prEN ISO 25178-606

SLOVENSKI STANDARD
01-april-2025
Specifikacija geometrijskih veličin izdelka (GPS) - Tekstura površine: ploskovna -
606. del: Načrtovanje in značilnosti brezkontaktnih instrumentov (sprememba
ostrine) (ISO/DIS 25178-606:2025)
Geometrical product specifications (GPS) - Surface texture: Areal - Part 606: Design and
characteristics of non-contact (focus variation) instruments (ISO/DIS 25178-606:2025)
Geometrische Produktspezifikation (GPS) - Oberflächenbeschaffenheit: Flächenhaft -
Teil 606: Aufbau und Merkmale von berührungslos messenden Geräten (Fokusvariation)
(ISO/DIS 25178-606:2025)
Spécification géométrique des produits (GPS) - État de surface: Surfacique - Partie 606:
Conception et caractéristiques des instruments sans contact (à variation de focale)
(ISO/DIS 25178-606:2025)
Ta slovenski standard je istoveten z: prEN ISO 25178-606
ICS:
17.040.20 Lastnosti površin Properties of surfaces
17.040.40 Specifikacija geometrijskih Geometrical Product
veličin izdelka (GPS) Specification (GPS)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 25178-606
ISO/TC 213
Geometrical product specifications
Secretariat: BSI
(GPS) — Surface texture: Areal —
Voting begins on:
Part 606: 2025-02-17
Design and characteristics of
Voting terminates on:
2025-05-12
non-contact (focus variation)
instruments
ICS: 17.040.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 25178-606:2025(en)
DRAFT
ISO/DIS 25178-606:2025(en)
International
Standard
ISO/DIS 25178-606
ISO/TC 213
Geometrical product specifications
Secretariat: BSI
(GPS) — Surface texture: Areal —
Voting begins on:
Part 606:
Design and characteristics of
Voting terminates on:
non-contact (focus variation)
instruments
ICS: 17.040.40
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: +41 22 749 01 11
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 25178-606:2025(en)
ii
ISO/DIS 25178-606:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Instrument requirements . 5
5 Metrological characteristics . 6
6 Design features . 6
7 General information . 7
Annex A (informative) Components of a focus variation instrument . 8
Annex B (informative) Sources of measurement error for focus variation . 14
Annex C (informative) Relationship to the GPS matrix model . 17
Bibliography .18

iii
ISO/DIS 25178-606:2025(en)
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 213, Dimensional and geometrical product
specifications and verification.
This second edition cancels and replaces the first edition (ISO 25178:606:2015), which has been technically
revised.
The main changes are as follows:
— adoption of the new structure of the series ISO 25178-60x documents;
— extension to focus variation using fixed pattern illumination.
A list of all parts in the ISO 25178 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/DIS 25178-606:2025(en)
Introduction
This document is a geometrical product specification (GPS) standard and is to be regarded as a general GPS
standard (see ISO 14638). It influences the chain link F of the chain of standards on profile and areal surface
texture.
The ISO GPS matrix model given in ISO 14638 gives an overview of the ISO GPS system of which this
document is a part. The fundamental rules of ISO GPS given in ISO 8015 apply to this document and the
default decision rules given in ISO 14253-1 apply to specifications made in accordance with this document,
unless otherwise indicated.
For more detailed information of the relation of this document to other standards and the GPS matrix model,
see Annex C.
This document includes normative terms and definitions relevant to the focus variation method for the
measurement of areal surface topography. The informative Annex A briefly summarizes focus variation
measurement instruments and methods to clarify the normative definitions and to provide a foundation
for informative Annex B, which describes common sources of errors and their relation to the metrological
characteristics of focus variation.
NOTE Portions of this document, particularly the informative sections, describe patented systems and methods.
This information is provided only to assist users in understanding the operating principles of focus variation. This
document is not intended to establish priority for any intellectual property, nor does it imply a license to proprietary
technologies described herein.

