ISO/FDIS 12311
(Main)Personal protective equipment — Test methods for sunglasses and related eyewear
Personal protective equipment — Test methods for sunglasses and related eyewear
Équipement de protection individuelle — Méthodes d'essai pour lunettes de soleil et articles de lunetterie associés
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ISO/FDIS 12311:2023(E)
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ISO/TC 94/SC 6/WG 2 Style Definition: Heading 2: Font: Bold, Tab stops: Not
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Secretariat: BSI Style Definition: Heading 3: Font: Bold
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Date: 2023-07-27xx
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Personal protective equipment — Test methods for sunglasses and related
Style Definition: ANNEX
eyewear
Style Definition: TOC Heading
Équipement de protection individuelle — Méthodes d'essai pour lunettes de soleil et
Style Definition: AMEND Terms Heading: Font: Bold
articles de lunetterie associés
Style Definition: AMEND Heading 1 Unnumbered:
Font: Bold
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ISO/FDIS 12311:2023(E)
© ISO 2023
Formatted: Pattern: Clear
Formatted: Pattern: Clear
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.orgwww.iso.org
Published in Switzerland
ii © ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 12311:2023(E)
Contents
Foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Prerequisites. 5
5 General test requirements . 6
6 Test methods for mechanical properties . 6
6.1 Test method for frame deformation and filter retention . 6
6.1.1 Principle . 6
6.1.2 Apparatus . 6
6.1.3 Procedure . 7
6.1.4 Verification and test report . 8
6.1.5 Uncertainty of measurement . 9
6.2 Test method for increased endurance of sunglasses . 9
6.2.1 Principle . 9
6.2.2 Apparatus . 9
6.2.3 Procedure . 9
6.2.4 Verification and test report . 14
6.2.5 Uncertainty of measurement . 14
6.3 Test for resistance to perspiration of the sunglass frame . 14
6.3.1 Principle . 14
6.3.2 Apparatus and reagents . 14
6.3.3 Procedure . 15
6.3.4 Verification and test report . 16
Annex A (normative) Application of uncertainty of measurement . 17
Foreword iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
© ISO 2023 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 12311:2023(E)
4 Prerequisites . 2
5 General test requirements . 2
6 Test methods for mechanical properties . 2
6.1 Test method for frame deformation and filter retention . 2
6.1.1 Principle . 2
6.1.2 Apparatus . 2
6.1.3 Procedure . 3
6.1.4 Report . 4
6.1.5 Uncertainty of measurement . 5
6.2 Test method for increased endurance of sunglasses . 5
6.2.1 Principle . 5
6.2.2 Apparatus . 5
6.2.3 Procedure . 6
6.2.4 Report . 9
6.2.5 Uncertainty of measurement . 9
6.3 Test for resistance to perspiration of the sunglass frame . 9
6.3.1 Principle . 9
6.3.2 Apparatus and reagents . 9
6.3.3 Procedure . 10
6.3.4 Report . 11
Annex A (normative) Application of uncertainty of measurement . 12
Bibliography . 14
iv © ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 12311:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national
Formatted: Adjust space between Latin and Asian text,
standards bodies (ISO member bodies). The work of preparing International Standards is normally
Adjust space between Asian text and numbers
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 documentsdocument should be noted. This document was drafted in accordance
with the editorial rules of the ISO/IEC Directives, Part 2 (see
www.iso.org/directiveswww.iso.org/directives).
Attention is drawnISO draws attention to the possibility that some of the elementsimplementation of
this document may beinvolve the subjectuse 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. 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.htmlwww.iso.org/iso/foreword.html.
Formatted: English (United States)
This document was prepared by Technical Committee ISO/TC 94 Personal safety — Personal protective
equipment, Subcommittee SC 6 Eye and face protection, in collaboration with the European Committee
for Standardization (CEN) Technical Committee CEN/TC 85, Eye-protective equipment, in accordance
with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 12311:2013), which has been technically
Formatted: Pattern: Clear
revised.
