Disc Sector Research Articles

New Sector-Disk Method for Comparing Light Intensities

A method of using two rotating sector disks to attenuate a beam of light by an exact integral factor is described. The method provides a means for measuring intensity ratios or filter transmissions without errors due to detector nonlinearity, provided that the detector obeys Talbot's law, and has a number of advantages over the ordinary sector-disk method used for this purpose. An apparatus for testing whether the detector obeys Talbot's law is also described.

25] Steady-state relaxation spectrophotometry

This chapter discusses the mechanism of steady-state relaxation spectrophotometry. The design of a spectrophotometric system is concerned with maximizing the information-to-noise ratio, by increasing the information, minimizing misinformation, and minimizing noise. In steady-state relaxation of sinusoidally driven systems, the photosynthetic apparatus is driven by actinic light, which is modulated to give 50% on and 50% off time of variable frequency. The wave form of the actinic light is preferably sinusoidal. This forces the electron carriers to respond in a sinusoidal response at the frequency of the actinic light. The amplitude and phase relationship of the carrier's response is governed by the appropriate kinetic parameters. It allows noise reduction through extreme narrow banding. The main parts in the spectrophotometer instrument includes (1) a source of monochromatic light and suitable detecting system, (2) a source of strong modulated actinic light, and (3) a rotating sector disk which causes the sample to be alternately illuminated by the measuring and actinic lights.

An accurate sputtered spot pattern monitor

An apparatus is described which enables the formation of sputtered spot patterns to be continuously monitored and photographed. Provision is also made to enable the single crystal target to be rotated and tilted to present any orientation to the incident ion beam. The target crystal temperature can be varied from liquid nitrogen temperature to several hundred degrees. The equipment has been used to study the temperature and incident ion energy variation of sputtered spot patterns from gold single crystals. The photographic records of the developing spot pattern are measured by microdensitometry. The microdensitometer is calibrated with a standardizing sector disk using thin films of gold whose thickness is measured by high resolution multiple beam interferometry.

Effect of Wavelength on the Relationship between Critical Flicker Frequency and Intensity in Foveal Vision*

The precise effect of wavelength on the judgment of critical flicker frequency (CFF) has been a controversial issue for a number of years. Some studies report no effect of wavelength; other studies indicate that wavelength is a basic determiner of the CFF threshold. The purpose of this study was to attempt a resolution of the controversy by means of a systematic and thorough investigation of the problem. The apparatus used was the Fordham calorimeter. By means of monochromators it was possible to deliver various spectral colors with a constant passband of 10 mμ to the subject. The intensity of the light source was controlled by means of neutral tint filters and an optical wedge. Flicker was produced by intercepting the beam of light with a sector disk driven by a Graham variable-speed motor. Eight wavelengths covering most of the range of the visible spectrum were used, and CFF thresholds were obtained at seven different luminance levels in eight experimental sessions for each wavelength. Three subjects with normal color vision were employed.The results showed that the wavelength of the stimulating light changes the slope of the curve relating CFF to log I. The curves at the blue end of the visible spectrum are steeper than those at the red end. Furthermore, the greater the separation between wavelengths, the greater is the probability of a significant difference between slope values. The fact that the slopes of the curves differed with wavelength does not mean that the Ferry–Porter law is invalid, but rather that one should adjust the “constants” of the equation for the particular wavelength being used. Consequently, it can be stated that CFF is a function of the wavelength of the stimulating light. The most explicit interpretation that could be made was that this change reflected some sort of change in the receptor system of the eye.

Special type of grating, possessing the properties of a neutral filter for use in homochromatic photometry

A transmission grating having wedge-shaped opaque and transparent elements is described. It is shown that it has the properties of a truly neutral filter and can be used in homochromatic photometry in the place of a rotating sector disk which is difficult to operate. This new optical device may be particularly helpful when it is desired to change the intensity of a beam of light by very small amounts. It may also find useful application in absorption spectroscopy.

Studies on the Inorganic Constituents in Biological Materials. VII. Studies on the Simultaneous Spectrochemical Analysis of Inorganic Constituents with Step Sector Disc.

Studies on the Inorganic Constituents in Biological Materials. VII. Studies on the Simultaneous Spectrochemical Analysis of Inorganic Constituents with Step Sector Disc.

Studies on the Inorganic Constituents n Biological Materials III

The inorganic ccnstituents in biological materials are so small in content and their relative contents differ so much that although their (simultaneous) determination had been desired such was found difficult by the ordinary spectralanalysis. The writers attempted a spectrochemical analysis using a logarithmic sector disc and examined analytical conditions for the determination of Na, K, Mg, Ca, Sr, Ba, Zn, B, Al, and Mn. The spectrograph used was the Zeiss Q. U. 24. The sample was reduced to ash with fuming nitric acid and 30% hydrogen peroxide, derived to a chloride, and placed on an auxiliary electrode of copper. This was excited by continuous arc of 4A, 150V, D, C, for one minute, the paralleled light entering the slit was shielded by a logarithmic sector disc, and record the spectra on the Fuji Al dry plate. The plate was developed by D76 developer and the length of the spectral line was measured under a projector. Nickel was preliminarily added to the sample to be measured as an internal standard. A linear quantitative curve was obtained with each pair of lines as to the relationship between the difference of line length and logarithm of concentration, within a specific concentration range. The analyses were carried out with the brain, liver. heart, kidney, muscle, and lung of five cases of normal rabbit and it was found that a (simultan eous) determination of Na, K, Mg, Ca, and Fe was possible.

