ISO 21395-1:2020
(Main)Optics and photonics — Test method for refractive index of optical glasses — Part 1: Minimum deviation method
Optics and photonics — Test method for refractive index of optical glasses — Part 1: Minimum deviation method
This document specifies the measuring method for the refractive index of optical glasses with the accuracy within 1 × 10−5 used in the spectral range from 365 nm to 2 400 nm. Additional information on how to apply the refractive index in the dispersion and the various dispersion formulae of optical glasses is given in Annex A and Annex B.
Optique et photonique — Méthode d’essai pour déterminer l’indice de réfraction des verres optiques — Partie 1: Méthode de la déviation minimale
General Information
Buy Standard
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21395-1
First edition
2020-06
Optics and photonics — Test method
for refractive index of optical
glasses —
Part 1:
Minimum deviation method
Optique et photonique — Méthode d’essai pour déterminer l’indice de
réfraction des verres optiques —
Partie 1: Méthode de la déviation minimale
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Measuring apparatus . 2
5.1 General construction . 2
5.2 Goniometer. 3
5.3 Light source . 3
5.4 Detector . 4
6 Specimen prism . 4
6.1 General . 4
6.2 Dimensions . 5
6.3 Apex angle . 5
6.4 Flatness . 5
7 Environmental condition of measurement . 5
7.1 Temperature . 5
7.2 Humidity . 5
7.3 Atmospheric pressure. 5
8 Measurement . 6
8.1 Adjustment of the measurement specimen prism . 6
8.2 Measurement of the apex angle, α . 6
8.3 Measurement of the angle of minimum deviation, δ . 7
min
9 Indication . 8
10 Test report . 8
Annex A (informative) Calculation of principal dispersion, Abbe number, partial dispersion
and relative partial dispersion . 9
Annex B (informative) Dispersion formulae for calculation of refractive index at arbitrary
wavelength .12
Annex C (informative) Correction of refractive index for temperature, humidity and
atmospheric pressure .14
Annex D (informative) Other measurement methods of the apex angle .16
Annex E (informative) Other measurement methods of the angle of minimum deviation .18
Bibliography .21
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 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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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 rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 3, Optical materials and components.
A list of all parts in the ISO 21395 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
Introduction
The refractive index of optical glasses has been measured by various methods, but up to now, an
International Standard for the measurement has not been available. The refractive index of optical
glasses is the most important characteristic for the optical elements to be manufactured from
them. This document defines a suitable method for measuring the refractive index of optical glasses
accurately and also helps to improve communication between raw optical glass suppliers and optical
element manufacturers.
INTERNATIONAL STANDARD ISO 21395-1:2020(E)
Optics and photonics — Test method for refractive index of
optical glasses —
Part 1:
Minimum deviation method
1 Scope
This document specifies the measuring method for the refractive index of optical glasses with the
−5
accuracy within 1 × 10 used in the spectral range from 365 nm to 2 400 nm.
Additional information on how to apply the refractive index in the dispersion and the various dispersion
formulae of optical glasses is given in Annex A and Annex B.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses.
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle
As shown in Figure 1, when the monochromatic light beam is refracted by the specimen prism at
the angle of minimum deviation, the relative refractive index of the specimen prism to the air at the
wavelength of the monochromatic light beam is described by the following Formula (1):
αδ+
min
sin
n = (1)
rel
α
sin
where
n is the relative refractive index (n = n /n );
rel rel abs air
n is the absolute refractive index of the specimen prism;
abs
n is the refractive index of air;
air
α is the apex angle;
δ is the angle of minimum deviation.
min
As shown in Figure 1, light enters the plane AB of the specimen prism at an angle of incidence (θ) and
exits from the plane AC at an exit angle (θ′). The incident and the exiting light ray form the deviation
angle (δ). With the deviation angle minimized, the incident and the exiting angles are equal. The smallest
angle of deviation is called the angle of minimum deviation. The angle of minimum deviation (δ ) and
min
the apex angle (α) of the specimen prism are measured, and the refractive index is calculated using
those angles. Formulae for the calculation of principal dispersion, Abbe number, partial dispersion and
relative partial dispersion are given in Annex A. The dispersion formulae that calculate the refractive
index at the wavelength different from the measured wavelengths are given in Annex B. The correction
of the refractive index of optical glasses for temperature, humidity and atmospheric pressure of optical
glasses are given in Annex C.
NOTE When measuring the refractive index with this method, it is necessary to consider temperature,
pressure, humidity and measurement errors. Expressions for the relations of these errors are described
in ISO 17328. The dependence of the refractive index of air on temperature and pressure can be found in
ISO 12123:2018, A.3.
Key
θ angle of incidence δ angle of minimum deviation
min
θ′ exit angle 1 incident light
α apex angle 2 transmitted light
A, B, C the vertices of the prism 3 minimum deviation
Figure 1 — Principle of minimum deviation method
5 Measuring apparatus
5.1 General construction
The measuring apparatus is shown in Figure 2.
