1、October 2010 Translation by DIN-Sprachendienst.English price group 16No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).IC
2、S 37.020!$kTu“1724982www.din.deDDIN ISO 11421Optics and optical instruments Accuracy of optical transfer function (OTF) measurement(ISO 11421:1997)English translation of DIN ISO 11421:2010-10Optik und optische Instrumente Genauigkeit von Messungen der optischen bertragungsfunktion (ISO 11421:1997)En
3、glische bersetzung von DIN ISO 11421:2010-10Optique et instruments doptique Exactitude du mesurage de la fonction de transfert optique (OTF) (ISO 11421:1997)Traduction anglaise de DIN ISO 11421:2010-10SupersedesDIN ISO 11421:2005-09www.beuth.deIn case of doubt, the German-language original shall be
4、considered authoritative.Document comprises 34 pages10.10 DIN ISO 11421:2010-10 2 A comma is used as the decimal marker. Contents Page National foreword 3 National Annex NA (informative) Bibliography 3 Introduction.4 1 Scope .5 2 Normative reference .5 3 Definitions and symbols 5 4 Sources of inaccu
5、racy in measuring equipment .7 5 Methods of assessing levels of accuracy . 14 6 Calculation of overall accuracy of a measurement . 22 7 Specifying a general equipment accuracy 23 8 Routine performance evaluation 26 Annex A (normative) Accuracy of PTF measurement 28 Annex B (informative) Determinatio
6、n of rate of change of MTF various parameters 29 Annex C (informative) Example calculation of NAV 31 Annex D (informative) Bibliography 34 DIN ISO 11421:2010-10 3 National foreword This standard has been prepared by Technical Committee ISO/TC 172 “Optics and photonics”, Subcommittee SC 1 “Fundamenta
7、l standards”. The responsible German body involved in its preparation was the Normenausschuss Feinmechanik und Optik (Optics and Precision Mechanics Standards Committee). The DIN Standard corresponding to the International Standard referred to in this document is as follows: ISO 9334 DIN ISO 9334 Am
8、endments This standard differs from DIN ISO 11421:2005-09 as follows: a) wrong equations have been corrected; b) Figure B.1.b) has been corrected. Previous editions DIN ISO 11421: 2005-09 National Annex NA (informative) Bibliography DIN ISO 9334, Optics and photonics Optical transfer function Defini
9、tions and mathematical relationships DIN ISO 9335, Optics and photonics Optical transfer function Principles and procedures of measurement DIN ISO 9336-3, Optics and optical instruments Optical transfer function; Application Part 3: Telescopes Introduction The optical transfer function (OTF) is one
10、of the main criteria used for objectively evaluating the image-forming capability of optical, electro- optical and photographic systems. The terms used in the measurement of OTF are defined in IS0 9334, whilst IS0 9335 covers the actual principles and procedures of measurement. A further Internation
11、al Standard, IS0 9336, deals with specific applications in various optical and electro-optical fields and is in several parts, each dealing with a particular application. Although IS0 9335 lists the main factors which influence the accuracy of OTF measurement and describes procedures which are aimed
12、 at achieving accurate and repeatable results, it does not cover in detail the techniques and procedures for evaluating the accuracy of OTF measuring equipment and for estimating the uncertainty in measurements made on specific imaging systems. The present International Standard lists the main sourc
13、es of inaccuracy in OTF measuring equipment and provides guidance on how these can be assessed and how the results of these assessments can be used in estimating the error band in any measurement of OTF. One of the aims in preparing this International Standard is to encourage the setting of more rea
14、listic uncertainty levels for the results of OTF measurements. Another is to encourage the use of methods of expressing the accuracy of OTF test equipment which recognize the fact that the accuracy of a particular measurement is a function of both the equipment and the test piece. 4DIN ISO 11421:201
15、0-10 Optics and optical instruments Accuracy of optical transfer function (OTF) measurement 1 SCOPE This International Standard gives general guidance on evaluating the sources of error in optical transfer function (OTF) equipment and in using this information to estimate errors in a measurement of
16、OTF. It also gives guidance on assessing and specifying a general accuracy value for a specific measuring equipment, as well as recommending methods of routine assessment. The main body of this International Standard deals exclusively with the modulation transfer function (MTF) part of the OTF. The
17、phase transfer function (PTF) is dealt with relatively briefly in annex A. 2 NORMATIVE REFERENCE The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All st
