Showing papers on "Angular aperture published in 1968"

A three-aperture electron optical lens for producing an image of variable energy but fixed position

Abstract: An experimental study has been made of the imaging properties of a three-aperture electron-optical lens system. In general this lens has all three aperture potentials different from each other. An apparatus was constructed to determine the potential of the middle aperture required to maintain a constant image position while the potential of the last aperture (and hence of the image) is varied, the object position and potential being kept constant.

Effect of Numerical Aperture of Microscope Objectives on Film‐Thickness Determinations

Abstract: The use of high‐power magnification with large numerical aperture (N.A.) objectives in determining the thickness of transparent films requires a thickness correction due to the effective angle of incidence not being perpendicular to the substrate. The effective angle of incidence is dependent upon both the numerical aperture of the objective and the aperture diaphragm of the microscope. Under extreme conditions the uncorrected measured thickness can be as much as 10% smaller than the actual thickness. The error can be kept to less than 3% or 4% with reasonably high N.A. objectives by reducing the aperture diaphragm of the microscope. In many cases, the correction can be neglected depending on the precision required.

Periodic scan magnification for laser beam deflection

Abstract: Periodic scan enhancement takes advantage of iteration or summation of contributions from individual scanning sections. Vignetting at the scanning aperture is avoided, permitting employment of a multiplicity of elements whose sizes are diffraction limited. This is achieved by the interposition of alternate optical transfer elements that reimage the aperture of one scanning element upon the aperture of the next. The necessary progressive increase in aperture size occurs at the (static) transfer optics rather than at the (dynamic) scanning elements.

Laser Beam Scan Enhancement Through Periodic Aperture Transfer

Abstract: A new approach to laser beam scanning is introduced which is sufficiently general to be applied to a wide variety of techniques. Periodic scan enhancement is described as a method of taking advantage of iteration or summation of contributions from individual scanning sections without imposing the progressive increase in aperture size. Vignetting at the scanning aperture is avoided, permitting employment of a multiplicity of elements whose sizes are diffraction limited. This is achieved by the interposition of alternate lenticular elements which reimage the aperture of one scanning element upon the aperture of the next. Thus, the responsibility of increased aperture size as scan progresses is transferred from the (dynamic) scanning element itself to the (static) transfer optics. Several examples illustrate application of this technique. Over-all optics is considered to approach diffraction-limited performance with minimum loss.

Photographic lens of large aperture ratio having long back focus

Abstract: LENS SYSTEM OF A MODIFIED GAUSS TYPE IN WHICH THE THICKNESS OF THE SECOND LENS GROUP IS REDUCED AND THE THICKNESS OF THE THIRD GROUP IS INCREASED, AND IN WHICH THE LAST GROUP IS SEPARATED INTO TWO LENS ELEMENTS TO LENGTHEN THE BACK FOCUS OF THE SYSTEM AND PROVIDED A F:1.4 LENS CORRECTED FOR SPHERICAL AND CHROMATIC ABERRATIONS, ASTIGMATION AND COMA, WITH AN ANGULAR FIELD OF $23*.

Wide angle photographic objective of large aperture ratio

Abstract: The present invention provides a compact wide angle camera lens system of large aperture ratio having long back focus comprising eight lens groups, by which the aperture ratio of F/1.4, angle of field 62* and longer back focus than the focal length of the whole system is obtained.

Diffraction by a circular aperture in a non-planar screen

Abstract: An edge-current method is formulated for the problem of diffraction by a circular aperture formed by the envelope of a system of wedges. Some experimental results are presented for comparison. For various non-planar screens it is found that the aperture field is not changed appreciably by changes in the geometry of the screen on the image side, or by changes in the edge geometry. However, the geometry of the screen on the source side has a large influence on the aperture field.

Determination of the aperture field of an antenna by a beam-displacement measurement

Abstract: A method is given for obtaining the scalar amplitude distribution in the aperture of an antenna through the single precise measurement of the aberration of the direction of the peak of the radiated beam caused by partially obscuring the aperture by a refiectionless dielectric sheet of known small phase-insertion delay. Analysis is presented whereby the distribution obtained can be presented as the sum of presumed modes in the aperture, although the scalar treatment does not allow the phases of such modes to be assumed. Agreement with experiment is shown to be quite good for a linear aperture in the form of an Eplane sectoral horn, and extremely good for a circular antenna with a monopulse feed giving precise measurements of the angular beam displacement.

Focal-Region Fields of Annular and Sectoral Microwave Apertures*

Abstract: This paper concerns an experimental and theoretical study of the amplitude and phase structure of the image of a point source, formed by an ideal microwave-lens focusing system having its circular aperture partially obscured by disks or sectors of various sizes located in the aperture plane. The f/D ratio, the wavelength and the aperture diameter are respectively 2.7, 3.2 cm and 19.5 wavelengths. The exact Helmholtz–Kirchhoff formula is used in the numerical computations and is compared with the Rayleigh formulas.Diagrams are presented, showing measured and calculated fields and their characteristics are discussed. In the case of asymmetrical apertures, only the amplitude distribution is symmetrical in the focal plane, whereas the phase is not and both the amplitude and phase are unsymmetrical in all other regions.

The influence of screen geometry in diffraction by a circular aperture

Abstract: An edge-current theory, valid for high frequencies, is derived for the problem of electromagnetic diffraction by a circular aperture in a thin conal screen. Calculations of the axial and aperture field are compared with experimental measurements and with the Rayleigh approximations. For the angle of inclination α greater than 90° it is found that the non-planar screen geometry has little effect on the diffracted field, except for the reflection interaction. For α < 90° the fields in and near the aperture are drastically affected, but elsewhere behind the aperture the field shows little change. The edge-current theory predicts the field accurately in all cases except for the reflection interaction.

Far-field intensity distribution from a diffracting aperture in a turbulent medium

Abstract: : Given is an analysis of the effect of atmospheric turbulence in the Fraunhofer region on a near-horizontal beam of finite cross-section near the earth's surface. The far-field intensity distribution at optical frequencies of an initially plane wave from a finite, circular, source aperture is obtained as a function of range and angle for various values of the index structure constant. Describing the turbulence-induced index of refraction fluctuations by the Kolmogorov spectrum, it is found that the time average of the peak radiant intensity in the Fraunhofer region of a finite source aperture decreases with range at a much faster rate than the intensity calculated from absorption and scattering by molecules and particulate matter. Specifically, a beam from a 2- cm aperture at a wavelength of 0.6328 microns in moderate daytime turbulence will have an unscattered range of 5 km. For small values of the inner turbulence scale, the effects of turbulence are dominant over most of the ranges of interest.