2 © ISO 2020 – All rights reserved
Key
1 light source 4 rotating stage coupled with prism (5)
2 collimator 5 specimen prism
3 goniometer coupled with telescope (6) 6 telescope
and detector (7) 7 detector
Figure 2 — Schematic of minimum deviation metho
...
INTERNATIONAL ISO
STANDARD 21395-1
First edition
2020-06
Optics and photonics — Test method
for refractive index of optical
glasses —
Part 1:
Minimum deviation method
Optique et photonique — Méthode d’essai pour déterminer l’indice de
réfraction des verres optiques —
Partie 1: Méthode de la déviation minimale
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Measuring apparatus . 2
5.1 General construction . 2
5.2 Goniometer. 3
5.3 Light source . 3
5.4 Detector . 4
6 Specimen prism . 4
6.1 General . 4
6.2 Dimensions . 5
6.3 Apex angle . 5
6.4 Flatness . 5
7 Environmental condition of measurement . 5
7.1 Temperature . 5
7.2 Humidity . 5
7.3 Atmospheric pressure. 5
8 Measurement . 6
8.1 Adjustment of the measurement specimen prism . 6
8.2 Measurement of the apex angle, α . 6
8.3 Measurement of the angle of minimum deviation, δ . 7
min
9 Indication . 8
10 Test report . 8
Annex A (informative) Calculation of principal dispersion, Abbe number, partial dispersion
and relative partial dispersion . 9
Annex B (informative) Dispersion formulae for calculation of refractive index at arbitrary
wavelength .12
Annex C (informative) Correction of refractive index for temperature, humidity and
atmospheric pressure .14
Annex D (informative) Other measurement methods of the apex angle .16
Annex E (informative) Other measurement methods of the angle of minimum deviation .18
Bibliography .21
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 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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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 rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 3, Optical materials and components.
A list of all parts in the ISO 21395 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
Introduction
The refractive index of optical glasses has been measured by various methods, but up to now, an
International Standard for the measurement has not been available. The refractive index of optical
glasses is the most important characteristic for the optical elements to be manufactured from
them. This document defines a suitable method for measuring the refractive index of optical glasses
accurately and also helps to improve communication between raw optical glass suppliers and optical
element manufacturers.
INTERNATIONAL STANDARD ISO 21395-1:2020(E)
Optics and photonics — Test method for refractive index of
optical glasses —
Part 1:
Minimum deviation method
1 Scope
This document specifies the measuring method for the refractive index of optical glasses with the
−5
accuracy within 1 × 10 used in the spectral range from 365 nm to 2 400 nm.
Additional information on how to apply the refractive index in the dispersion and the various dispersion
formulae of optical glasses is given in Annex A and Annex B.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses.
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Principle
As shown in Figure 1, when the monochromatic light beam is refracted by the specimen prism at
the angle of minimum deviation, the relative refractive index of the specimen prism to the air at the
wavelength of the monochromatic light beam is described by the following Formula (1):
αδ+
min
sin
n = (1)
rel
α
sin
where
n is the relative refractive index (n = n /n );
rel rel abs air
n is the absolute refractive index of the specimen prism;
abs
n is the refractive index of air;
air
α is the apex angle;
δ is the angle of minimum deviation.
min
As shown in Figure 1, light enters the plane AB of the specimen prism at an angle of incidence (θ) and
exits from the plane AC at an exit angle (θ′). The incident and the exiting light ray form the deviation
angle (δ). With the deviation angle minimized, the incident and the exiting angles are equal. The smallest
angle of deviation is called the angle of minimum deviation. The angle of minimum deviation (δ ) and
min
the apex angle (α) of the specimen prism are measured, and the refractive index is calculated using
those angles. Formulae for the calculation of principal dispersion, Abbe number, partial dispersion and
relative partial dispersion are given in Annex A. The dispersion formulae that calculate the refractive
index at the wavelength different from the measured wavelengths are given in Annex B. The correction
of the refractive index of optical glasses for temperature, humidity and atmospheric pressure of optical
glasses are given in Annex C.
NOTE When measuring the refractive index with this method, it is necessary to consider temperature,
pressure, humidity and measurement errors. Expressions for the relations of these errors are described
in ISO 17328. The dependence of the refractive index of air on temperature and pressure can be found in
ISO 12123:2018, A.3.
Key
θ angle of incidence δ angle of minimum deviation
min
θ′ exit angle 1 incident light
α apex angle 2 transmitted light
A, B, C the vertices of the prism 3 minimum deviation
Figure 1 — Principle of minimum deviation method
5 Measuring apparatus
5.1 General construction
The measuring apparatus is shown in Figure 2.
2 © ISO 2020 – All rights reserved
Key
1 light source 4 rotating stage coupled with prism (5)
2 collimator 5 specimen prism
3 goniometer coupled with telescope (6) 6 telescope
and detector (7) 7 detector
Figure 2 — Schematic of minimum deviation metho
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.