18、andards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0
19、 9334:1995 Optics and optical instruments - Optical transfer function - Definitions and mathematical relatbnships 3.1 DEFMWTiONS For the paarposes of this International Standard, the following definitions apply. 3.M standard lens Single- or multi-element lens which has been constructed with a level
20、of accuracy which is sufficient to ensure that for precisely specified conditions of measurement the MTF will be equal to that predicted from theoretical calculations to an accuracy of better than 0,05 (MTF units). NOTE - In order to achieve this accuracy, standard lenses are usually of simple const
21、ruction and therefore of limited performance. An example of a widely used lens is the 50 mm focal length plano-convex lens described in reference 3. This and several other standard test lenses (including afocal systems and lenses operating in the infrared wavelength bands) are available commercially
22、. 3.1.2 audit lens Single- or multi-element lens of stable construction whose accuracy of construction is not sufficient to enable the MTF to be predicted by calculation from design data (usually as a result of the complexity of the lens), but whose “accepted” values for the MTF under precisely defi
23、ned measuring conditions have been obtained by measurements done by a reputable authority (preferably a national standards laboratory, if such a service is available). 5DIN ISO 11421:2010-10 3.2 SYMBOLS Symbol h h Ah 1 1 Al1 AZ AZ/ Aa Aa AZ ti M r Ar d-h) m(r,h) or m(r,cu) pkh) or p(w) q( rh) 0 AW f
24、 w Aw R g L MTFc r n( r,h) AMTF(r) AMTFJ r) AMTF, Al AMTF(random) AMTF (systematic) AMTF(totaI) AMTF( rand)” AMTF(syst)n object height image height Meaning error in image height object conjugate image conjugate error in image distance departures from straightness of object slide departures from stra
25、ightness of image slide angular departure of object slide from perpendicularity to reference axis angular departure of image slide from perpendicularity to reference axis total departure from ideal object plane total departure from ideal image plane magnification spatial frequency error in spatial f
26、requency rate of change of MTF with object focus (for image intensifier and similar systems) rate of change of MTF with image focus rate of change of MTF with image height rate of change of MTF with image distance field angle error in field angle focal length azimuth angle error in azimuth angle bet
27、ween slits (test lens focal length)/(colIimator focal length) or (decollimator focal length)/(collimator focal length) width of slit referred to image plane length of shorter slit referred to image plane MTF of relay lens spatial frequency for zero field angle rate of change of MTF with spatial freq
28、uency error in MTF MTF error of the relay lens MTF errors resulting from aberrations of relay lens error error in setting collimator focus total error in MTF random sources total error in MTF systematic sources total error in MTF from all sources error in MTF from nth source of random error error in
29、 MTF from rzth source of systematic errors Unit mm, mrad, degree mm, mrad, degree mm, mrad, degree mm mm mm mm mm rad rad mm mm dimensionless mm -I, mrad-I, degree-l mm -I, mrad-I, degree-l mm -1 mm -1 mm -I, mrad-I, degree-l mm -1 mrad, degree mrad, degree mm degree degree dimensionless mm mm dimen
30、sionless mm -I, mrad-I, degree-l mm, mrad, degree dimensionless dimensionless dimensionless mm dimensionless dimensionless dimensionless dimensionless dimensionless NOTE - The notation Id Jz” are object and image heights, iVlumina%e the aperture of a collimator. T GENERATOR (4.10). The requirements
31、are is only required to uniformly 4.12 EQUIWIEMT SdGNAL PROCESSING Err.ors in the MTF measurement can arise from limitations and inaccuracies in the signal processing of the measuring equipment. The magnitude of such errors can be estimated from measurements carried out using standard test lenses or
32、 special artefacts such as accurately measured slits (see 5.6). 4.13 STRAY RADIATION Stray radiation from such sources as room lighting may affect the performance of an equipment. This should be checked by the user and any undesirable sources of radiation eliminated or reduced to a level at which th
33、eir effects are insignificant. 4.14 COHERENT RADIATION The concept of OTF as it is dealt with in this International Standard applies only to objects which are illuminated incoherently. The use of coherently, or partially-coherently, illuminated test objects for the measurement of OTF will give incor
34、rect results. No easy means of assessing the degree of coherence or partial-coherence of a test object exists. The necessary steps to avoid coherent illumination are part of the design of an equipment and are not dealt with in this standard. Apart from avoiding the use of coherent sources such as la
