

Abstract: In an optical scanning system suitable for use in an aircraft for ground contour measurements, wherein the received image from an illuminated ground spot is reflected from a rotating prism onto paraboloidal mirrors which focus the image at a common focal point, and wherein the rotating prism is also used to transmit the scanning spot-illuminating beam, a wedge-shaped light guide accepts the coincident focused images and funnels them into a photoelectric detector. Because the prism rotates at high speed, variations in light signal transit times due to differences in target distance over the range of the scan cycle and due to differences in aircraft altitude cause the image focal point to shift, necessitating a relatively wide rectangular input aperture on the light guide, resulting in the admittance of large amounts of background light in to the detector. An adjustable shutter is positioned immediately in front of the light guide input aperture to effectively limit the size of the aperture and thereby reduce the background light interference. Shutter baffles which move in response to aircraft altitude are mechanically coupled such that they provide an aperture opening just sufficient to admit the range of image focal points for that altitude.

Mode cutoff frequencies in elliptical and large numerical aperture optical fibres

Abstract: It is shown that by perturbation of the weakly-guiding, circular fibre, it is possible to obtain, in a straightforward way, accurate information about the cutoff characteristics of the higher-order modes in optical fibres having either an elliptical cross-section (with aspect ratios as large as 2∶1) or a relatively large numerical aperture.

Inverted telephoto type wide angle objective of large relative aperture

Abstract: The wide angle objective of the inverted telephoto type with a high relative aperture. It includes from front to rear, a first lens group of negative power, a second lens group of positive power and a third lens group of positive power, well corrected for the various aberrations with predetermined conditions for the focal length of each lens group, lens form and refractive indices of the glasses of the lens elements.

Four-group great aperture ratio zoom lens

Abstract: A great aperture ratio zoom lens has, in succession from the object side, a first lens group of positive refractive power having a focusing function, a second lens group of negative refractive power having a magnification changing function, a third lens group of positive refractive power having a correcting function for keeping the image plane at a predetermined position, and a fourth lens group of positive refractive power having an imaging function. The first to third lens groups from a substantially a focal magnification changing portion. The fourth lens group includes, in succession from the object side, a forward group comprising a positive meniscus lens component having its convex surface facing the object side, a positive lens components having its surface of sharper curvature facing the image side, and a biconcave lens component, and a rearward group having a negative lens component and a positive lens component. The zoom lens satisfies certain conditions.

Tunable large angular aperture TeO 2 acousto-optic filters for use in the 1.0–1.6 μm region

Abstract: The design of tunable large angular aperture TeO2 noncollinear acousto-optic filters for use in the 1.0–1.6μm region is discussed. It is shown that it is possible to maximize the angular aperture of such a filter by the correct choice of the direction for the acoustic wave vector and that this required direction is independent of the operating wavelength in the range 1.0–1.6μm. The theoretical model adopted is verified by comparison with experimentally measured filter characteristics and the design of filters with narrow bandwidths and low power requirements is discussed.

Projection lens system

Abstract: PURPOSE:To obtain an achromatic projection lens where the aberration reaching the low order is corrected well, by combining >=3 plane Fresnel lenses to constitute the projection lens and setting radiuses of curvatures of step lenses forming respective plane Fresnel lenses to values to satisfy sine conditions CONSTITUTION:In a lens system consisting of k(>=3)-number of plane fresnel lenses 1-(k), the geometric tracing calculation for the beam going from an object point P at an angular aperture Uj is performed up to the surface of the k-th lens, and inclinations ui of beams, which are made incident to Fresnel lenses 1-(k), to the optical axis and their heights hi from the optical axis are determined successively In respect to refractive indexes of step lenses of respective Fresnel lenses, the refraction on a virtual spherical surface where a radius ri of curvature is given by a proper inter-polating expression is considered, and step lenses are handled as prisms having vertical angles phii=sin (hi/ri); and in respect to refracted beams, sine conditions of refraction are satisfied, and vertical angles phii are calculated successively up to a vertical angle phik where the refracted beam passes an image point P bar This operation is repeated to obtain an achromatic projection lens system where the aberration reaching the low order is corrected well

