Showing papers in "Journal of the Optical Society of America in 1958"

Research into the dynamic nature of the human fovea-cortex systems with intermittent and modulated light. I. Attenuation characteristics with white and colored light.

Abstract: A generally known method for the dynamic investigation of any linear system is recalled to mind. Applied to the visual organ with sinusoidally modulated light, the dynamic nature of the system fovea→brightness perception is embodied in attenuation characteristics, by plotting the ratio output amplitude over input amplitude against frequency at constant mean luminance. This manner of investigation, first applied in previous papers with white light, is expanded over a greater part of the range of cone vision and is continued with colored light. The existing theories on flicker fusion provide no explanation for the shape of the attenuation characteristics obtained with the experiments and calculated from investigations of other authors.

Photoelectric Color Difference Meter

Abstract: The color difference meter has three photodetectors, each with a separate tristimulus filter, and each receiving some of the light reflected from the specimen Signals from the photodetectors are measured by analog circuits that give rectangular coordinates for surface colors in close correspondence to their positions in uniform color space The first model described in 1948 uses barrier-layer photocells and three tristimulus filters Recently, a model employing vacuum phototubes and four filters has been built Use of vacuum phototubes makes it possible to substitute a dc amplifier and pivot meter for the suspension galvanometer necessary with barrier-layer photocells By thermostatting the phototube chamber, excellent stability is obtained A light pipe in the viewing beam provides a more stable and efficient mixer of light to the different photodetectors than the white-lined sphere used previously

Contour Perception, Illusion and Reality*

Abstract: A qualitative analysis of the perception of contours indicates that, to counteract the filtering characteristics of the eye, there may be a process of contour enhancement by a second difference correction. By simple experiments, contours corresponding to true edges, contours perceived although there are no edges in the external intensity distribution, and certain aspects of contrast are investigated with results that show agreement with such a process.

Models for Spectral Band Absorption

Abstract: An exhaustive, theoretical study is made of the various models that have been proposed to represent band absorption. These models are compared with each other; a derivation is given of the regions where they predict the same absorption. The regions of validity for various useful approximations to these models are also given. The statistical model is extended to include the random superposition of a finite number of Elsasser bands. Thus a continuous spectrum of absorption curves is obtained between the results for the Elsasser and the pure statistical models. The absorption predicted by the statistical model when there is a specific number of spectral lines in the frequency interval under consideration is compared with the limit as the number of lines approaches infinity. It is shown that the shape of the absorption curve obtained from the statistical model is independent of the distribution of line intensities in the band for most cases of interest. The absorption from the statistical model including the effects of overlapping is shown to depend only on an average equivalent width for a single line. This result is used to derive the band absorption for the statistical model with Lorentz, Doppler, and other line shapes.

Research into the dynamic nature of the human fovea-cortex systems with intermittent and modulated light. II. Phase shift in brithtness and delay in color perception.

Abstract: In this paper it is shown that the well-known residual brightness flicker just above the color-flicker limit with heterochrome flicker photometery can be brought down to zero by introducing an external phase correction in one of two light beams sinusoidally modulated 100% in antiphase and simultaneously presented to the eye. The phase correction is found to be a function of luminance, color difference, and frequency.From the attenuation characteristic of the color system it is found that the extra delay in color perception at 595 mμ is caused by a single integration process with a time constant of about 120 msec at high luminance; at low luminance a triple integration process occurs with the same time constant.

Refractive Index of Arsenic Trisulfide

Abstract: The refractive index of a sample of As2S3 was determined at three temperatures near 19°, 25°, and 31°C for selected wavelengths in the range 0.57 μ to 11.8 μ. A five term Sellmeier type dispersion equation was fitted to the averaged data reduced to 25°C; four of the constants were chosen to approximate an absorption continuum in the ultraviolet and visible while the fifth term was arbitrarily chosen as beyond the infrared absorption edge. The indexes of refraction in the visible region of two other samples were obtained for comparison.

Study of visual acuity during the ocular pursuit of moving test objects. I. Introduction.

