ISO INTERNATIONAL STANDARD 7944 Second edition 1998-06-01 Optics and optical instruments - Reference wavelengths Optique et instruments d'optique - Longueurs d'onde de reférence ISO Reference number ISO 7944:1998(E) by IHS under lic Not for Resale ISO 7944:1998(E) Foreword IsO (the International Organization 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 liaison with isO, also take part in the work. IsO collaborates closely with the International Electrotechnical Commission(lEC)onallmattersofelectrotechnicalstandardization Draft International Standards adopted by the technical committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 7944 was prepared by Technical Committee ISO/TC 172, Optics and optical instruments. This second edition cancels and replaces the first edition (isO 7944:1984), which has been technically revised. @ISO1998 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic InternationalOrganizationforStandardization Casepostale56·CH-1211Geneve20·Switzerland Internet [email protected] Printed in Switzerland Not for Resale INTERNATIONAL STANDARD@ISO ISO 7944:1998(E) Optics and optical instruments Reference wavelengths 1 Scope This International Standard specifies two reference wavelengths to be used for the characterization of optical materials, optical systems and instruments, as well as ophthalmic lenses. It defines the associated principal refractive indices and principal dispersions, as well as the Abbe numbers with regard to these reference wavelengthsandprincipaldispersions. 2 Reference wavelengths, principal dispersions and Abbe numbers 2.1 General The reference wavelengths are the mercury e-line 546,07 nm (see 2.2) and the helium d-line 587,56 nm (see 2.3) For non-ophthalmic applications the mercury e-line shall be the reference wavelength. Other wavelengths which may be used in addition to these reference wavelengths are given in tables 1, 2 and 3. NOTE For the future, it is envisaged that only one reference wavelength is to be specified, even for ophthalmic use. 2.2 Mercury e-line 546,07 nm The associated principal refractive index n is the refractive index at the green mercury e-line and the associated principal dispersion is np: - Nc'; where is the refractive index at the blue cadmium F'-line; nc: is the refractive indexat the red cadmium C'-line. The Abbe number Ve with regard to this reference wavelength and this principal dispersion is defined as: ne-1 Ve Np. - nc 2.3 Helium d-line 587,56 nm principal dispersion is n - nc, where nF is the refractive index at the blue hydrogen F-line; al Organization for Standardizatior Not for Resale