ISO 21395-2:2022

INTERNATIONAL ISO
STANDARD 21395-2
First edition
2022-02
Optics and photonics — Test method
for refractive index of optical
glasses —
Part 2:
V-block refractometer method
Optique et photonique — Méthode d'essai pour l'indice de réfraction
des verres optiques —
Partie 2: Méthode du réfractomètre à blocs en V
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 2
5 Measuring equipment . 3
5.1 General . 3
5.2 Light source . 4
5.3 Bandpass filter . 5
5.4 Slit . 5
5.5 Collimator lens . 5
5.6 V-block prism . 5
5.7 Origin-point reference block . 6
5.8 Telescope . 6
5.9 Detector . 7
5.10 Deviation-angle measuring device . 7
5.11 Refractive index matching liquid . 7
6 Shapes of origin-point reference block and specimen . 7
6.1 General . 7
6.2 Apex angle. 7
6.3 Contact face with V-block prism . 7
7 Measurement method . 8
7.1 Measurement environment . 8
7.1.1 Temperature . 8
7.1.2 Atmospheric pressure . 8
7.2 Measurement . 8
7.2.1 General . 8
7.2.2 Preparation for measurement . 8
7.2.3 Setting of deviation-angle origin point (0°) . 8
7.2.4 Adjustment of V-block prism . 9
7.2.5 Measurement of deviation angle . 9
7.2.6 Calculation of refractive index . 10
8 Indication .10
9 Test report .10
Annex A (normative) Refractive index matching liquid .12
Annex B (informative) Telescope with autocollimation function .14
Annex C (normative) Alternative measurement .15
Annex D (normative) Measurement with reference specimen.24
Bibliography .26
iii
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
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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).
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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
Introduction
This document specifies the method to determine the refractive index of optical glasses with the
V-block refractometer. Some explanation of the V-block refractometer can be found in Reference [3].
The refractive index of optical glasses is the most important characteristic for the optical elements
manufactured from them.
Regarding the standardization of the method of refractive index measuring method of optical glasses,
the minimum deviation method is defined as ISO 21395-1.
The minimum deviation method is most accurate in refractive index measurement but requires an
advanced technical skill to prepare a specimen with a precise shape and to measure the refractive index.
In contrast the V-block refractometer method is easier and faster when preparing a specimen and
requires less technical skill for measurement. Therefore, this method is commonly used by people
checking the quality of the optical glass products on a daily basis.
This document is intended to aid in measuring the refractive index of optical glasses accurately and
improving the communications between raw optical glass suppliers and optical element manufacturers
as well.
v
INTERNATIONAL STANDARD ISO 21395-2:2022(E)
Optics and photonics — Test method for refractive index of
optical glasses —
Part 2:
V-block refractometer method
1 Scope
This document specifies a method to determine the refractive index of optical glass with the accuracy
-5
within 3 × 10 at the wavelength range from 365 nm to 2 400 nm by using the V-block refractometer
method.
While this document can be used for non-glass materials, the user is informed that only optical glass
has been considered in the development of this document, and other materials can have issues, which
have not been taken into consideration.
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.
ISO 280, Essential oils — Determination of refractive index
ISO 9802, Raw optical glass — Vocabulary
ISO 21395-1, Optics and photonics — Test method for refractive index of optical glasses — Part 1: Minimum
deviation method
ISO 80000-1, Quantities and units — Part 1: General
ISO 80000-3, Quantities and units — Part 3: Space and time
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9802, ISO 80000-1,
ISO 80000-3 and the following apply.
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 https:// www .electropedia .org/
3.1
V-block prism
prism manufactured from optical glass material with a known refractive index
3.2
refractive index matching liquid
transparent liquid having the refractive index close to that of the specimen
4 Principles
As shown in Figure 1 a), when a beam aligned perpendicular to the entrance face transmits through
the V-block
...