Abstract: Visual acuity may be measured during the voluntary ocular pursuit of moving test objects. This visual function has been referred to as dynamic visual acuity. The apparent movement of the test object is produced by rotating a mirror in the desired plane of pursuit by means of a wheel and disk type variable speed drive. The range of angular velocities utilized is 10°/ to 170°/sec at the nodal point of the tested eye. It is shown that visual acuity deteriorates markedly and significantly as the angular velocity of the test object is increased. It is shown further that the relationship between visual acuity and the angular velocity of the test object may be described satisfactorily by the semiempirical equation Y=a+bx3. It also is pointed out that individuals possessing similar static acuity may differ significantly in their dynamic acuity. The possible causes for the observed deterioration of acuity are discussed and it is concluded that imperfect pursuit movements of the eye result in a continued motion of the image on the retina. This motion results in reduced intensity contrast, which is a factor in producing loss in acuity.

Solc Birefringent Filter

Abstract: A new birefringent filter composed of a series of retardation plates between a single pair of polarizers has been described by Solc. The filter is analyzed and compared with the Lyot filter. It is found that the Solc filter is inferior to the Lyot filter in the suppression of parasitic light in secondary maxima near the primary transmission bands, although its band width is slightly less, and its transparency is very much better if both filters use Polaroid film for polarizers.

Continuous Emission Spectra of Rare Gases in the Vacuum Ultraviolet Region. II. Neon and Helium

Abstract: The experimental conditions for, and the characteristics and origin of the recently found Ne continuum are described. The 600 A band and the continuum of helium were reinvestigated in relation to the diffuse bands and continua of the other rare gases. It is suggested that both probably originate from the transition A1∑u+−X1∑g+ of He2, because of the similarity of their characteristics to those of the resonance lines and continua of the other rare gases, Ne included.

Design of Multilayer Filters by Considering Two Effective Interfaces

Abstract: Any nonabsorbing multilayer system may be completely described by two effective interfaces. An analysis based on this representation is applied to deduce the properties of systems consisting of one or two half-wave layers surrounded by reflecting stacks. The salient features of the transmission characteristics are easily obtained. The conditions to be fulfilled in the design of band-pass filters of various band widths and of low-(frequency) pass filters are deduced. It is shown that double half-wave systems have theoretical advantages in band shape and peak transmission over single half-wave systems. This is confirmed experimentally.

Basis for judgments of relative brightness.

Abstract: The hypothesis is offered that relative brightness judgments are based upon experience with the way the amount of light reflected by objects changes with their distance from the light source.The experimental results support this hypothesis. One group of 40 subjects judged half brightness, and another 40 estimated the change in luminance corresponding to moving a hidden point light source to twice the distance from an illuminated standard field. Judgments of the two groups were equivalent.Under stimulus conditions designed to represent the common visual situation (stimuli subtending wide visual angles, adaptation approximating stimulus levels), one quarter the standard luminance was correctly chosen for the effect of doubling distance from the source, and the same fraction was chosen for half brightness for all standard intensities (0.00086 to 87 millilamberts).Under less familiar conditions similar to those employed for the bril scale (small stimuli with black backgrounds, indeterminate levels of adaptation) half brightness judgments were again equivalent to estimates of the effect of doubling distance from object to light source. These estimates were less than one-quarter standard luminance.The hypothesis is discussed in terms of sensory scaling in general, and the neutral value and bril scales in particular.

Eye fixations recorded on changing visual scenes by the television eye-marker.

Abstract: By the use of television techniques it is possible to record the position of a man’s gaze upon a picture of the scene at which he is looking. The corneal reflection of a light is picked up by a television camera, which magnifies the movement of the spot about 100 times. The scene at which the man is gazing is provided by a second television camera, and the corneal reflection is superimposed upon another television monitor also showing the same scene. By suitable calibration, this spot can be made to lie upon that part of the scene being regarded and the accuracy with which this can be done is within one or two degrees.Thus it is possible to see where a man is looking at any moment, and simultaneously to record the composite eye-scene picture by means of a motion picture camera. In addition to its practical uses, this method is particularly useful for answering such general questions as whether a subject always sees what he is directly looking at, what kind of cues catch his attention when he is searching, and what sort of changes in a display catch his attention. It is primarily intended for use with a moving display, as it records the point of view directly on to each state of the display. Successive glances therefore indicate the order in which particular parts of complex displays are selected, as well as the exact moment at which the gaze changes to a new position.

