Study of the photosensitivity of new photothermoplastic materials under conditions that most closely approximate the taking of pictures of earth from space

  • Published on
    08-Oct-2016

  • View
    212

  • Download
    0

Embed Size (px)

Transcript

  • ep

    V.

    ps,etrthers

    quencies, contrasts, and luminances ~in all, 216 versions ofone image!. With the appropriate reduction, this test objectmakes it possible to form on PTPMs an optical image withgiven parameters. The goal of this paper is to use this testobject to develop a sensitometric apparatus for testing aero-space photographic materials under conditions that approachas closely as possible the conditions for taking pictures of theearth from space, and to determine the sensitometric photo-sensitivity and exposure indices of the new high-resolutionPTPMs with a compact structure on a rigid substrate.3,4

    SENSITOMETRIC APPARATUS

    The apparatus for studying photosensitivity under condi-tions that approach as closely as possible the conditions un-der which pictures of the earth are taken from space ~Fig. 1!includes the following: test object2 1; the radiation source,

    of the PTPM is made in the form of a GOI FP-90M dark-field schlieren system,1 which works in transmitted light, anda dark-field schlieren system based on an MBS-10 opticalmicroscope operating in transmitted and reflected light.

    The test object ~Fig. 2! is based on a periodic latticeconsisting of alternating light and dark lines extending in thehorizontal direction. Each line is 5 mm long. The width ofthe lines discretely increases in the vertical direction. Thereare six lines of identical width: three light and three dark~three periods!. These six lines form a frequency field corre-sponding to one spatial frequency. The first version of thetest object contains thirty-eight fields with frequencies from4.0 to 0.29 mm21, the second contains twenty-nine with fre-quencies of 8.0 0.16 mm21, and the third contains forty-twowith frequencies of 2.0 0.47 mm21. Three versions of thetest object were required for the following reason. On onehand, the test object must contain a large range of spatialStudy of the photosensitivity of new photoththat most closely approximate the taking of

    Yu. A. Cherkasov,* E. L. Aleksandrova, and M.

    S. I. Vavilov State Optical Institute, St. Petersburg, Russia~Submitted June 4, 1998!Opticheski Zhurnal 66, 6165 ~July 1999!An apparatus has been developed for determining thefrom an optical test image with contrasts, frequenciepictures of earth are made from space. The sensitomhave been determined for new high-resolution photocompact structure on a rigid substrate. For various vequal 12.550 and 10 40 lux21 sec21, respectively.@S1070-9762~99!00707-1#

    The main requirement of sensitometry is to bring theexperimental conditions as close as possible to the practicalconditions of picture taking ~so as to provide the most ad-equate reproduction!, and this is satisfied fairly well in thesensitometry of silver halide photographic materials. How-ever, it is not always possible to satisfy this requirement fornew types of photographic materials, including photothermo-plastic materials ~PTPMs!, for which there are no standardtest methods.1 It is fairly easy to choose a picture-takingregime for the high-quality recording of simple objects onPTPMs, for example a spatial lattice of one definite fre-quency, with contrast and brightness that are identical overthe entire frame. However, a substantially more complex pat-tern of brightness distribution is observed in taking picturesof the earth from space, while the shape and size of objectsand their contrast is extremely varied. This has the effect thatthe sensitometric photosensitivity determined in terms of thestandard density for large fields can strongly differ from thepractical photosensitivity determined by the so-called expo-sure index from an optimum image containing various spa-tial frequencies with a wide range of contrasts and lumi-nances corresponding to what is observed in taking picturesof earth from space. Therefore, Ref. 2 developed and studieda special test object that contained, along with a sensitomet-ric wedge, a set of three-bar targets of various spatial fre-628 J. Opt. Technol. 66 (7), July 1999 1070-9762/99/07062rmoplastic materials under conditionsictures of earth from spaceSmirnov

    hotosensitivity of photographic materialsand radiances that occur whenic photosensitivity and exposure indexermoplastic materials with aions of the materials, these quantities

    1999 The Optical Society of America.

    including illuminator 2, scatterer 3, and conversion light fil-ter 4; projection objective 5; shutter 6; photothermoplasticcamera 7, with PTPM 8 and control unit 9; test system 10;and visualization system 11, with measurement of the opticaldensities in transmitted and reflected light.1 The test objectmakes it possible to use the objective to form an opticalimage on the layer with frequencies 2 200 mm21, contrast0.0150.65, and luminances of the lines on the test objectvarying within 1.5 orders of magnitude. The illuminatorsconsist of two 1-kW halogen incandescent lamps whosecolor temperature ~3200 K! is reduced by filter 4 to that ofthe sun ~5500 K!. Moreover, illuminators were used in theform of flashlamps with Tcol55600 K and drive number 24~the flash time is 1024 sec) ~not shown in Fig. 1!. The illu-minance in the plane of an image of the fields of the wedgeis determined by means of a secondary detector with an errorof 65%. The luminance of the source is calibrated by pho-tographic photometry from the luminance of a photometricsphere. The illuminance in the plane where the PTPM ismounted is measured with a Yu-16 luxmeter. The E ra-27objective has a modulation transfer function close to that forthe actual Apo-Mars aerospace objective with which sensi-tometric tests of the PTPM were carried out earlier.7 Theshutter provides delays of from 1 to 0.001 sec. The systemfor visualizing the relief-phase image formed on the surface6288-04$15.00 1999 The Optical Society of America

