1、BRITISH STANDARDBS ISO 517:2008Photography Apertures and related properties pertaining to photographic lenses Designations and measurementsICS 37.040.10g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g4
2、0g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS ISO 517:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 June 2008 BSI 2008ISBN 978 0 580 61341 8National forewordThis British Standard is the UK implementation of ISO 517:2008.The
3、UK participation in its preparation was entrusted by Technical Committee CPW/172, Optics and photonics, to Subcommittee CPW/172/1, Fundamental standards.A list of organizations represented on this subcommittee can be obtained on request to its secretary.This publication does not purport to include a
4、ll the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsReference numberISO 517:2008(E)INTERNATIONAL STANDARD ISO517Third e
5、dition2008-03-15Photography Apertures and related properties pertaining to photographic lenses Designations and measurements Photographie Ouvertures et grandeurs associes relatives aux objectifs photographiques Dsignations et mesurages BS ISO 517:2008ii iiiForeword ISO (the International Organizatio
6、n for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has
7、 the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Inter
8、national Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publicat
9、ion as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent righ
10、ts. ISO 517 was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 1, Fundamental standards. This third edition cancels and replaces the second edition (ISO 517:1996) which has undergone minor technical revision. BS ISO 517:2008blank1Photography Apertures and related p
11、roperties pertaining to photographic lenses Designations and measurements 1 Scope This International Standard pertains to apertures and related properties of photographic lenses affecting the illuminance at the centre of the image. This International Standard specifies aperture markings for all type
12、s of lenses used in still cameras, and gives tolerances for the stop numbers. It also defines aperture stop, entrance pupil, focal length, relative aperture and stop numbers, and gives methods for their measurement or determination. This International Standard applies only to lenses focused on objec
13、ts at infinity; that is, at least 50 times the focal length of the lens. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 aperture stop physical stop that limits the cross-section of the light beam that can pass through the lens to reach the c
14、entre of the on-axis image 2.2 entrance pupil image of the aperture stop as viewed from a point in the object space on its optical axis (the image of the aperture stop formed by the front elements of the lens) 2.3 exit pupil image of the aperture stop as viewed from a point in the image plane of the
15、 lens and on its optical axis (the image of the aperture stop formed by the rear elements of the lens) 2.4 focal length of the photographic lens f limiting value of the image size h of a sharp imaged far-distant object h divided by its angular extension in the object space i.e. lim0tan( )hf=See Figu
16、re 1. 2.5 relative aperture of a photographic lens twice the numerical aperture where the numerical aperture is the sine of the semi-angle subtended by the exit pupil at the focal plane NOTE For photographic applications, the relative aperture is equivalent (within a 1/3 stop) to the ratio of the di
17、ameter of the entrance pupil to the focal length. BS ISO 517:20082 2.6 f-number stop number the reciprocal value of the relative aperture (2.5) 2.7 true f-number unrounded standard f-number See 3.2.2. Key 1 lens under test NOTE The object size h is positive, the image size h is negative and is posit
18、ive. Figure 1 Focal length of a photographic lens (2.4) 3 Aperture markings 3.1 Designations The relative aperture of a lens shall be designated by 1: followed by the numerical value of f-number, for example 1:2,8. Where preferable, the symbol f/ followed by the number value may be used, for example
19、 f/2,8. 3.2 Marking series 3.2.1 Standard series of f-number marking The standard series of f-number marking shall be as follows: 0,5 0,7 1 (or 1,0) 1,4 2 2,8 4 5,6 8 11 16 22 32 45 64 90 128. NOTE When f-numbers are marked on a lens, points may be used as decimal signs instead of commas. 3.2.2 Stan
20、dard f-number series The standard f-number, or “whole stop” series shall be calculated according to the following formula: 2-number 2mf = where m = 2, 1, 0, 1, 2, . (m is an integer). BS ISO 517:200833.2.3 f-number of the maximum relative aperture The f-number of the maximum relative aperture, that