Design of Multilayer Filters by Successive Approximations

Abstract: A relaxation method is used to adjust the thicknesses of the films of a multilayer in order to alter its transmission characteristics in a limited spectral region. This method is used to modify the spectral transmission of a short-wavelength pass multilayer and a broad-band dielectric mirror. The computations also furnish information useful in controlling the thicknesses of the layers in the fabrication of a multilayer.

Variability of Accommodation during Steady Fixation at Various Levels of Illuminance

Abstract: Using the stigmatoscope, the variability of the dioptric power of the eye during steady fixation was measured for four observers over a range of intensities from 2¯.5 to 3.0 log trolands in one-half logarithmic steps. Two different viewing conditions, (constant and variable size test letters), were studied but no significant difference between them was obtained. There was almost a fourfold decrease in the variability of the settings as the intensity was increased over this range. There was a sharp transition at one troland, suggestive of a discontinuity between scotopic and photopic vision. These changes could be eliminated by cycloplegia of the fixating eye. Essentially the same results were obtained when the refraction of one eye was measured objectively (with a concidence optometer), while the other eye fixated the chart. This latter technique is, however, less valid at the lower intensities because of the tendency to fixate the measuring light of the optometer. The data can be quantitatively described by a theory which postulates that the accommodation is continually fluctuating and that the limits of fluctuation are proportional to threshold ΔI/I.

Wavelength discrimination for point sources.

Abstract: Wavelength discrimination curves have been measured for two normal trichromats for three field sizes and various intensities. In order to obtain high-intensity levels in the blue region, a high-pressure xenon arc was used as a source. Results for the 1° field agree essentially with those of previous workers. The higher blue intensities have led to the establishment of a definite minimum at 420 mμ. Results for the smaller field sizes differ considerably from previous data. The chief reason for this seems to he in the viewing technique used. While previous authors employed strict fixation, this paper reports data obtained with a scanning technique. The effect of different methods of plotting is briefly discussed.

Optical properties and structure of cerium dioxide films

Abstract: The refractive index n and the absorption coefficient k of evaporated CeO2 films were measured in the wavelength region from 0.22 μ to 1.0 μ. Films produced by direct evaporation of CeO2 were found to be extremely durable and nonabsorbing in the visible and can be used as beam splitters and as high-index films in multilayer film combinations. The refractive index of CeO2 films depends strongly on the temperature of the substrate. An increase of the substrate temperature from 25°C to 300°C increases the refractive index of the condensed film material at λ=550 mμ, from about 2.2 to 2.4. The absorption of CeO2 films increases strongly below 400 mμ and reaches a maximum at 300 mμ. Evaporated CeO2 films show the same cubic structure as compact material and crystallize without preferred orientation on amorphous substrates. The crystal size in the condensed films increases with increasing temperature.

Study of Light Deviation Errors in Triple Mirrors and Tetrahedral Prisms

Abstract: In this study, a procedure based upon vector analysis methods is outlined for the tracing of optical rays through triple-mirror and tetrahedral prism retrodirective reflectors. This procedure is utilized to determine the light deviation errors of such reflectors in terms of the errors in the three dihedral angles between the reflecting surfaces. It is shown that if the dihedral angles of a given reflector are in error by a tolerance amount ±θ, the resulting deviation errors of that reflector will not exceed 3.26θ for a triple mirror or 3.26 Nθ for a tetrahedral prism of refractive index N.Experimental verifications of the theoretical relationships developed in this study are described. The procedures which are used in this verification are applicable to “in-process” and final inspection operations during the manufacture of prismatic retrodirective reflectors of moderate precision.