35、sers, a necessary condition of illumination is that the numerical aperture (NA) of the optical system illuminating the test object shall be greater than the object-side NA of the test piece (for collimated radiation the pupil of the collimator shall also be greater than that of the test piece). When
36、 13DIN ISO 11421:2010-10 testing systems with large NAs (such as microscope objectives), care is required to ensure that this condition still holds. No such problem exists with self-luminous test objects. 4.15 BASELINE ERROR If the signal baseline (i.e. zero level) used in a measurement of MTF is in
37、correct, the result can have significant errors. Departures from the correct baseline are typically a result of sensitivity of the equipment to ambient lighting, uncompensated, or incorrectly compensated, detector dark current and signal offsets from misadjustment of the electronic circuits. In many
38、 electro-optical systems the image normally sits on a non-zero background. Baseline errors occur if this background is incorrectly subtracted from the measured signal. The accuracy of the baseline can be checked by comparing the assumed level with that obtained when the object generator source is sw
39、itched off or when the test pattern is replaced by a blank pattern. The two levels should be the same. 5 METHODS OF ASSESSING LEVELS OF ACCURACY In this clause techniques are described for making the quantitative measurements which enable a value to be given to the possible errors arising from some
40、of the sources listed in clause 4. Alternative methods of making these measurements exist in most cases. They may be used provided they have the necessary accuracy. Many of the measurements can be made using well-known techniques and are therefore not described in this International Standard. In mos
41、t instances both systematic and random errors exist, and both should be assessed. 5.1 GEOMETRY OF OPTICAL BENCH SYSTEM 5.1 .I Straightness of slideways This refers principally to the overall flatness or straightness of the line or plane over which the image analyser and/or TTU move and which therefo
42、re defines the image and/or object planes. Departures from the ideal pla the slideway which carries ne are the im usu ally caused by lack of straig we analyser or l-w. htness and/or crosswind (see figure 2) in Various well-established techniques exist for measuring straightness and crosswind. The me
43、thod recommended here is to make a direct measurement of their combined effect using a sensitive linear distance transducer and a reference straightedge or plane. The arrangement is illustrated in figure 3. The transducer is mounted in the position normally occupied by the image analyser or TTU, wit
44、h the measuring probe along what would normally be their optical axes. The reference plane or straightedge is mounted parallel to what should be the image/object plane or measurement diagonal (i.e. perpendicular to the reference axis). The probe is arranged so that it measures directly the variation
45、 in distance between the reference plane or edge and what would be the positions of the image analyser or TTU as they move along the slideway. The reference axis is usually taken as being an axis perpendicular to the surface on which the optical system reference mounting flange (or equivalent) will
46、locate. The straightedge or reference plane is therefore set parallel to this, either using an autocollimator and suitable plane mirror(s), or in fact by mounting them directly on this surface, This measurement technique gives results which include the effect of any overall angular deviation from pe
47、rpendicularity to the reference axis. 14DIN ISO 11421:2010-10 NOTE - for some optical systems the reference mounting surface may be parallel to rather than perpendicular to the reference axis (e.g. a lens with a cylindrical body concentric with its optical axis, may use the cylindrical surface as th
48、e reference mounting surface) and the alignment technique must be adapted accordingly. Cross wind (in p field slide) P R H 0 F M C B (a) (b) (cl Lens under test Lens reference surface (flange) Image plane Field slide Focal slide Image analyser Collimator Axis of rotation Straightness errors Slideway
49、 misalignment Cross wind errors Figure 2 - Mechanical bench errors 15DIN ISO 11421:2010-10 E Reference straightedge or flat F Focal slide 0 Image analyser slideway P Fixture for test specimen ID Distance transducer II Indicator Figure 3 - Straightness and parallelism using distance transducer 5.12 Parallelism of surfaces and/or perpendicularity to reference axes An autocollimating telescope in conjunction with suitable plane mirrors can be used for checking that surfaces are parallel to each other. The same telescope (if suitably adjusted so that i