  • frequencies in order to determine high resolving power athigh contrast and optimal exposure and low resolving powerat low contrast and nonoptimal exposures on one frame. Onthe other hand, the discretization step of the spatial frequen-cies must be small. It follows from these two requirementsthere must be a large number of frequency fractions. Themaximization of the range of spatial frequencies and theminimization of the discretization step of these frequenciesare mutually contradictory requirements. Therefore, the firstversion of the test object is a certain compromise betweenthem. In the second version, the frequency range is increasedto cover a factor of 51.2, and, in the third, conversely, byreducing the frequency range to cover a factor of 4.2, thefrequency discretization step is reduced to 2.55%. In eachversion of the test object, each frequency field is repeatedthirty-six times. In this case, the contrast between the lightand dark lines and their mean optical density change. Themean optical density has six values. They correspond to sixwide vertical columns into which the frequency part of thetest object is divided. Each of the indicated wide columnscontains frequency fields of six different contrasts. The upperand lower parts of the test object include sensitometricwedges from eight fields with dimensions of 30320 mmeach.

    FIG. 1. Layout of apparatus for studying the photosensitivity of PTPMs ~seetext for explanation!.

    FIG. 2. Test object for studying the photosensitivity of PTPMs.629 J. Opt. Technol. 66 (7), July 1999Studies were carried out for PTPMs with compactstructure.3,4 The PTPM is made on a rigid glass substrate, onwhich a raster, a thermal-developing conductive electrode,contacts to it, a protective layer, a CdSe injection layer 0.10.4 mm thick, and a thermoplastic layer 3 mm thick are suc-cessively deposited. Recording was done on the PTPM fromthe side of the glass substrate through the raster.

    The photothermoplastic cell is made in a dust-and-moisture-proof version and has separate optical input andoptical output. Besides the PTPM, the cell contains acorotron for electrostatically sensitizing the PTPM. It ismade in the form of a multifilament system with an equaliz-ing grid and counterelectrode. All the detachable parts of thesystem are sealed. The moisture is minimized by a desiccantplaced in special recesses of the system. Plug-and-socketunits for supplying high voltage, for developing and erasingcurrent pulses, and for the thermostatic control system arelocated on the housing of the cell. The photothermoplastic-recording process-control unit optimizes the sensitization,exposure, thermal development, and thermal erasure re-gimes, as well as keeping the temperature in the cell constantat 4061 C. A sequential photothermoplastic recording pro-cess is used, including sensitization of the PTPM by depos-iting a surface electrostatic charge, exposing it, and ther-mally developing it by Joule heating evolved in theconductive layer when current passes through it. The record-ing regimes are specified by the control unit.

    RESULTS OF THE STUDY

    A characteristic curve for a PTPM with a CdSe layer 0.1mm thick, constructed from the results of a measurement ofthe optical density of the fields of the photothermoplasticimage in a thermal-field schlieren system, is shown in Fig. 3.The same figure shows resolvometric curves for various con-trasts of the optical image. In constructing the resolvometriccurves, thirty-six values were obtained for the resolvingpower of the PTPMs as a function of contrast for six zones offrequency fields with different optical densities. The contrastof the optical image is defined as the product of the contrastof the frequency field of the test object and the correspond-ing value of the frequency-contrast characteristic of the ob-

    FIG. 3. Characteristic curve ~I! and the corresponding resolvometric curves~II! for PTPMs on a CdSe base: ~a! perpendicular and ~b! parallel orientationof the PTPM raster relative to the lines of the test object. The contrast of theoptical image is indicated near the curves.629Cherkasov et al.

  • ve

    TABLE II. General sensitometric of PTPMs with a CdSe layer 0.1 mmthick.

