1、BRITISH STANDARD BS ISO 9358:1994 Implementation of ISO 9358:1994 Optics and optical instruments Veilingglare of image-forming systems Definitionsand methods of measurementBSISO9358:1994 This British Standard, having been prepared under the directionof the Consumer Products and Services Sector Board
2、 (W/-), was published underthe authority of the Standards Board and comesintoeffect on 15 February 1995 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference CPM/17 Draft for comment 91/45537 DC ISBN 0 580 23841 5 Committees responsible for this BritishSta
3、ndard The preparation of this British Standard was entrusted to Technical Committee CPM/17, Fundamental Aspects of Optical Standards, upon which the following bodies were represented: Department of Trade and Industry (National Physical Laboratory) Engineering Equipment and Materials Users Associatio
4、n Flat Glass Manufacturers Association Ministry of Defence Sira Limited Society of British Aerospace Companies Limited United Kingdom Laser and Electro-optic Association Amendments issued since publication Amd. No. Date CommentsBSISO9358:1994 BSI 01-2000 i Contents Page Committees responsible Inside
5、 front cover National foreword ii Foreword iii Text of ISO 9358 1BSISO9358:1994 ii BSI 01-2000 National foreword This British Standard reproduces verbatim ISO 9358:1994 and implements it as the UK national standard. This British Standard is published under the direction of the Consumer Products and
6、Services Sector Board whose Technical Committee CPM/17 has the responsibility to: aid enquirers to understand the text; present to the responsible international committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; monitor related international and Europ
7、ean developments and promulgate them in the UK. NOTEInternational and European Standards, as well as overseas standards, are available from Customer Services, BSI, 389 Chiswick High Road, London W4 4AL. A British Standard does not purport to include all the necessary provisions of a contract. Users
8、of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theISO title page, pages ii to iv, pages 1
9、to 19 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.ISO9358:1994(E) ii BSI 01-2000 Contents Page Foreword iii Introduction 1 1 Scope 2 2 Definitions 2 3 Classific
10、ation of test specimen 3 4 Measurement methods 3 5 Test conditions 14 6 Specification of measurement conditions 17 7 Points requiring special attention during veiling glare measurements 17 8 Presentation of results 18 Figure 1 Veiling glare measurement in the case of an unlimited object field 5 Figu
11、re 2 Veiling glare measurement with unlimited object field and infinite object distance 6 Figure 3 Veiling glare measurement with unlimited object field using an auxiliary lens 6 Figure 4 Schematic diagram of square box type radiation source 7 Figure 5 Equipment for measurement of veiling glare at f
12、inite object distance 8 Figure 6 Equipment for measuring glare spread function 9 Figure 7 GSF plot and method of normalisation 10 Figure 8 GSFR plot and method of normalisation 11 Figure 9 Source systems 12 Figure 10 Equipment for measurement of GSF or GSFR of a lens with finite object distance 12 F
13、igure 11 Equipment for measuring GSF of an image intensifier tube 13 Table 1 3 Table 2 4ISO9358:1994(E) BSI 01-2000 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International St
14、andards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also
15、 take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an Internatio
16、nal Standard requires approval by at least 75% of the member bodies casting a vote. International Standard ISO9358 was prepared by Technical Committee ISO/TC 172, Optics and optical instruments, Subcommittee SC 1, Fundamental standards.iv blankISO9358:1994(E) BSI 01-2000 1 Introduction The image pla
17、ne of an optical or electrooptical imaging system normally receives not only the image forming radiation, but also stray (unwanted) radiation which can reduce image contrast. This unwanted radiation is referred to as “veiling glare”. In lens systems it usually arises from one or more of the followin
18、g causes: a) internal multiple reflections between the lens surfaces; b) scatter from the surfaces of the lens elements due to scratches and other imperfections in the polish, dirt and dust, fingerprints, grease, poor antireflection coatings and faulty reflective coatings on mirrors; c) bulk scatter
19、 from the interior of the glass and from bubbles and striae; d) scatter from optical cements; e) scatter and reflections from ground edges of the lens elements, from internal lens mounts and from the internal surfaces of the lens barrel; f) reflections from the surfaces of diaphragms and shutter bla
20、des; g) fluorescence of the glass optical cements. The veiling glare of lens on its own can be considerably different from the veiling glare of a lens system and camera body combination. In the latter case, reflection of part of the image-forming radiation from the photosensitive material in combina
21、tion with further reflections and scatter from the lens system and camera body contribute significantly to the veiling glare. In electrooptical devices, veiling glare arises from similar causes. For instance, in an image intensifier tube glare can arise from: a) radiation transmitted through the pho
22、tocathode being scattered and reflected by internal structures back onto the photocathode; b) radiation emitted from the phosphor going back to the photocathode; c) in tubes with microchannel plates some electrons incident on the input face can be back-scattered from this face before returning to it
23、 with the primary electrons. For the purposes of this International Standard, it is important to differentiate between veiling glare which originates from radiation incident on the entrance pupil or input face of an optical or electrooptical system and other factors which may cause a reduction in co
24、ntrast and which may therefore influence a measurement of veiling glare. Examples of these are: a) radiation entering a system through leaks in the casing or body of the system; b) radiation from internal sources in a system such as LEDs; c) reflection of ambient radiation from projection screens or
25、 CRT displays; d) dark current in electrooptical devices; e) fog in photographic emulsions. There are two principle methods of measuring veiling glare, namely the integral (or black patch) and the analytical (or glare spread function). In the integral method, the target object is a small black area
26、surrounded by an extended uniform source. The veiling glare index (VGI) is specified as the ratio of the irradiance in the image of the black area to the irradiance in the image of the extended source. For definitions of this and other radiometric and photometric terms, see ISO 31-6. In the analytic