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Formatted: Pattern: Clear
The main changes are as follows:
— with the publication of the four parts of ISO 18526 in 2020, which provides test methods and
Formatted: Pattern: Clear
specifications for head forms for the compliance testing of eye protectors, it was deemed
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unnecessary to reproduce details of these test methods in ISO 12311. They have therefore been
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removed. Test methods that have been retained in this document are those developed originally for
testing of spectacle frames. Corresponding Annexes that supplemented the now deleted test
Formatted: Pattern: Clear
methods have also been removed.
© ISO 2023 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/FDIS 12311:2023(E)
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.htmlwww.iso.org/members.html.
vi © ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 12311:2023(E)
Personal protective equipment — Test methods for sunglasses
and related eyewear
1 Scope
This document specifies reference's test methods for determining the properties of sunglasses given in
ISO 12312 (all parts). It is applicable to all sunglasses and related eyewear.
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Other test methods can be used if proven to be equivalent. Formatted: Pattern: Clear
Formatted: Pattern: Clear
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 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4007, Personal protective equipment — Eye and face protection — Vocabulary
ISO 8624, Ophthalmic optics — Spectacle frames — Measuring system and vocabulary
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4007, Personal protective equipment — Eye and face protection — Vocabulary
ISO 8624, Ophthalmic optics — Spectacle frames — Measuring system and vocabulary
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4007 and ISO 8624 apply.
Formatted: Pattern: Clear
ISO and IEC maintain terminological databases for use in standardization at the following addresses: Formatted: Pattern: Clear
— ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
© ISO 2023 – All rights reserved 1
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ISO/FDIS 12311:2023(E)
4 Prerequisites
The following parameters shall be specified prior to testing [see ISO 12312 (all parts)]:
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— the number of test samples; Formatted: Pattern: Clear
Formatted: Pattern: Clear
— test sample preparation;
— any conditioning prior to testing;
— characteristics to be assessed subjectively (if appropriate);
— pass/fail criteria.
5 General test requirements
Unless otherwise specified, the values stated in this document are expressed as nominal values. Except
for temperature limits, values which are not stated as maxima or minima shall be subject to a tolerance
of ±5 %. Unless otherwise specified, the ambient temperature for testing shall be between 16 °C and
32 °C. Where other temperature limits are specified, they shall be subject to an accuracy of ±2 °C.
Relative humidity shall be maintained at (50 ± 20) %.
Details of the material of reference test headforms to be used shall be as given in Annex B.
Unless otherwise specified, the filters shall be tested at the reference points as defined in ISO 4007.
Formatted: Pattern: Clear
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6 Test methods for mechanical properties
6.1 Test method for frame deformation and filter retention
6.1.1 Principle
This procedure tests the ability of the complete sunglass to resist deformation and to retain the filters.
6.1.2 Apparatus
6.1.2.1 Overall scheme, the test apparatus consists of an annular clamp, a downward-operating
pressure peg and a measuring device. See Figure 1.
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6.1.2.2 Annular clamp, (see Figure 1, key item 2) shall be capable of holding the test sample without
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twist or slip and have a diameter of (25 ± 2) mm, with two contact surfaces, E and E , made of a firm
1 2
elastic material (e.g. polyamide). The clamping surfaces shall be capable of being separated at least
10 mm on either side of a horizontal line going through the apparatus. To accommodate frames with a
significant face form angle, the annular clamp shall also be capable of rotating about a horizontal axis so
that the axis of the pressure peg (6.1.2.3) remains vertical and perpendicular to the plane of the
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unclamped lens at its boxed centre.
6.1.2.3 Pressure peg, (see Figure 1, key item 5) which operates vertically downwards shall have a
Formatted: Pattern: Clear
diameter of (10 ± 1) mm with a nominally hemispherical contact surface. The pressure peg shall be
capable of travelling from at least 10 mm above the horizontal line to not more than 8 mm below. The
horizontal distance between the annular clamp and pressure peg is adjustable. The pressure peg slides
in a guiding sleeve (See Figure 1, key item 4) that maintains its vertical orientation and lateral position.