    Characteristic

    Photosensitivity numbwith D5Dmax20.8

    Exposure index, lux2Photographic latitudeMaximum contrast coMaximum optical denMinimum optical denMean gradient g

    se ~1!, type 58 aerialfilm for professional

    630 J. Opt. TeValue

    er, lux21 sec215

    12.5

    1 sec21 10L 1.3efficient gmax 1.4sity Dmax 2.3sity Dmin 0.3

    0.9FIG. 4. Characteristic curves of PTPMs on a CdSe baphotographic film ~2!, and KN-2 negative photographicmotion-picture photography ~3!.jective being used. The data of Fig. 3a refer to a perpendicu-lar orientation of the raster relative to the lines of the testobject, and the data of Fig. 3b refer to a parallel orientation,for which the maximum resolvable frequency is limited bythe Nyquist frequency, equal to twice the lattice period. Us-ing the characteristic curve for the standard density of 0.85above the fogging density D0 , taken for aerial photographicplates ~for the direct positive photothermoplastic process, D5Dmax20.85), the photosensitivity numbers are defined asS0.85510/H ~in lux21 sec21), where H is the exposure thatcreates the standard density.5,6 It is used to determine theexposure H0 corresponding to the maximum resolving powerfor various contrasts of the optical image. By comparing H0with the exposure H that creates the standard density and byusing the photosensitivity number S0.85 , the exposure indexEI5S0.85H/H0 is determined. The S and EI values obtainedfor five versions of the PTPMs are shown in Table I. As canbe seen from this table, the photosensitivity increases from12.5 to 50 lux21 sec21 and EI increases from 10 to40 lux21 sec21 as the CdSe layer thickness goes from 0.1 to0.4 mm. In this case, the maximum resolving power for acontrast of 0.2 decreases from 240 to 90 mm21, while thespatial frequency corresponding to a modulation-transfer co-efficient ~MTC! of TN50.5 decreases from 130 to 25 mm21.The other general sensitometric characteristics of the PTPMsare determined from the characteristic curves: the photo-graphic latitude L , the contrast coefficient g, the mean gra-dient g , the maximum density Dmax , and the minimum den-sity Dmin . The general sensitometric properties of a PTPMwith a CdSe layer 0.1 mm thick are given in Table II. As canbe seen from Tables I and II, the resulting photosensitivityvalues meet the requirements of aerospace photography ~noless than 10 lux21 sec21, Ref. 2!.

    An additional verification of the value obtained for thephotosensitivity is obtained by combined testing of PTPMs

    TABLE I. Photosensitivity and exposure index of fivelayer.

    dCdSe ,mm

    Slux21 sec21

    EIlux21 sec21

    0.10 12.5 100.15 18 150.20 25 200.30 37.5 300.40 50 40chnol. 66 (7), July 1999and silver halide photographic plates. Two types of films arechosen for comparison:8 film for professional cinematogra-phy ~KN-2 negative! and aerial-photography film ~type 58isopanchromatic!. The spectral sensitivity regions of thesefilms are close to that of the PTPM. This makes it possible tocompare the sensitivities of the materials using light sourceswith different color temperatures, including standard sources~3200 and 5500 K!. The general sensitometric characteristicsof the films were first determined by the standard technique,using standard devices. The photosensitivity number S0.150.8/H of KN-2 film was 50 lux21 sec21, and S0.85510/Hof type 58 isopanchromatic film was 40 lux21 sec21. Afterthis, the photographic film and the PTPM were exposed onthe new apparatus. The characteristic curves constructedfrom the results of the exposure are shown in Fig. 4, and theresulting photosensitivity numbers are given in Table III. Ascan be seen from Table III, the photosensitivity numbers ofthe photographic materials coincide with those determinedabove, which further confirms the correctness of the photo-sensitivity measurements of the PTPMs.

    The photosensitivity spectrum in the near IR and UVregions is given in Fig. 5 ~curve 1! for the PTPM studiedhere, with a thickness of the CdSe injection layer of dCdSe50.4 mm. It also shows the photosensitivity spectra ofPTPMs with different dCdSe values. A PTPM with no injec-tion layer is sensitive in the UV region ~curve 2!, and PTPMswith thicker CdSe layers are sensitive in the x-ray and granges ~curves 35!.

    rsions of PTPMs differing in the thickness of the CdSe

    Rmaxwith k50.2, mm21

    Nwith MTC50.5, mm21

    240 130180 100120 60100 3090 25630Cherkasov et al.

  • REPRODUCIBILITY

    The reproducibility of the photosensitivity of the mate-rial is most important for ensuring the reproducibility of itsresolving power, which depends on the position of the reso-lution curve relative to the characteristic curve.9 The repro-ducibility of the photosensitivity was determined from thereproducibility of the resolvometric curves. The results ap-pear in Fig. 4, on which the vertical lines show the scatter ofthe results in a series of seven measurements made on seven

    The authors are grateful to A. L. Kuznetsova and Yu. M.Chesnokov for discussing the results. The work was per-formed under grant INTAS-93-6...

Recommended

View more >