27、al method, the object is a small source with a dark surround. The distribution of irradiance in the image plane normalised in a particular way, is defined as the glare spread function (GSF). Each of these two methods of measuring veiling glare has its own particular areas of usefulness. In general,
28、the integral method is applicable to systems where the scene will normally be of roughly uniform radiance (e.g. a landscape photographed in overcast conditions or with the sun behind the camera) whilst the analytical method is relevant to applications where intense isolated sources may be present in
29、 the scene (e.g. a star sensor system on a space vehicle, designed to operate with the sun just outside its field of view). The analytical method has the further advantage that in principle it can be used to calculate glare levels in a specified real situation and in fact the VGI can be predicted fr
30、om the GSF (e.g. by convolution and integration of the GSF with the radiance distribution in the scene) whilst the reverse is not possible.ISO9358:1994(E) 2 BSI 01-2000 1 Scope This International Standard adopts both the veiling glare index (VGI) and the glare spread function (GSF) as measures of th
31、e veiling glare characteristics of optical and electrooptical imaging systems. Laboratory measurement techniques are described in general terms and recommendations are made regarding the performance of the main subunits of the equipment. The measurement techniques described in this International Sta
32、ndard are chiefly valid for the visual spectral range. For adjacent spectral ranges, modifications of these techniques will possibly be necessary. Standard methods of specifying conditions of test and of expressing the results are given, while to assist in the intercomparison of VGI figures, standar
33、d test conditions are specified. This International Standard also gives guidelines for the operation of measuring equipment such that accurate results can be achieved. Results of veiling glare index measurements made using equipment which does not conform in detail to the configurations described in
34、 this International Standard are accepted as valid, provided the method of measurement is substantially similar (i.e. measures the ratio of the radiance in the image of the black area to the radiance in a surrounding bright field) and provided the test results can be correlated to the required accur
35、acy with results obtained on equipment which conforms strictly to this International Standard. 2 Definitions For the purposes of this International Standard, the following definitions apply. 2.1 veiling glare unwanted irradiation in the image plane of an optical or electrooptical system, caused by a
36、 proportion of the radiation which enters the system through its normal entrance aperture. The radiation may be from inside or outside the field of view of the system 2.2 veiling glare index (VGI) ratio of the irradiance at the centre of the image of a small, circular, perfectly black area superimpo
37、sed on an extended field of uniform radiance, to the irradiance at the same point of the image plane when the black area is removed. VGI is expressed as a percentage unless otherwise specified NOTE 1The size of the black area and of the surrounding field, as well as the proportion of the black area
38、used for measurement, shall be specified. 2.3 veiling glare index band target (VGIB) ratio of the irradiance at a specified position along the centreline of the image of a narrow, perfectly black band superimposed on an extended field of uniform radiance, to the irradiance at the same point of the i
39、mage plane when the black band is removed. VGIB is expressed as a percentage unless otherwise specified NOTE 2The black band, or strip, shall extend across a diagonal of the image format. Its width and length, as well as the size of the surrounding field and the proportion of the black area used for
40、 measurement shall be specified. 2.4 glare spread function (GSF) irradiance distribution in the image plane, produced by a small source object, normalised to unit total flux in the on-axis image of the small source GSF is expressed in units of reciprocal square metres (m 2 ) the GSF only has meaning
41、 outside the primary image of the source i.e. GSF irradiance due to veiling glare total flux in image of source - =ISO9358:1994(E) BSI 01-2000 3 2.5 glare spread function radiant intensity (GSFR) radiant intensity in image space of an equivalent veiling glare source at the exit pupil of the test sys
42、tem which gives rise to the measured veiling glare irradiance in the image plane. This intensity is normalised to unit total flux in the on-axis image of the actual illuminating source GSFR is expressed in units of reciprocal steradians (sr 1 ) GSFR is normally used in preference to GSF when dealing
43、 with afocal systems. GSFR only has meaning outside the primary image of the source 3 Classification of test specimen The arrangement of test equipment used in measuring veiling glare will depend on the test specimen and shall be representative of the conditions under which it will normally be used.
44、 Table 1 illustrates how these conditions are classified for the purpose of this International Standard and gives examples of classifications for typical specimens. The classification given in Table 1 is based on object distance and area and image distance and as shown in Table 2. 4 Measurement meth
45、ods 4.1 Veiling glare index 4.1.1 General technique A typical arrangement for measuring the VGI of a lens is illustrated diagrammatically in Figure 1. The extended bright field (subtending 2; sr in this case) is produced by illuminating an integrating sphere with several lamps through suitable porth
46、oles. The “black area” is an absorbing cavity in the wall of the integrating sphere which can be interchanged with a section having the same reflecting characteristics as the remainder of the internal surface of the integrating sphere. The lens under test is placed with its front end protruding into
47、 an exit port which is diametrically opposite the “black area” in the integrating sphere. The front of the lens should protrude into the sphere at least as far as the line of the integrating surface. The irradiance in the image of the black area is measured with a suitable photoelectric detector in
48、front of which is a small aperture (with, if necessary a small integrating sphere, or condenser lens system, and/or diffuser between the two). Table 1 Object distance Image distance Infinity or greater than10 focallength Finite Finitebutinaccessible A Object at infinity or greater than 10 focal leng
49、th (unlimited object area) Telescopes, also image intensifier telescopes Photographic lenses TV systems, cameras, cine cameras B Finite (limited object area) Projection lenses, magnifiers, microscopes Enlarging lenses, process lenses, photographic lenses, image converter tubes with fibre plates TV microscopes C Finite but not directly accessible/(limited object area) (Microscopes) Image converter tubes with glass discs (TVmicroscopes) i.e. GSFR radiant i