Formatted: Pattern: Clear
2 © ISO 2023 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/FDIS 12311:2023(E)
6.1.2.4 Measuring device, to measure the linear displacement of the pressure peg, with an
uncertainty no greater than ±0,1 mm.
Linear dimensions in millimetres
12311_ed2fig1.EPS
Key
1 measuring device
2 annular clamp
3 direction and point of application of force (maximum 5 N)
4 displacement limiting device (optional)
5 guiding sleeve
6 pressure peg
c boxed centre distance (adjustable)
E1, E2 contact surfaces
a
Adjustable.
Figure 1 — Illustration of frame deformation and filter retention test
6.1.3 Procedure
6.1.3.1 Mount the test sample on the device with the sides of the sample extended and with the front of
the sample facing downwards. Clamp the sample within 2 mm of the boxed centre of one filter (see
Figure 1).
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© ISO 2023 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO/FDIS 12311:2023(E)
If the side
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 12311
ISO/TC 94/SC 6
Personal protective equipment — Test
Secretariat: BSI
methods for sunglasses and related
Voting begins on:
2023-09-14 eyewear
Voting terminates on:
Équipement de protection individuelle — Méthodes d'essai pour
2023-11-09
lunettes de soleil et articles de lunetterie associés
ISO/CEN PARALLEL PROCESSING
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 12311:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 1 ----------------------
ISO/FDIS 12311:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 12311
ISO/TC 94/SC 6
Personal protective equipment — Test
Secretariat: BSI
methods for sunglasses and related
Voting begins on:
eyewear
Voting terminates on:
Équipement de protection individuelle — Méthodes d'essai pour
lunettes de soleil et articles de lunetterie associés
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
ISO/CEN PARALLEL PROCESSING
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.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO
ISO/FDIS 12311:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
© ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 2 ----------------------
ISO/FDIS 12311:2023(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Prerequisites . 1
5 General test requirements . 2
6 Test methods for mechanical properties . 2
6.1 Test method for frame deformation and filter retention . 2
6.1.1 Principle . 2
6.1.2 Apparatus . 2
6.1.3 Procedure . 3
6.1.4 Report. 4
6.1.5 Uncertainty of measurement . 4
6.2 Test method for increased endurance of sunglasses . 5
6.2.1 Principle . 5
6.2.2 Apparatus . 5
6.2.3 Procedure . 5
6.2.4 Report. 10
6.2.5 Uncertainty of measurement . 10
6.3 Test for resistance to perspiration of the sunglass frame . 10
6.3.1 Principle . 10
6.3.2 Apparatus and reagents . 10
6.3.3 Procedure . 11
6.3.4 Report.12
Annex A (normative) Application of uncertainty of measurement .13
Bibliography .15
iii
© ISO 2023 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/FDIS 12311:2023(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 the right to be represented on that committee. International
organizations, governmental and nongovernmental, 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 document 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 94 Personal safety — Personal protective
equipment, Subcommittee SC 6 Eye and face protection, in collaboration with the European Committee
for Standardization (CEN) Technical Committee CEN/TC 85, Eye-protective equipment, in accordance
with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 12311:2013), which has been technically
revised.
The main changes are as follows:
— with the publication of the four parts of ISO 18526 in 2020, which provides test methods and
specifications for head forms for the compliance testing of eye protectors, it was deemed unnecessary
to reproduce details of these test methods in ISO 12311. They have therefore been removed. Test
methods that have been retained in this document are those developed originally for testing of
spectacle frames. Corresponding Annexes that supplemented the now deleted test methods have
also been removed.
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 2023 – All rights reserved
---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 12311:2023(E)
Personal protective equipment — Test methods for
sunglasses and related eyewear
1 Scope
This document specifies reference's test methods for determining the properties of sunglasses given in
ISO 12312 (all parts). It is applicable to all sunglasses and related eyewear.
Other test methods can be used if proven to be equivalent.