Cube-Root Color Coordinate System

Abstract: A visually uniform color coordinate system, based upon simple mathematical formulas, is described. This system resembles the Adams chromatic-value system but replaces the quintic-parabola function with a cube-root function. For colors having reflectances greater than 0.5% the color spacing obtained agrees with Munsell spacing as closely as the modified Adams system. At lower reflectances an expanded color spacing over that of the Munsell system is provided. The cube-root equations can be solved directly for color coordinate differences in terms of simple functions of the difference in colorimeter readings or tristimulus values. The computation of color coordinates in this system is simpler and requires less computational precision than other visually uniform color coordinate systems. A simple slide rule for computing color differences in cube-root color coordinates is described. A modification of the cube-root color coordinate system which provides nearly perfect representation of the spacing of Munsell colors is described, and the appropriateness of the assumptions required to obtain this behavior is discussed.

Comparison of Scotopic, Mesopic, and Photopic Spectral Sensitivity Curves

Abstract: Spectral sensitivity curves have been established for the ten-degree periphery throughout a range of intensities from absolute scotopic threshold to a level five log units above threshold. Surround conditions included adaptation of the eye both to complete darkness and to the light level under investigation. In addition, foveal curves have been established at one level under the same experimental conditions as the peripheral curves.The results show that there is no large shift in the curves toward the longer wavelengths with increasing intensity until a level five log units above threshold has been reached, and that, even at this point, the peripheral curve does not approach the spectral sensitivity found in the foveal curve. While the curves retain the predominant scotopic element, that is, sensitivity to the shorter wavelengths remains basically unchanged, sensitivity to the longer wavelengths does increase throughout the entire range of intensities investigated. This is true for both surround conditions; in addition, a slight increase in sensitivity to the long wavelengths and better brightness discrimination are found with the lighted surround.

Analysis of experiments in binocular space perception.

Abstract: Experiments connected with Luneburg theory as developed by the author are analyzed with the purpose of making explicit their underlying assumptions. In particular, the role of ad hoc assumptions is explored in detail and minimized wherever possible. It is shown that the special assumptions under which much of the experimental work was executed may be considerably broadened thereby indicating how the theory may be more directly founded upon experiment. The principal problem is the determination of the sensory visual transformation between the geometry of the binocular perception and that of the stimulus, and, in particular, the determination of the visual radial distance function. Three principal techniques, the double circumhoropters, the Blumenfeld alleys, and the equipartitioned geodesics are discussed from this generalized point of view. The specific experimental material treated here consists of results obtained by Zajaczkowska, Shipley, and the Knapp Laboratory group at Columbia University. Some of these results appear for the first time. Theoretical material presented for the first time consists most notably of the analysis of the equipartitioned geodesics, the two-point experiments for the determination of Gaussian curvature, and the meta-theoretical discussions of the several experiments.

Far Infrared Spectrograph for Use from the Prism Spectral Region to about 1-mm Wavelength

Abstract: A far infrared spectrograph is described. The mounting is of the Czerny-Turner type. The radiation sources are a heated platinum strip used in the short-wave region and a high-pressure mercury lamp used in the long-wave region. Golay cells with diamond or quartz windows are used as detectors. Holders for filters to eliminate short-wave radiation and for reflection or transmission samples are designed for convenient use. Special chambers provide optical paths for long gas cells and provide holders for small solid samples. All parts of the optical system are in a vacuum tank and are remote-controlled. Spectra are automatically recorded on a strip-chart recorder. Spectra in the region from 18 microns to about 1 mm, obtained with six echelette gratings, are shown.Reproducibility of wavelength settings is one part in 5000. Resolution of better than 0.5 cm−1 throughout the entire spectral region has been achieved.