21、is the smallest f-number pertaining to the given lens, need not be selected from the standard series, but shall be followed by the series, beginning with the next larger number whenever practical, and progressing as far as required in the individual application. EXAMPLE A 1:1,9 lens could be marked
22、1,9 2,8 4 5,6 8 etc., if it were believed that to mark it 1,9 2,0 2,8 4,0 5,6 etc., would confuse the markings at the 1,9 end of the scale. 3.2.4 Subdivisions of the standard f-number Each standard f-number, or “whole stop”, division of scale markings may be divided into two or three subdivisions in
23、 1/2 or 1/3 steps of a stop calculated, for 1/2 subdivision, in a geometric series with first term 0,5 and factor 42 and for 1/3 subdivision in a geometric series with first term 0,5 and factor 62 . Table 1 gives the calculated whole, half and third stops. Table 1 f-number series Whole stop Half sto
24、p Third stop Whole stop Half stop Third stop 0,500 0,500 0,500 0,595 0,561 22,63 22,63 22,63 0,707 0,630 26,91 25,40 0,707 0,841 0,707 32,00 28,51 1,000 0,794 32,00 38,05 32,00 1,189 0,891 45,25 35,92 1,000 1,414 1,000 53,82 40,32 1,682 1,122 45,25 64,00 45,25 2,000 1,260 76,11 50,80 1,414 2,378 1,4
25、14 90,51 57,02 2,828 1,587 64,00 107,6 64,00 3,364 1,782 128,0 71,84 2,000 4,000 2,000 80,63 4,757 2,245 90,51 90,51 5,657 2,520 101,6 2,828 6,727 2,828 114,0 8,000 3,175 128,0 128,0 9,514 3,564 4,000 11,31 4,000 13,45 4,490 16,00 5,040 5,657 19,03 5,657 6,350 7,127 8,000 8,000 8,980 10,08 11,31 11,
26、31 12,70 14,25 16,00 16,00 17,96 20,16 BS ISO 517:20084 4 Tolerances of f-numbers for photographic lenses The measured f-numbers shall equal the true f-number within the tolerances given in Table 2. If the full aperture f-number is selected from the standard series, the tolerance shall be applied to
27、 the true f-number. Table 2 Tolerances of measured f-numbers Marked f-number Tolerances (to true f-number) Full aperture 5 % Smaller than f/5,6 + 12 % 11 % ( 1/3 stop) f/5,6 and larger + 19 % 16 % ( 1/2 stop) 5 Methods for measuring effective entrance pupil and focal length 5.1 General There are a n
28、umber of possible procedures for measuring the effective entrance pupil and focal length of a photographic lens, which may be used if the measuring errors are within the permissible tolerances. As examples, two of the methods most frequently used for measuring the entrance pupil and two methods for
29、measuring the focal length are given in 5.2. NOTE These measurement methods are appropriate for lenses of focal lengths from 20 mm to 500 mm and with apertures from 5 mm to 100 mm. For lenses outside this range, other methods might be appropriate. 5.2 Measurement methods 5.2.1 Effective entrance pup
30、il 5.2.1.1 Method 1 for measuring the diameter of the effective pupil of a photographic lens 5.2.1.1.1 Principle Method 1 uses a direct measurement of the entrance pupil diameter. 5.2.1.1.2 Apparatus 5.2.1.1.2.1 Travelling compound microscope, with means for shifting the microscope in a direction at
31、 right angles to its axis through a measured distance not less than the diameter of the effective entrance pupil to be measured. The microscope shall have a working distance sufficiently long to permit the microscope to be focused on the limiting opening of the photographic lens through its front el
32、ement, and shall be fitted with a reticle. 5.2.1.1.2.2 Extended light source. 5.2.1.1.3 Procedure Mount the photographic lens, the effective entrance pupil of which is to be measured, with its axis parallel to the axis of the measuring microscope (5.2.1.1.2.1). Illuminate the lens using the extended
33、 light source (5.2.1.1.2.2) through its rear element and direct the front element of the lens towards the measuring microscope. Focus the microscope upon the edge of the opening with the smallest apparent diameter. The microscope is then traversed. By measuring its displacement, determine the diamet
34、er of this opening, which is the effective entrance pupil. If the opening is not circular, the diameter of a circle with the same area as that of the actual entrance pupil shall be used. BS ISO 517:200855.2.1.2 Method 2 for measuring the diameter of the effective entrance pupil of a photographic len
35、s 5.2.1.2.1 Principle Method 2 uses the telecentric projection system method. 5.2.1.2.2 Apparatus 5.2.1.2.2.1 Telecentric projection system, (hereafter referred to as “projection system”) consisting of a projection lens; a telecentric aperture stop; a screen. The projection system shall be aligned a
