The spectral response of two typical x-ray films was determined as a function of the truly absorbed energy and also as a function of the number of absorbed quanta needed to produce a given optical density. With decreasing wave-length a better utilization of the kinetic energy of the photo and recoil electrons takes place in the process of photographic image formation. The number of absorbed quanta needed to produce the same photographic effect decreases rapidly with decreasing wave-length. Correspondingly the average number of grains made developable per absorbed quantum increases. These data, together with those of the range of electrons in silver-bromide and of their energy loss per unit path-length permitted the determination of the inherent sensitivity of the average grain. Comparison between the sensitivities to visible radiation, and to x-rays, reveal great differences in efficiencies of latent image formation between films. The average grain of Non-Screen film requires the formation of 210 latent image silver atoms by photo or recoil electrons, and 105 silver atoms by exposure to blue light. The corresponding figures for High Speed x-ray film designed for medical work with calcium tungstate intensifying screens are 270 silver atoms for electrons and only 8 silver atoms for blue light. This relative inefficiency of direct x-ray exposures is predominantly due to the formation of large amounts of internal latent image.
The spectrum of argon, krypton, and xenon excited by a repetitive condenser discharge method has been studied in the near infra-red region. The use of this method of excitation and a large infra-red spectrograph using a lead sulfide detector reveals about 170 new lines in these gases. About three-fourths of the lines are classified by known terms of the normal atom.Some anomalies of spectra excited by the repetitive condenser discharge method are mentioned.
Pair comparisons were used to assess the perceptual uniformity of the Munsell value (V) and chroma (C) scales near 5Y 7.5/1 for both small (0.25-0.75) and larger (1-2) increments in V and C. We conclude that in this region perceptual linearity is retained down to steps of 0.25 V and C. Bisection experiments showed that around 10R 7/8 perceptual linearity in Munsell hue (H), V, and C was retained down to step sizes of 0.25 H, 0.10 V, and 0.25 C.
Neutral points have been found by means of a rotary mixer and Munsell papers, minimizing any dispersion of individual values by individual ocular pigmentations. Determined thus, the Illuminant C values for 39 new (post-Walls-Mathews) protanopes covered a range of 3.7 mµ with the mean at 492.3 mµ, those for 38 new deuteranopes a range of 5.8 mµ with the mean at 498.4 mµ.Illuminant D values for 13 additional protanopes covered a range of only 3.3 mµ with the mean at 490.3 mµ, those for 15 recent deuteranopes a range of only 5.1 mµ with the mean at 496.2 mµ. The intergroup gap, observed earlier by Walls and Mathews and also here with
Lines are reported belonging to Ni XVIII, Cu XIX, and Zn XX for the following transitions: 3s2S-4p 2P°, 3p2P°-4s2S, 3p 2P°-n1 d 2D (n1=4, 5), and 3d 2D-n2ƒ 2F° (n2 =4,5,6). Wavelengths, energies, and term values are given.
The optical properties of aluminum and aluminum: magnesium fluoride semitransparent coatings for multiple-beam interferometry in the ultraviolet (>1800 Å) have been measured. There is good agreement between experimental values of reflectance and transmittance and those computed on the basis of extrapolated optical constants of aluminum. The effects of evaporation conditions, including rate of evaporation and the content and pressure of the residual atmosphere, on optical properties are discussed and the performance of these coatings for interferometry is summarized.
Studies were made of the visual functions of subjects with complete and incomplete achromatopsia, with particular emphasis on measurements of the rates of dark adaptation in a parafoveal region of the retina and at the fovea. When adequate preadaptation to a high luminance is achieved, the dark-adaptation curves reveal the presence of some form of photopic receptors in addition to the normal scotopic rods. Both types of receptor are present, not only in the paracentral retina, but also at the fovea.
The "Color Aptitude Test" sponsored by the Inter-Society Color Council is now a well-developed, color-matching test consisting of saturation series of carefully prepared chips in four colors. Colorimetric and spectrophotometric specifications have been presented. Analysis of some 1000 testings indicates (1) a satisfactory regularity of spacing of the chips, (2) a near normal distribution of total scores derived from weighted scores per "match," (3) good test-retest reliability consistent with high sensitivity of discrimination, and (4) a measure of reliability of individual performances in terms of test to retest change in score.
An angular interpretation of the CIE 1960 (u,υ) system is presented. This new development of the CIE 1964 (u,υ) (U*, V*, W*) system results in improved chromaticness-difference predictions and is more in accord with empirical constant-hue loci than the U*, V*, W* system.
