1、May 2009DEUTSCHE NORM English price group 8No part of this standard 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).ICS 37.040.10!$Wf that is, at l
2、east 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 centre of the on-axis image 2.
3、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 lens and on its optical axis
4、 (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 Figure 1. 2.5 relative aperture o
5、f a photographic lens twice the numerical aperture where the numerical aperture is the sine of the semi-angle subtended by the exit NOTE For photographic applications, the relative aperture is equivalent (within a 1/3 stop) to the ratio of the diameter of the entrance pupil to the focal length. Phot
6、ography Apertures and related properties pertaining to photographic lenses Designations and measurements N1) National footnote: Applies to a magnification of zero. pupil at the focal plane N1)DIN ISO 517:2009-05 42.6 f-number stop number the reciprocal value of the relative aperture (2.5) 2.7 true f
7、-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 positive. 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: fol
8、lowed 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 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
9、 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 Standard 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,
10、0, 1, 2, . (m is an integer). DIN ISO 517:2009-05 53.2.3 f-number of the maximum relative aperture The f-number of the maximum relative aperture, that 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
11、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 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 Sub
12、divisions 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 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 geo
13、metric 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 stop 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,
14、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 1,414 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,
15、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 11,31 12,70 14,25 16,00 16,00 17,96 20,16 DIN ISO 517:2009-05 64 Tolerances of f-numbers for photographic lenses The measured f-numbers shall equal the
16、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 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 +
17、 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 number of possible procedures for measuring the effective entrance pupil and focal length of a photographic lens, which may be used if the measuri
18、ng errors are within the permissible tolerances. As examples, two of the methods most frequently used for measuring the entrance pupil and two methods for 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
19、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 pupil 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 measureme
20、nt 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 right angles to its axis through a measured distance not less than the diameter of the effective entrance pupil to be measured. The microscope s
21、hall have a working distance sufficiently long to permit the microscope to be focused on the limiting opening of the photographic lens through its front element, 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 entr
22、ance 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 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 microsc
23、ope upon the edge of the opening with the smallest apparent diameter. The microscope is then traversed. By measuring its displacement, determine the diameter 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
24、 the actual entrance pupil shall be used. DIN ISO 517:2009-05 75.2.1.2 Method 2 for measuring the diameter of the effective entrance pupil of a photographic lens 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,
25、 (hereafter referred to as “projection system”) consisting of a projection lens; a telecentric aperture stop; a screen. The projection system shall be aligned as 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
26、 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 lens 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
27、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 telecentric aperture is adjusted so that the edge of the apertures image A (see Figure 2) is sharp enough for accurate measurement. Key 1 extend
28、ed 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, in square millimetres, of the image of the entrance pupil Figure 2 Schematic layout of telecentric projection system apparatus (see 5.2.1.2.2
29、) DIN ISO 517:2009-05 85.2.1.2.3.3 Calibrate the lateral magnification of the projection system in the following manner. Replace the lens by an object of known area or diameter, the shape and dimensions of which shall be approximately the same as those of the entrance pupil of the lens during normal
30、 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 diameter 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 dimen
31、sions 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 diameter, in millimetres, of the effective entrance pupil used to calculate the relative aperture; A is the area, in square millimetres
32、, 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 regarded as a circle, the diameter of the relative aperture can be obtained from the following equation: ddm= where d is the diameter, i
33、n 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 Method 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 fit
34、ted 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 approximately 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).
35、 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 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.
36、3 Engraved scale. DIN ISO 517:2009-05 9Key 1 scale illuminated with light of wavelength = 546 nm 2 lens under test 3 first nodal point 4 teleoptics Figure 3 Schematic layout 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
37、) with engraving h in the second focalilluminate it with the extended light source (5.2.2.1.2.2). If possible, focus the lens and measure the 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
38、the graduations of the scale is aligned with the centre of the reticle and record the corresponding angle . In order to avoid measuring errors 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.
39、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
40、 shall be at least three times the focal length of the lens under test. The aberrations of the collimator shall be small enough to not affect the measured values. The diameter of the exit pupil of the collimator shall be much greater than that of the entrance pupil of the lens to be tested (see Figu
41、re 4). 5.2.2.2.1.2 Microscope, with total magnification of approximately 50. 5.2.2.2.1.3 Graduated scale, with an accuracy of 0,002 mm. 5.2.2.2.1.4 Extended monochromatic light source, of wavelength = 546 nm. N2) National footnote: As h relates to the second focal plane, this plane is on the image s
42、ide. plane of the test lens N2)and DIN ISO 517:2009-05 10Key 1 target h height of the target 2 collimator h height of the image of the target 3 aperture stop f0focal length of the collimator 4 lens under test f focal length of the lens under test 5 image of the target 6 screen 7 microscope Figure 4
43、Schematic layout of apparatus for measuring the focal length (Method 2) (see 5.2.2.2) 5.2.2.2.2 Procedure Place the lens under test facing the collimator (5.2.2.2.1.1) and, using the extended light source (5.2.2.2.1.4), produce the image of the target on the screen. The aperture of the lens shall be
44、 set to f/5,6 if the full aperture f-number is f/5,6 or smaller, otherwise carry out the measurement at full aperture. Measure the length of the image using the graduated scale (5.2.2.2.1.3) and calculate the focal length using the following equation: 0hffh= where f is the focal length of the lens under test; f0is the focal length of the collimator; h is the length of the target at the focal plane of the collimator; h is the length of the image of the target at the focal plane of the lens under test. DIN ISO 517:2009-05 11