Utilisation de la lumière modulée dans les analyseurs photoélectriques pour le dosage de gaz dans le controle industriel

An apparatus is described for following in the factory the progress of a vapour-phase reaction by absorptiometric measurements. The apparatus determines the instantaneous value of the component in a pipe, operates alarm relays if it departs from preselected values, and may control valves. The types of apparatus described are accurate, simple and robust, with electronic amplifiers of rugged type. The detectors used are photo-multiplier cells with chopped beams and electronic a.c. amplifiers; the chopping may be by a sector disc but we have preferred a mercury vapour source modulated at mains frequency. Compensating beam layout of the apparatus is used, and the amplifier has sufficient feedback to secure stability while having enough stages to secure high gain. Standardisation of the amplifier is by two built-in filters giving selected output values. As examples of the application of the apparatus are the estimation of chlorine from 10 −5 to 10 −1, of NO 2 of sulphuric anhydride, of humidity in the range 10–250 mg m 3 .

An Intensity-Compensating System for Infrared Spectrophotometry

A novel compensating device for use in infrared spectrophotometry has been designed, constructed, and its properties investigated. The device consists of two sector disks rotated synchronously, with phase control on one disk permitting an absolute variation of the transmission factor of the compensator. No operational tests on an actual spectrophotometer have been made.

The effect of centring errors on the transmission of a sector disk

Formulae are given for the transmission of rotating sector disks for which the edges of the sectors are not radial with respect to the centre of rotation of the disk. The cases considered include single-aperture disks for beams of various cross-sectional forms and multi-aperture disks for which the edges of the sectors are centred on the same and different points. The formulae indicate how errors due to lack of correct centring can be minimized by suitable construction of the disk.

Testing visual fields by flicker fusion.

THE CRITICAL rate at which a flickering light of decreasing frequency is first perceived to flicker is the one test of visual function in which the light-adapted eye is more sensitive at the periphery of the retina than at its center. Previous investigators have agreed that flicker fusion fields are sensitive and typical in neurological lesions. Phillips 1 (1933) reported two cases of pituitary tumor in which flicker fusion fields proved superior to standard fields. He used a mechanical sector disk method, testing flicker fusion frequency in 17 areas of each field. Riddell 2 (1936) using a similar device and procedure, reported one case in which standard fields showed only a small temporal slant, while flicker fusion fields showed complete hemianopsia. Werner 3 (1942) found pronounced lowering of flicker fusion frequency in 41 patients with various disorders of the central nervous system. Hylkema 4 (1942) found that flicker fusion frequency

Spectrographic Determination of Trace Elements in 70/30 Brass and Admiralty Brass Part I*

A spectrographic procedure for the simultaneous determination of Pb, Fe, Ni, Sn, Bi, and Sb in 70/30 brass and admiralty brass is described in detail. The source is a 14-ampere low voltage d.c. arc of conventional type. A 50-mg pellet sample is arced to extinction in a cupped graphite electrode of specified dimensions. The “intermediate mode” of illumination obtained by focusing the source on the collimator lens is used. A radial sector disk placed at the slit is used to regulate the effective exposure at the plate. The step sector method of plate calibration is used. The source for the calibration is a 4-ampere d.c. arc on 316″ diameter copper electrodes. The calibration curve on the copper line 2882.934A is used for a wave-length region 2590A–3100A. The copper reference line of 2858.734A is chosen for comparison with the respective impurity lines. Working curves are given for the determination of Pb, Fe, Ni, Sn, and Sb in the range of 0.01–0.10 percent and Bi in the range of 0.0004–0.010 percent.

Slotted Cylindrical Rotors for Photometric Calibration

Hollow cylindrical rotors with slotted walls can be used as substitutes for sector disks for some photometric applications. Designs are given of rotors which can replace a logarithmic sector, fixed sector disk, step sector, and variable sector disk. Some of these rotors may be used with non-parallel light. A rotor corresponding to a variable sector disk has been built with a variable slot which can be adjusted to several different openings while inside a vacuum system.

A Speed Control for Sector Disks or Similar Equipment

An apparatus is described by means of which the speed of a sector disk or other reasonably light equipment of similar nature may be accurately controlled and the speed read directly from a set of dials.

Optic Nerve Response to Retinal Stimulation in the Rabbit.