Cummunication to Editor reports comparison of series of dirrerent blue tristimulus filters to find best representation of visual observations on textile swatches; study suggests CIE 1964 supplementary standard colorimetric observer was better than two other proposed observers.
The adjustable parameters in a MacAdam-modified version of Friele’s 1965 proposal for calculating color differences have been optimized, according to a criterion of MacAdam, to fit PGN experimental data. The mean-square error of fitting is 0.030. The distribution of the resulting color-metric coefficients more closely approximates those of the PGN data than do previous versions of Friele's proposals. The optimized primaries have chromaticity coordinates of x=0.74054, y= 0. 2 5946 for the red; x= -1.11696, y=2.11696 for the green; and x=0.13939, y= -0.03454 for the blue primary.
In response to general request of CIE Technical Committee TC 1.3 for evaluation of the proposed small-color-difference formula, tentative CIE 1976 L a b, unit color-difference contours generated this formula have been calculated and compared to cross sections in the chromaticity diagram of ellipsoids fitted nearly optimally to relevant visual color-tolerance data.
R. C. VEHSE, E. T. ARAKAWA, and J. L. STANFORD, "Normal-Incidence Reflectance of Aluminum Films in the Wavelength Region 800–2000 Å*," J. Opt. Soc. Am. 57, 551-552 (1967)
Data are presented on the wavelengths of 97 lines of 208Po and on the hyperfine structure of 31 lines of 209Po. From these data, relative values of 26 energy levels of 208Po I have been deduced. The hyperfinestructure splittings of 14 of these levels in 209Po have been determined. Some tentative identifications of the levels have been made, based on a determination of the absolute value of the fundamental level 6p4 3P2′ by application of a Ritz formula to three levels taken as 6p3(4S)np5P3′, n=7,8,9. The ionization potential of 208Po has been tentatively estimated as 8.414 V. From the measured splittings of the energy levels of the configuration 6p4 of 209Po I, the nuclear magnetic moment of 209Po is estimated to be 0.76 nm. Mrozowski’s identifications of some lines of Po I are examined. It is found that his identifications of the 4611 Å and 5940 Å lines are confirmed by coincidence of frequencies and by hyperfine-structure patterns, but that his identifications of the other lines and his determination of 6p41S0′ could not be confirmed by the data of this investigation.
Directional sensitivity of the retina (the Stiles-Crawford function of the first kind) was measured at a point 35 degrees from fixation and at the point of fixation. Three normal observers were used. The peripheral test point intercepted the retina between the optic nerve head and the ora serrata. At both test points, photopic and scotopic (one subject) Stiles-Crawford function peaks were contained within the pupillary bound and approximated the center of the pupil. Directionality at the two points was rather similar. These findings add strength to the argument that retinal receptors align approximately with the center of the exit pupil of the eye. Evidence for stability in Stiles-Crawford peak location in time is also presented.
The fine structure of the (4S°)3p3P term of O I has been determined by interferometric measurement of three triplets at 8446A, 7245A, and 6046A. The term is found to be partially inverted in agreement with Edlén’s findings.
Color discrimination functions for three observers were plotted in the short-wavelength region of the spectrum. The method of constant stimulus differences was used. Comparisons between the present results and earlier results are reported. Sensitivity proved more variable in this region than elsewhere in the spectrum.
The study reports the experimental determination of just noticeable differences in color as dependent upon wavelength at 10-mµ steps from 510 to 630 mµ. The method of constant-stimulus differences was used to produce limens in terms of measures both of central tendency and of dispersion of judgments. The data have been analyzed to determine the different functional relationships between various colors and wavelengths. Peak sensitivity was found in the yellow region of the spectrum. The results were discussed in terms of methodological differences between the present and earlier studies and were applied to psychologically unique colors.
RICHARD WALES and R. RANDOLPH BLAKE, "Rule for Obtaining 75% Threshold with the Staircase Method," J. Opt. Soc. Am. 60, 284_1-285 (1970)
It is now wvell established in principle that superresolving optical systems can be made. Such systems, when viewing objects of finite extent, can resolve detail finer than the normal diffraction limit. This has obvious attractions for microscopy, but we may wonder whether the ultimate diffraction limit for a lens of large numerical aperture, the limit which counts in microscopy, can be beaten. Can detail smaller than one half the wavelength of light really be made visible? It can be, but only in specialized and probably limited applications.
