1、 Reference number ISO 1230:2007(E) ISO 2007INTERNATIONAL STANDARD ISO 1230 Third edition 2007-09-01 Photography Determination of flash guide numbers for electronic flash equipment Photographie Dtermination des nombres guides des appareils clairs ISO 1230:2007(E) PDF disclaimer This PDF file may cont
2、ain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibi
3、lity of not infringing Adobes licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation par
4、ameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2007 All r
5、ights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of
6、the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO 1230:2007(E) ISO 2007 All rights reserved iii Foreword ISO (the International Organiz
7、ation 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
8、 has 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. I
9、nternational 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. Publ
10、ication 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
11、rights. ISO 1230 was prepared by Technical Committee ISO/TC 42, Photography. This third edition cancels and replaces the second edition (ISO 1230:1992), which has been technically revised. ISO 1230:2007(E) iv ISO 2007 All rights reservedIntroduction In general flash photography, where the flash ligh
12、t source is mounted on a camera, the product of the camera lens -number and the distance from the flash light source to the subject is a constant with respect to the ISO speed of the film or the digital still camera to be used. The illuminance of the subject varies with the distance according to the
13、 inverse-square law and, in order to obtain the same suitable exposure on film or image sensor, the -number is adjusted with respect to the square root of the illuminance of the subject. The constant is named “flash guide number” and is a very useful guide for flash photographers, because the guide
14、number represents, in a sense, the power of illumination of the light source, for both flash lamps with and without integral reflectors and electronic flash equipment. The camera lens -number setting can easily be calculated by dividing the guide number by the distance from the flash light source to
15、 the subject. INTERNATIONAL STANDARD ISO 1230:2007(E) ISO 2007 All rights reserved 1 Photography Determination of flash guide numbers for electronic flash equipment 1 Scope This International Standard specifies the definition and determination of the ISO guide number of electronic flash equipment. I
16、t does not specify the definitions and measuring methods for the light output of electronic flash equipment, which are specified in ISO 2827. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 guide number N GNproduct of the camera lens -number,
17、 required for a suitable exposure on a film or an image sensor, and the distance from the flash light source to the subject with respect to the ISO speed of the film or the digital still camera to be used NOTE The guide number is expressed in metres. Annex A provides the conversion calculation for c
18、onverting the guide number from metres into feet. 2.2 ISO guide number N ISO/GNguide number, for a film or a digital still camera of ISO 100, “X ” synchronization and an exposure time which can fully utilize the total output of the flash light source 3 Calculation of the guide number 3.1 ISO guide n
19、umber The ISO guide number, N ISO/GN , shall be calculated using the following formula: ISO/GN ()d Nk I t t = (1) where k is a constant equal to 0,51 lm 1 m 2 s 1 ; I(t)dt is the time integral of the luminous intensity of electronic flash equipment, expressed in candella seconds (cd s = lm sr 1 s).
20、See Annex B for details of Equation (1). ISO 1230:2007(E) 2 ISO 2007 All rights reserved3.2 Guide number for any ISO speed other than 100 The guide number for any ISO speed other than 100 can be calculated from the following formula: (ISO, ) ISO/GN100 S S NN = (2) where S is the ISO speed (arithmeti
21、c). 4 Designation of guide number Designation of guide numbers on products or instructions should be rounded to two significant digits and followed by metres. When a guide number does not express the ISO guide number i.e. for films or digital still cameras other than those of ISO speed 100 (arithmet
22、ic), the reference ISO speed should follow in parentheses. EXAMPLES N ISO/GN20 m N GN40 m (ISO 400) ISO 1230:2007(E) ISO 2007 All rights reserved 3 Annex A (informative) Conversion calculation of the ISO guide number from metres into feet A.1 Conversion factor ISO guide numbers, expressed in feet, c
23、an be obtained from the metre guide numbers by multiplying by the factor 3,28. A.2 Designation of guide number in feet Designation of guide numbers on products or instructions should be rounded to the two significant digits and followed by feet. When a guide number does not express the ISO guide num
24、ber for films or digital still cameras other than ISO speed 100 (arithmetic), the reference ISO speed should follow in parentheses. EXAMPLES N ISO/GN20 m N ISO/GN 66 ft N GN40 m (ISO 400) N GN130 ft (ISO 400) ISO 1230:2007(E) 4 ISO 2007 All rights reservedAnnex B (informative) Explanation of guide n