With changes in intensity and duration of light, the retinal potential undergoes slight changes in form, while the nerve discharges show transformations corresponding to the form of the stimulus.The fore part of the rabbit's brain was removed under ether, exposing the optic nerves. Records were taken from one nerve and from across the corresponding retina. Light intensities used were high but within the physiological range, as indicated by reduction of response with reduction of intensity. Experiments were conducted in a dark room, flashes being delivered at about 1 per second from a 2-mm slit in the lamp housing, in front of which a sector disk was rotated. A lens projected an image of the slit on the rabbit's cornea, the eye thus focused an image of the lens on the retina. This image stimulus was compared with one from a diffusing screen close to the cornea illuminated with a 1 ¼-inch spot of light.With flashes as short as 5 ms the retinal potential shows the usual a wave, a diphasic b wave, and no c. T...

Improved arrangement for integrating photometer

The paper gives details of a new simplified type of photometer head incorporating Lummer Brodhun contrast prisms and a sector disc. The use of this head with an integrating photometer is described. When so used, a small portion of the internal surface of the integrator forms one half of the field of view and a comparison disc having an identical surface forms the other half, both surfaces being viewed at the same angle. The advantages of the arrangement are stated.

An equipment for visual spectrophotometry

The paper describes the equipment for visual spectrophotometry designed by the author and installed in the Optics Department of the National Physical Laboratory. The chief features of the equipment are as follows: High light efficiency is obtained by omitting all unnecessary optical parts from the test beam and having independent slit width adjustment for the comparison beam to compensate for the necessary minimum absorption of the measuring apparatus. The basis of measurement is Talbot's law as applied to rotating sectors. A method of employing a series of sectors is described which enables the whole range of effective transmission from 100 to ·01 per cent. to be covered by a series of fixed points, each of which corresponds to a transmission about 90 per cent. of the next higher, with only a few sectors none of which is below 1 per cent. in its effective transmission. A convenient method of calibrating the small-angle sectors is also described. The gaps between the fixed points obtainable by the use of the sector equipment are covered by photometric wedges which are calibrated in terms of the sector disks. The field of the instrument is of the Lummer-Brodhun contrast pattern, which possesses important advantages for spectrophotometry. Adjustments are incorporated which eliminate errors due to lack of accurate parallelism in the specimens tested.

The Use of a Sector Disk in X-Ray Measurements

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text J. A. Becker and Fred W. Warburton, "The Use of a Sector Disk in X-Ray Measurements," J. Opt. Soc. Am. 7, 127-141 (1923) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The Selectiveness of the Eye's Response to Wave-Length and its Change with Change of Intensity.

The present study was undertaken in the attempt to deal quantitatively with the selectiveness of the eye's response. More particularly it sought to determine the chromatic RL at seven points on the spectrum and the number of j. n. d. between the lower and upper chromatic thresholds of the four primary colors. The apparatus was designed to present to O two colored stimuli in a visual field subtending an angle of 1° 55.8' with the surrounding field either dark or equated to the brightness of the stimuli. The variations in energy of physical light required for determinations of chromatic j. n. d. from zero to maximum were effected by means of neutral grey gelatine filters and sector disks devised especially for liminal work. The method of limits was the procedure employed for arriving at the j. n. d. With the dark surrounding field it was found that liminal chromatic sensitivity increased in the following order: O, R, Y, BG, B, YG, and G. With the light surrounding field the order was: O, Y, R, YG, B, G, and BG. At the upper threshold, with the dark field, decreasing sensitivity followed the order of YG, G, O, B, BG, R, and Y; with the light field, YG, G, O, BG, B, R, and Y. In the work on chromatic discrimination with the four primary colors it was found that with the dark field Y, G, R, and B reached their maximum points of saturation at the 20th, 32nd, 40th, and 55th j. n. d. respectively; with the light field Y, G, B, and R reached their maxima at the 46th, 70th, 72nd, and 81st j. n. d. From Psych Bulletin 20:05:00336. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

Note on Mr. Mallock's observations on intermittent vision

In the paper communicated by Mr. Mallock on December 11, 1913, in order to account for the intermittences seen when watching a resolving disc or black and white sectors, at the moment when a slight mechanical shock is given to the head or body, he advances the hypothesis that a slight mechanical shock of any kind produces a periodic but rapidly extinguished paralysis of the perception of light, and that the nerves on which seeing depends cannot bear more than a certain amount of mechanical acceleration without loss of sensibility. This hypothesis of a momentary paralysis of the sense of vision seems unnecessary. The sector disc revolving at from two to six revolutions per second presents a uniform grey tint. At the moment when the intermittence occurs, by stamping the foot or tapping the head, the most prominent effect observed by the writer was not the momentary appearance of stationary grey or block sectors, but the enhanced brightness of stationary white sectors. A momentary paralysis, if it occurred, should produce momentary blackness of the entire disc, which is not what happens.