v
DRAFT International Standard ISO/DIS 25178-606:2025(en)
Geometrical product specifications (GPS) — Surface
texture: Areal —
Part 606:
Design and characteristics of non-contact (focus variation)
instruments
1 Scope
This document specifies the design and characteristics of focus variation instruments for areal measurement
of surface topography. Because surface profiles can be extracted from areal surface topography data the
methods described in this document can be applied to profiling measurements as well.
This document deals with focus variation without pattern illumination or with fixed pattern illumination.
The methods using varying pattern illumination during the measurement are excluded from this document.
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 25178-600:2019, Geometrical product specifications (GPS) — Surface texture: Areal — Part 600:
Metrological characteristics for areal topography measuring methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
focus variation
FV
measurement method whereby the sharpness of a series of surface images that is acquired during an axial
scan in an optical instrument is used to measure the surface topography
Note 1 to entry: In this document, surface image is an image of a surface obtained by capturing the reflected light from
the surface with or without a fixed pattern illumination.
Note 2 to entry: In this document, sharpness is a quantity of the surface image calculated by the neighbourhood
information indicating best focus. Other names for sharpness are for example contrast.
Note 3 to entry: Focus variation without fixed pattern illumination only works on optically rough surfaces
[ISO 25178-600:2019, 3.4.5]. If fixed pattern illumination is used, optically smooth surfaces [ISO 25178-600:2019,
3.4.4] can also be measured.
ISO/DIS 25178-606:2025(en)
3.2
focus variation sensor
device that converts the height of points on the surface into signals during measurement using the focus
variation method
3.3
axial scan
mechanical or optical displacement between the sample under inspection and the imaging optics
Note 1 to entry: The optical axis of the imaging optics is nominally parallel to the axial scan axis of the microscope.
[SOURCE: ISO 25178-607:2019, 3.5, Note 1 to entry modified with "imaging optics" replaced by "optical axis
of the imaging optics".]
3.4
focus variation measurement algorithm
algorithm for analysing the variation of focus in order to calculate the scan positions where each point is
best in focus
3.5
focus information
measure to quantify the degree of focus based on image sharpness at a specific lateral position in the surface
image and at a specific axial scan (3.3) position
3.6
focus information curve
signal recorded for a specific lateral position of the surface image as a function of the axial scan (3.3) position
Note 1 to entry: See Figure 1.
Note 2 to entry: The surface is located at the axial scan (3.3) position of the maximum of the focus information curve
(see key c in Figure 1).
Note 3 to entry: To improve the resolution in axial scan (3.3) direction the maximum of a fitted curve can be used
instead of key c in Figure 1.
ISO/DIS 25178-606:2025(en)
Key
a axial scan position
b focus information
c highest focus information from the captured axial scan positions
Figure 1 — Focus information curve
3.7
focus variation illumination system
source of light with a predefined spectral and spatial distribution
Note 1 to entry: Possible light sources are coaxial illumination, ring light and external light sources.
Note 2 to entry: A variant of coaxial illumination is the use of a fixed pattern projected onto a sample surface. For
example, this pattern can be a chessboard.
3.8
angular range of illumination
α
angular range from which the specimen is illuminated
Note 1 to entry: See Figure 2.
Note 2 to entry: The angular range of illumination affects the maximum measurable slope on optically smooth
surfaces.
3.8.1
angular range of coaxial illumination
α
I
angular range from which the specimen is coaxially illuminated
Note 1 to entry: The value α can be influenced by the choice of the objective.
I
Note 2 to entry: The value α is often related to the angular range of detection, see Figure 3.
I
Note 3 to entry: In normal cases, the value α can be derived from the numerical aperture of the objective.
I
Note 4 to entry: When special illumination sources are used (ring light, external light sources, etc., see Figure 2) the
angular range of illumination (3.8) can be much larger than α .
I
ISO/DIS 25178-606:2025(en)
3.8.2
minimum incident angle of ring light illumination
β
Imin
minimum incident angle of ring light illumination from which the specimen is illuminated
3.8.3
maximum incident angle of ring light illumination
β
Imax
maximum incident angle of ring light illumination from which the specimen is illuminated
Key
L lens of optical system
RL ring light
α angular range of coaxial illumination
I
β minimum incident angle of ring light illumination
Imin
β maximum incident angle of ring light illumination
Imax
S specimen
Figure 2 — Angular range of illumination
3.9
angular range of detection
α
D
angular range of light rays that can be gathered by the objective
Note 1 to entry: See Figure 3.