36、s shown in Figure 2. 5.2.1.2.2.2 Extended light source. 5.2.1.2.3 Procedure 5.2.1.2.3.1 Place the lens under test between the extended light source (5.2.1.2.2.2) and the projection system (5.2.1.2.2.1). The image side of the lens shall face the extended light source, with the optical axis of the len
37、s coinciding with that of the projection system. 5.2.1.2.3.2 Move the lens under test along the optical axis of the projection system so as to obtain the sharpest image of the entrance pupil of the lens on the screen. Measure the area or diameter of the image. In doing this, the diameter of the tele
38、centric aperture is adjusted so that the edge of the apertures image A (see Figure 2) is sharp enough for accurate measurement. Key 1 extended light source 2 lens under test 3 projection lens 4 telecentric projection system 5 telecentric aperture stop 6 screen 7 image of the entrance pupil A area, i
39、n square millimetres, of the image of the entrance pupil Figure 2 Schematic layout of telecentric projection system apparatus (see 5.2.1.2.2) BS ISO 517:20086 5.2.1.2.3.3 Calibrate the lateral magnification of the projection system in the following manner. Replace the lens by an object of known area
40、 or diameter, the shape and dimensions of which shall be approximately the same as those of the entrance pupil of the lens during normal use. Project the image of the known object on the screen and measure the projected area or diameter. In measuring the area or diameter of the known object, the dia
41、meter of the telecentric aperture stop shall be the same as in 5.2.1.2.3.2. Determine the magnification by taking the ratio of the dimensions of the image to those of the known object. 5.2.1.2.4 Diameter of the relative aperture Calculate this using the following equation: 21,13AdAmm= where d is the
42、 diameter, in millimetres, of the effective entrance pupil used to calculate the relative aperture; A is the area, in square millimetres, of the image of the entrance pupil (see Figure 2); m is the magnification of the projection system. NOTE If the shape of the lens aperture is circular, or can be
43、regarded as a circle, the diameter of the relative aperture can be obtained from the following equation: ddm= where d is the diameter, in millimetres, of the image of the entrance pupil. 5.2.2 Focal length 5.2.2.1 Method 1 for measuring the focal length of a photographic lens 5.2.2.1.1 Principle Met
44、hod 1 for measuring the focal length of a photographic lens uses the formula given in 2.4. 5.2.2.1.2 Apparatus 5.2.2.1.2.1 Telescope fitted with a reticle, and of focal length suitable for observing the image at infinity of each graduation of the scale. The telescope shall be able to pivot approxima
45、tely around the centre of the first nodal point of the test lens by an amount equal to or greater than the angle (see 2.4 and Figure 3). The aberrations of the telescope shall be small enough to not affect the measured values. The diameter of the telescope shall be greater than that of the entrance
46、pupil of the lens to be tested. 5.2.2.1.2.2 Extended monochromatic light source, of wavelength = 546 nm (green mercury line). 5.2.2.1.2.3 Engraved scale. BS ISO 517:20087Key 1 scale illuminated with light of wavelength = 546 nm 2 lens under test 3 first nodal point 4 teleoptics Figure 3 Schematic la
47、yout of apparatus for measuring the focal length (Method 1) (see 5.2.2.1) 5.2.2.1.3 Procedure Place the engraved scale (5.2.2.1.2.3) with engraving h in the second focal plane of the test lens and illuminate it with the extended light source (5.2.2.1.2.2). If possible, focus the lens and measure the
48、 focal length at an aperture of f/5,6. Otherwise carry out the measurement at full aperture. Pivot the telescope (5.2.2.1.2.1) in such a way that the image of the graduations of the scale is aligned with the centre of the reticle and record the corresponding angle . In order to avoid measuring error
49、s due to distortion, measure the relation (see 2.4)tan( )hfor several values of image heights h and corresponding angles to evaluate the limiting value 0. 5.2.2.2 Method 2 for measuring the focal length of a photographic lens 5.2.2.2.1 Apparatus 5.2.2.2.1.1 Collimator, of known focal length with target of known size in its focal plane, the size of the target not being more than 1/50 of the focal length of the collimator. The focal length of the collimator
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