The effects of aberrations on images formed by a total system, including the eye, are assessed in terms of modulation threshold, grating detectability, and modulation transfer functions. The effects of approximately one and two waves of third-order spherical aberration, coma, and astigmatism on the total system modulation transfer function are investigated using three-bar resolution targets and Ronchi rulings in two separate psychophysical experiments. The results of both experiments indicate that the experimentally determined system modulation transfer function is closely approximated by the theoretically calculated modulation transfer function of the total system optics (dioptrics included) in the presence of instrument aberrations. The data indicate that the eye accomodates of a "best focus" when spherical aberration and astigmatism (but not coma) are present in the instrument. The quantitative data are used to determine aberration tolerances for instruments that are designed for specific visual tasks and that employ simple targets similar to those investigated.
The size of the blur circle due to chromatic aberration in daylight is calculated. The spectral transmittance necessary to reduce the resultant penumbra to a threshold level is computed. The characteristics of such an ideal filter are similar to the transmittance of the macular pigment found in the human eye.
An optical system is called symmetric if it possesses an axis of symmetry A and a plane of symmetry containing A. A system K will be called semi-symmetric if it is merely axially symmetric, i.e., if it possesses a screw sense pointing along A. Previous work concerning the consequences of reversibility of symmetric systems is extended to the semi-symmetric case, a “reversal” of K being understood to be its rotation through 180° about a line through A and normal to it, together with a reversal of its screw-sense. It is shown that among the n(n+2) aberration coefficients of order 2n-1 there exist altogether ½ (n-1) (n+2) relations. These divide themselves into a set of relations, previously obtained in the symmetric case, between the “proper coefficients” alone, and a new set of homogeneous relations between the “skew coefficients” alone. The third- and fifth-order relations are exhibited explicitly, and some special points relating to all orders are considered. As a contribution towards a proper appreciation of the meaning of the results obtained, a fairly detailed discussion is included of the geometrical significance of the various types of aberrations possessed by semi-symmetric systems. This part of the work has been shorn of all irrelevancies and it is essentially an extension of Steward’s elegant presentation.
DOUGLAS C. SINCLAIR, "Demonstration of Chromatic Aberration in the Eye Using Coherent Light," J. Opt. Soc. Am. 55, 575-576 (1965)
M. J. KOOMEN, R. SCOLNIK, and R. TOUSEY, "Spherical Aberration of the Eye and the Choice of Axis," J. Opt. Soc. Am. 46, 903-904 (1956)
In the production of 60-inch anti-aircraft searchlight reflectors by the electroforming process, convex parabolic forms are used as molds. To avoid production of reflectors with excessive spherical aberration, it is necessary to know the inherent spherical aberration of each mold. To obtain this information, an apparatus has been devised to measure the spherical aberrations of the convex surface of a para-boloid of revolution. The optical system of the apparatus consists essentially of a collimator, a plane mirror, and a photographic plate used in the following manner. A narrow beam of light parallel to the optical axis of the mold to be tested is projected from the collimator onto a designated spot of a particular zone on the mold which is in a horizontal position. The beam of light is reflected from the mold as if it were coming from the virtual focus for the designated spot. The reflected light strikes the plane mirror, vertically placed in a predetermined position and is re-reflected so that the beam of light intersects the optical axis of the mold at a distance above the mold equal to the focal length for the designated spot in the mold being examined. The photographic plate is placed horizontally at a distance above the mold equal to the nominal focal length of the mold. The beam of light intercepts the photographic plate and produces a specified image. Eight such images are photographed on one plate at equally spaced intervals around the periphery of the zone being tested. A required number of zones are tested. Simple interpretation of the photographs yield the amount of aberration present. An important feature of this apparatus is that the interpretations of the photographs are identical to those obtained for testing concave parabolic reflectors. This apparatus aids reflector production in that it determines the abberation characteristics of the convex mold directly, thus eliminating the previous practice of making a reflector from a mold to determine the mold’s accuracy indirectly.
The spherical aberration of the eye was measured by placing a series of centered annular apertures over the eye pupil, and determining the optimum spectacle correction for each aperture. A “double star” was used as a test object. Accommodation was controlled by reflecting a second test object into the field of view. The three eyes examined had positive (undercorrected) spherical aberration when unaccommodated; in one case 2 diopters at the pupil margin. The aberration was reduced with increasing accommodation and in one case became negative at high accommodation. Homatropine reduced the spherical aberration of two of the three eyes examined. A historical review of previous work is given.