Electron beam welding machine - with adjustable intermediate lens reducing aperture angle for same high directivity

Abstract: Electron beam welding machine has an electron gun with a Wehnelt electrode between the cathode and the tubular anode. It produces a beam of high directivity and a large aperture angle which passes through an intermediate lens in the anode mount. This lens is set to focus the beam to a smaller divergent aperture angle and is followed by adjusting coils. The cut-off frequency for the magnetic reversal of the intermediate lens is at least 500 Hz. The high directivity results in a better weld penetration, i.e. a very deep and very narrow seam over a wide working range.

Reflex zoom lens having aperture scale

Abstract: A reflex zoom lens assembly includes a reflection optical system in which the full-aperture F number varies with focal length. A zoom ring of the assembly includes an aperture scale correlated to the focal length.

Real-Time Constant Depth Scanning with Phased Arrays

Abstract: Constant depth scanning (C-scanning) differs from B-scanning in that the imaged cross-section lies in a plane which is perpendicular to the scanning beam rather than in a plane which contains it. The potential merits of C-scanning in medicine include the ability to image cross-sections which lie parallel or nearly parallel to the body surface, e.g. coronal cross-sections of the orbit or breast, and the ability to take advantage of strong focussing since large beamwidths before or after the focal zone are irrelevant. Since the high lateral resolution, high sensitivity and large angular aperture of a strongly focussed beam are qualities which are well suited to the detection and mapping of scattered ultrasound, C -scanning is a promising mode for tissue differentiation.

Pancratic (zoom) lens

Abstract: For the purpose of achieving a focal range of between 4 and 15 mm and an aperture of at least 1:1.3, a pancratic taking lens is constructed merely from a negative and a positive lens cluster which can be mutually displaced relative to the optical axis. Due to the special relation of the focal lengths of the lens clusters provided in the negative first element, the correction state of the lens is comparable to pancratic lenses constructed from four clusters and having the same power and aperture.

Origin of Anomalous Behavior in Transducers Used in Acoustical Imaging

Abstract: Good design of the transducer arrays frequently used in acoustic imaging devices like those reported by a number of authors(1–8) is of major importance for obtaining good images after reconstruction. This proves even more crucial if one tries to get very good resolution, with a correspondingly small spatial period, say of the order of one acoustic wavelength, of the array. The major drawback of the coupling which then arises between neighbouring transducers is a narrowing of their radiation pattern. This leads in turn to a decrease of their angular aperture together with a degradation of the lateral spatial resolution of the image, or a narrowing of the scanning angle in sector scan devices like those designed by some authors (9–10).

Angular aperture compensating device of engine throttle valve

Abstract: PURPOSE:To prevent an engine speed from being reduced due to an increased load by activating an actuator to inrease an angular aperture of a throttle valve for compensation as soon as the engine is started and releasing it under a scheduled running condition. CONSTITUTION:Immediately after an engine is started, a car speed is less than 20km/h and an engin speed is 1,500rpm or less, therefore, irrespective of outer loads 32 through 35 a solenoid 20 is made on by an AND circuit 39 output causing a valve plug 21 to close a valve hole of a bulkhead 17, and only a negative pressure source 23 is introduced between diaphragms 9, 11 increasing an angular aperture of a throttle valve 4 for compensation. When the car speed reaches 20km/h or higher, an inverter 42 output and also a flipflop circuit 44 output are cut off, no output is generated from an OR circuit 37 even if at 1,500rpm or less, no output is fed from the AND circuit 39 making the solenoid 20 off, and the angular aperture compensation of the throttle valve 4 is suspended. If one or more outer loads are present while the engine speed is 1,500rpm or less, the AND circuit 39 generates an output continuing the compensation.