25、umber formula B.1 Derivation of the numerical value The numerical value for k = 0,51 in Equation (1) was determined by combining all numerical values and constants in the guide number formula of ISO 1230:1973 as follows: GN 0,3 4 x NC I t S = (B.1) where N GNis the guide number, expressed in metres
26、(m); 0,3 is the metre-foot conversion factor (m ft 1 ); C is a constant and its numerical value is 0,004 5 (lm m 2 s 1 ); It is the effective luminous intensity, I, of the electronic flash equipment, expressed in candelas, multiplied by the effective exposure, t, expressed in seconds (cd s); S xis t
27、he arithmetic ISO film speed of x, and in this case, x is equal to 100. If It is substituted by I(t)dt, Equation (B.1) is equivalent to Equation (1) in 3.1. B.2 Derivation of ISO guide number formula This International Standard was based on the old ANSI PH2.4-1965 (which is now ANSI/NAPM IT2.24-1996
28、) and the procedure for the derivation of the guide number formula is as follows: The initial equation is based on the calibration equation for incident-light type exposure meters in ANSI PH2.12-1961 as follows: 2 CA t E S = (B.2) where E is the illuminance at the object plane, expressed in footcand
29、les (fc); t is the exposure time, expressed in seconds (s); A is the -number; S is the ASA (arithmetic ISO) film speed; C is a constant and its numerical value equal to 20,8 fc s to distinguish the constant C used in the old ANSI PH2.4-1965, with the constant C in the guide number equation given in
30、Equation (B.1), C is used here. ISO 1230:2007(E) ISO 2007 All rights reserved 5 According to ANSI PH2.12-1961, the numerical value of K for reflected-light type exposure meters is equal to 1,06 (cd ft 2 s). From the numerical values of K and C , the diffuse reflectance of the object, which is assume
31、d to be an isotropic diffuser (formerly called a uniform diffuser), can be calculated by the following equation: 1, 0 6 0,160 ( 16 %) 20,8 = (B.3) The equation for the illuminance with an accessory reflector is: 2 4 M E d = (B.4) where is the luminous flux, expressed in lumens (lm); M is the reflect
32、or factor; d is the distance, expressed in feet (ft), between a lamp and a subject. Combining Equations (B.2) and (B.4) gives: 22 4 A dC t M S = (B.5) Rearranging Equation (B.5) gives: 22 4 tMS Ad C = (B.6) GN 4 tMS AdN C = = (B.7) By substituting the numerical value of (3,14) and C (20,8), Equation
33、 (B.7) becomes: GN(ft) 0,003 8 Nt M S = (B.8) ANSI then rounded 0,003 8 (fc 1 s 1 ) to 0,004, which is the numerical value of C in the guide number formula, and corresponds with a reflectance of 16,7%. In the case of electronic flash equipment, the guide number formula is calculated by Equation (B.9
34、) if the relationship I = M/4 is taken into consideration: GN(ft) 0,004 4 NI t S = (B.9) In Equation (B.9), 0,004 is the rounded value of 0,003 8. Since 1 ft = 0,30 m (i.e. 0,304 8 m to be exact), the metre-guide number formula becomes: GN 0,3 0,004 4 NI t S = (B.10) Despite the fact that the calcul
35、ated value of C is 0,004, the value of 0,004 5 was adopted by TC 42 in the first edition of this International Standard (ISO 1230:1973) see Equation (B.1) to factor in the discrepancy between the numerical value of the guide number obtained according to the old ANSI PH2.4-1965 and that obtained acco
36、rding to the former German standard DIN 19011 (all parts) 13 14 15(June 1969 or January 1971 version). ISO 1230:2007(E) 6 ISO 2007 All rights reservedBibliography 1 ISO 6:1993, Photography Black-and-white pictorial still camera negative film/process systems Determination of ISO speed 2 ISO 516:1999,
37、 Photography Camera shutters Timing 3 ISO 517:1996, Photography Apertures and related properties pertaining to photographic lenses Designations and measurements 4 ISO 2240:2003, Photography Colour reversal camera films Determination of ISO speed 5 ISO 2721:1982, Photography Cameras Automatic control
38、s of exposure 6 ISO 2827:1988, Photography Electronic flash equipment Determination of light output and performance 7 ISO 5763:1989, Photography Electronic flash equipment Automatic control of exposure 8 ISO 5800:1987, Photography Colour negative films for still photography Determination of ISO spee
39、d 9 ISO 12232:2006, Photography Digital still cameras Determination of exposure index, ISO speed ratings, standard output sensitivity, and recommended exposure index 10 CIE Publication No.38-1977, Radiometric and photometric characteristics of materials and their measurement 11 ANSI PH2.4-1965 1) ,
40、Photography Materials for direct-positive colour print cameras Determination of ISO speed 12 ANSI PH2.12-1961, General-purpose photographic exposure meters (photoelectric type) 13 DIN 19011-1, Photoflash sources Determination of guide numbers and output data 14 DIN 19011-2, Photoflash sources Electr
41、onic flash equipment, automatic control of exposure 15 DIN 19011-3, Flashlight sources Identification numbers for spectral distribution of radiation 1) ANSI PH2.4-1965 has now been cancelled and replaced by ANSI/NAPM IT 2.24-1996. See http:/www.nssn.org. ISO 1230:2007(E) ICS 37.040.10 Price based on 6 pages ISO 2007 All rights reserved