Study of visual acuity during the ocular pursuit of moving test objects. II. Effects of direction of movement, relative movement, and illumination

Abstract: It was demonstrated that the manner in which visual acuity deteriorates as the angular velocity of the test object increases is similar regardless of whether the motion is produced by moving the target vertically, horizontally, or by rotating the observer in a horizontal plane. It was shown also that the semiempirical equation Y=a+bx3 describes satisfactorily these three types of movement. It was pointed out that individuals having a low acuity threshold in the vertical plane of movement will be likely also to have a low threshold in the horizontal plane. It was shown that although 5 to 10 footcandles may be sufficient illumination when the test object is stationary, visual acuity is substantially benefitted by increases up to 125 footcandles when the observer is rotated. This corroborates earlier findings reported by Ludvigh.

Some Optical, Thermo-Optical, and Piezo-Optical Properties of Synthetic Sapphire*

Abstract: Measurements of the ordinary and extraordinary refractive indexes of synthetic sapphire are reported Direct independent measurements of the birefringence are given Temperature and piezo-optical coefficients of birefringence are given and combined with published data and calculations of W L Bragg to yield order of magnitude values for the thermal coefficient of expansion and Young’s modulus

Evaluation of Metameric Colors

Abstract: A method is described which allows a quick evaluation of a large number of spectral reflectance (transmittance) curves which with respect to a given light source and the 1931 CIE standard observer produce metameric colors The method is based on a precalculated set of linearly independent metameric blacks and demonstrated by a numerical example

Axiomatics of binocular vision; the foundations of metric geometry in relation to space perception.

Abstract: The theory of binocular vision is given a foundation in the empirically defined relations of length ordering and alignment. The development differs significantly from earlier presentations in not requiring the presupposition of numerical metric relations, but shows instead how quantitative metric properties may be derived from the most elemental nonquantitative observations of visual experience. The requirement that the axioms reflect direct visual experience results in a development of the foundations of metric geometry which is unconventional in that topological assumptions and assumptions as to the prolongation of segments are proscribed.

On the Point and Line Spread Functions of Photographic Images

Abstract: The paper describes the three basic functions used to describe the image forming properties of photographic materials. The functions are the line spread function, the point spread function, and the transfer function (spatial frequency response). Only one of the three functions is independent, and therefore three pairs of conjugate relations exist among them. All six relations are given explicitly.The relations are exemplified by deriving the point and line spread functions of Super-XX, Kodachrome, and Microfile film from the transfer function measurements of Schade. The results are given in Figs. 2 and 3. Four different characteristic lengths associated with the spread functions are defined, and their numerical values are given in Table I.

Summated response of the retina to light entering different parts of the pupil.

Abstract: Contradictory additivity data of previous investigators, defined as the summated response of the retina to light entering different parts of the pupil, have led to an intensive study of variables inherent in these measurements. The experimental results have demonstrated that the Maxwellian and the ordinary type of viewing may be used interchangeably in Stiles-Crawford and additivity effect experiments. The experiments conducted in this research have revealed that additivity data are affected by at least the following two factors: the Stiles-Crawford effect and the blur of the retinal image. When blur is eliminated in additivity studies, the Stiles-Crawford effect does not reduce perceived brightness as much as might be predicted. The blur effect, caused by ocular aberrations, spherical and chromatic aberrations in particular, is a variable dependent upon the observer. This variability is thought to account for the several discrepancies in the data found in the literature. Experiments concerning the effect of blur on perceived brightness have been completed. It was shown that blur reduces perceived brightness of a field, and the degree of the reduction is dependent upon the test method.

Far infrared transmission through metal light pipes

Abstract: The fractional transmission of far infrared radiation through metal light pipes is calculated and compared with experimental data. Transmission factors greater than fifty percent are obtained over distances of several feet with typical parameters. Condensing cones allow the output radiation to be concentrated onto a small detector area for spectroscopic applications.

Behavior of Lead Sulfide Photocells in the Ultraviolet

Abstract: Spectral response measurements have been made on Eastman Kodak lead sulfide cells in the wavelength range 0.2–2.0 μ. The quantum sensitivity (defined as the number of electronic charges passed in the external circuit per incident photon) is roughly constant for wavelengths greater than 0.6 μ, but rises linearly with photon energy at shorter wavelengths. The increase in quantum yield is attributed to electron multiplication by secondary internal emission.