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 1042, Laboratory glassware — One-mark volumetric flasks
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4007, Personal protective equipment — Eye and face protection — Vocabulary
ISO 8624, Ophthalmic optics — Spectacle frames — Measuring system and vocabulary
ISO/IEC Guide 983, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4007 and ISO 8624 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/
4 Prerequisites
The following parameters shall be specified prior to testing [see ISO 12312 (all parts)]:
— the number of test samples;
— test sample preparation;
— any conditioning prior to testing;
— characteristics to be assessed subjectively (if appropriate);
— pass/fail criteria.
1
© ISO 2023 – All rights reserved
---------------------- Page: 5 ----------------------
ISO/FDIS 12311:2023(E)
5 General test requirements
Unless otherwise specified, the values stated in this document are expressed as nominal values. Except
for temperature limits, values which are not stated as maxima or minima shall be subject to a tolerance
of ±5 %. Unless otherwise specified, the ambient temperature for testing shall be between 16 °C and
32 °C. Where other temperature limits are specified, they shall be subject to an accuracy of ±2 °C.
Relative humidity shall be maintained at (50 ± 20) %.
Unless otherwise specified, the filters shall be tested at the reference points as defined in ISO 4007.
6 Test methods for mechanical properties
6.1 Test method for frame deformation and filter retention
6.1.1 Principle
This procedure tests the ability of the complete sunglass to resist deformation and to retain the filters.
6.1.2 Apparatus
6.1.2.1 Overall scheme, the test apparatus consists of an annular clamp, a downwardoperating
pressure peg and a measuring device. See Figure 1.
6.1.2.2 Annular clamp, (see Figure 1, key item 2) shall be capable of holding the test sample without
twist or slip and have a diameter of (25 ± 2) mm, with two contact surfaces, E and E , made of a firm
1 2
elastic material (e.g. polyamide). The clamping surfaces shall be capable of being separated at least
10 mm on either side of a horizontal line going through the apparatus. To accommodate frames with a
significant face form angle, the annular clamp shall also be capable of rotating about a horizontal axis
so that the axis of the pressure peg (6.1.2.3) remains vertical and perpendicular to the plane of the
unclamped lens at its boxed centre.
6.1.2.3 Pressure peg, (see Figure 1, key item 5) which operates vertically downwards shall have a
diameter of (10 ± 1) mm with a nominally hemispherical contact surface. The pressure peg shall be
capable of travelling from at least 10 mm above the horizontal line to not more than 8 mm below. The
horizontal distance between the annular clamp and pressure peg is adjustable. The pressure peg slides
in a guiding sleeve (See Figure 1, key item 4) that maintains its vertical orientation and lateral position.
6.1.2.4 Measuring device, to measure the linear displacement of the pressure peg, with an
uncertainty no greater than ±0,1 mm.
2
© ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 12311:2023(E)
Linear dimensions in millimetres
Key
1 measuring device
2 annular clamp
3 direction and point of application of force (maximum 5 N)
4 displacement limiting device (optional)
5 guiding sleeve
6 pressure peg
c boxed centre distance (adjustable)
E , E contact surfaces
1 2
a
Adjustable.
Figure 1 — Illustration of frame deformation and filter retention test
6.1.3 Procedure
6.1.3.1 Mount the test sample on the device with the sides of the sample extended and with the front
of the sample facing downwards. Clamp the sample within 2 mm of the boxed centre of one filter (see
Figure 1).
If the sides are in the way of mounting the frame, e.g. jointless sides, then it is permissible to remove
them, but if so, the endurance test (6.2) shall be performed first. Since the endurance test may be a
more severe test of the frame's mechanical strength, the preferred option is to subject the sample to the
bridge deformation and lens retention test before the endurance test.
Lower the pressure peg so that it rests on the back surface of the unclamped filter within 2 mm of
its boxed centre, ensuring that there is no movement of the filter. Record the reading on the linear
measuring device as the starting position.
3
© ISO 2023 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/FDIS 12311:2023(E)
Move the pressure peg slowly and smoothly downwards, increasing the force until the first of the
following criteria is reached:
a) a maximum force of 5 N;
b) a displacement of the pressure peg from the starting position equal to (10 ± 1) % of the distance
between boxed centres, c. An optional displacement limiting ring (see Figure 1, key item 4) can be
used to
...
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