ISO/DIS 25178-606:2025(en)
Key
L lens of optical system
RL ring light
α angular range of detection
D
S specimen
Figure 3 — Angular range of detection
3.10
axial scan length
total range travelled by the focus variation microscope axial scan, usually the total displacement between
the sample and the microscope’s objective translated along its optical axis during data acquisition
Note 1 to entry: This parameter might be limited by the overall range of the axial scanner, but is generally a parameter
chosen by the operator taking account of the height range of the surface topography.
[SOURCE: ISO 25178-607:2019, 3.6, modified with "confocal microscope axial scan" replaced by "focus
variation microscope axial scan".]
3.11
polarization
method which allows one to filter out light waves in certain polarization states by using special optical
elements called polarizers (3.13) or analysers (3.12)
3.12
analyser
optical element used to polarize the rays of the light after they have been reflected from the specimen and
gathered by the objective
3.13
polarizer
optical element used to polarize the rays of the light source before they are transmitted to the specimen
4 Instrument requirements
An instrument according to this document shall perform areal surface topography measurements of a
sample surface using focus variation. The instrument shall comprise a focus variation sensor, optics, focus
variation illumination system, and an axial scanner. The instrument shall acquire data by illuminating the
surface with an angular range of illumination and capturing data from angular range of detection at several
axial positions along the optical axis by performing an axial scan over an axial scan length. To improve the
performance of specular reflection the use of polarization can help. Therefore, a polarizer and an analyser

ISO/DIS 25178-606:2025(en)
are used. The instrument shall convert acquired data to an areal topography using a focus variation
measurement algorithm which calculates the focus information to get the focus information curve.
Figure 4 shows the information flow between these elements for a FV instrument, from the real surface
to a scale limited surface. Example FV hardware, techniques and error sources are given in Annex A and
Annex B.
Key
measurand
operator with intended modification
operator without intended modification
Figure 4 — Information flow diagram
5 Metrological characteristics
The standard metrological characteristics for areal surface texture measuring instruments are listed and
explained in ISO 25178-600 and shall be considered when designing and calibrating the instrument.
Annex B describes error sources that might influence the calibration result.
6 Design features
Standard design features according to ISO 25178-600 shall be considered in the design.
Annex A provides examples of specific design features of FV instruments.

ISO/DIS 25178-606:2025(en)
7 General information
The relation between this document and the GPS matrix model is given in Annex C.

ISO/DIS 25178-606:2025(en)
Annex A
(informative)
Components of a focus variation instrument
A.1 Introduction
This Annex is a short overview of the focus variation principle and the components of a focus variation
instrument. Further literature can be found in references [11] [27].
A.2 Typical configuration
Figure A.1 illustrates the typical configuration of a focus variation instrument.
Key
1 array detector 8 focus information curve
2 optical components 9 light beam
3 white light source 10 analyser
4 illumination beam splitter 11 polarizer
5 objective 12 optical axis (.-.-.)
6 specimen 13 ring light (optional)
7 axial scan (along optical axis) 14 illumination pattern (optional)
Figure A.1 — Schematic diagram of a typical measurement instrument based on focus variation

ISO/DIS 25178-606:2025(en)
A.3 Operation principle
Focus variation combines the small depth of focus of an optical system with axial scanning along the optical
axis to provide topographical information from the variation of focus. In the following, the operating
principle is demonstrated for a typical focus variation instrument schematically shown in Figure A.1. The
main component of the system is the optical instrument containing various lenses that can be equipped
with different objectives allowing measurements with different resolution. With a beam splitting mirror,
light emerging from a white light source is inserted into the optical path of the system and focused onto the
specimen through the objective. Depending on the topography of the specimen, the light is scattered into
several directions as soon as it hits the specimen through the objective. If the topography shows diffuse
reflective properties, the light is scattered strongly into all directions. In the case of specular reflection, the
light is reflected mainly into one direction. All rays emerging from the spec
...