Schmidt and Maksutov catadioptric systems suffer from sphero-chromatic aberrations that are of opposite sign. By the use of a hybrid system, whose corrector is a deep meniscus lens with an aspheric curve on the external surface, the sphero-chromatic residuals have been reduced and, as a consequence, usable relative apertures have been increased.
A. IVANOFF, "On the Influence of Accommodation on Spherical Aberration in the Human Eye, an Attempt to Interpret Night Myopia," J. Opt. Soc. Am. 37, 730-731 (1947)
The loss in resolving power caused by mixtures of, and by pure primary astigmatism, coma, and spherical aberration has been studied for telescopic systems. Resolution measurements were made by use of Foucault [“Memoire sur la construction des telescopes en verre argente,” Annales de l’observatoire imperial de Paris 5, 217 (1858)] test objects of various inherent brightness contrasts. Results of these measurements were analyzed in terms of the magnitude of the aberrations expressed in terms of the Rayleigh [“Investigations in optics, with special reference to the spectroscope,” Phil. Mag. 8, 411 (1879)] limit appropriate to the best visual focus for the telescopic systems under consideration. For high contrast test objects the loss in resolution was found to be of the order of five percent per Rayleigh limit and different for each aberration. The loss per Rayleigh limit was found to be greatest for astigmatism and least for coma. On a percentage basis, the loss in resolution caused by a given aberration was found to be greater for test objects of low contrast than for those of high contrast.
The influence of the corneal shape on the quality of the retinal image has been studied. We have distinguished between the role of the cornea and that of the crystalline lens; the wave surface behind the cornea was determined. First, the corneal topology was measured by photographic keratometry. Then, for the same subject, the spherical aberration of the eye was determined by the Foucault knife-edge test. The shapes of the anterior and posterior surfaces of the crystalline lens have been determined from experimental data.
Studies that relate accommodation to axial chromatic aberration of the eye have been concerned both with quantitative changes associated with accommodation and with the variation of wavelength in focus as the eye accommodates. The experiment described uses an achromatizing lens designed to eliminate the chromatic aberration of the eye while the effect of accommodation is evaluated. Of concern is the possibility of observing the calculated slight increase of chromatic aberration with accommodation in a situation in which the chromatic aberration of the unaccommodated eye is minimized. Also of interest is the possible shift with accommodation of the wavelength in retinal focus.
If the glasses constituting a symmetric optical system are inhomogeneous, any chromatic paraxial-aberration coefficient can be expressed as a sum of the usual surface contributions, together with a sum of integrals over each inhomogeneous medium. The explicit form of the various contributions to the chromatic paraxialaberration coefficients of the first and second chromatic degree are written down. Given the dependence of the refractive index on both wavelength and position, these formulas can be used to compute the chromatic paraxial-aberration coefficients. The effectiveness of the inhomogeneities as additional degrees of freedom for the control of chromatic aberrations is discussed. Some recent work on the dispersion of glasses is reported. This work supports the use of Buchdahl’s dispersion formula and color coordinate ω in the context of the chromatic aberrations of systems operating in the visible part of the spectrum.
We have designed an aberroscope that differs from Tscherning’s classical instrument in that it makes use of an artificial astigmatism rather than an artificial myopia to defocus the image of a point source of light. A subject views the source through a ±5 D crossed cylinder lens with axes at 45° to the principal axes of an intercalated grid and sees a shadow image of the grid. The distortions of this grid image are quantitatively related to the wave aberration of the eye. Using this device we have obtained drawings for more than 50 subjects. These drawings of the grid pattern have been analyzed by means of a two-dimensional polynomial curve fitting technique that computes Taylor polynomial terms to the fourth order. From the Taylor coefficients it is possible to reconstruct the wave aberration surface. Examination of the Taylor terms so obtained shows that the monochromatic aberrations of the eye are dominated by third-order Taylor terms within the range of physiological pupil sizes, and that spherical aberration frequently appears predominantly about one axis only, a condition that we have termed “cylindrical” aberration. We have computed the optical MTF of our subjects’ eyes and find that the role of aberrations in degrading the MTF may be greater than generally believed.
The patient of this study is a protanope who is afflicted with retinitis pigmentosa. As with other patients studied, an abnormality in Stiles’s pi-1 mechanism was found in the patient’s worse eye (20/35 visual acuity). From his rejection of monochromatic color matches, we inferred that the sensitivity of the short-wave cones is reduced, but their signals are not abnormally attenuated by the middle-wave cones. The patient’s pi-4 thresholds, however, were within the range of normal control values.