ISO 14490-3:2021

INTERNATIONAL ISO
STANDARD 14490-3
Third edition
2021-03
Optics and photonics — Test methods
for telescopic systems —
Part 3:
Test methods for telescopic sights
Optique et photonique — Méthodes d'essai pour systèmes
télescopiques —
Partie 3: Méthodes d'essai pour viseurs de tir
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Method of measurement of axial parallax . 1
4.1 Principle . 1
4.2 Test arrangement . 2
4.2.1 General. 2
4.2.2 Collimator . 2
4.2.3 Telescopic sight . 2
4.2.4 Dioptric tester . 3
4.3 Measurement procedure . 3
4.4 Test report . 3
5 Method of measurement of parallax . 3
5.1 Principle . 3
5.2 Test arrangement . 4
5.2.1 General. 4
5.2.2 Collimator . 4
5.2.3 Telescopic sight . 4
5.2.4 Light stop . 4
5.2.5 Auxiliary telescope . 5
5.3 Measurement procedure . 5
5.4 Test report . 6
6 Method of measurement of eye relief range, eye relief and critical eye relief.6
6.1 Principle . 6
6.2 Test arrangement . 6
6.2.1 General. 6
6.2.2 Collimator . 6
6.2.3 Telescopic sight . 6
6.2.4 Measuring magnifier . 7
6.3 Measurement procedure . 7
6.4 Test report . 8
7 Method of measurement of reticle tracking . 8
7.1 Principle . 8
7.2 Test arrangement . 8
7.2.1 General. 8
7.2.2 Collimator . 8
7.3 Test procedure . 9
7.4 Test report . 9
8 Method of measurement of line of sight shift due to zooming . 9
8.1 Principle . 9
8.2 Test arrangement . 9
8.2.1 General. 9
8.2.2 Test specimen mounting .11
8.2.3 Auxiliary telescope .11
8.3 Test procedure .11
8.3.1 Preparation of the test assembly .11
8.3.2 Determination of the measurement values .11
8.4 Precision of the measurement .12
8.5 Test report .12
9 Method of measurement of line of sight shift due to focusing .12
9.1 Principle .12
9.2 Test arrangement .12
9.2.1 General.12
9.2.2 Collimator .13
9.2.3 Telescopic sight .14
9.2.4 Auxiliary telescope .14
9.3 Test procedure .14
9.3.1 Preparation of the test assembly .14
9.3.2 Determination of the measurement values .14
9.4 Precision of the measurement .14
9.5 Test report .14
10 General test report .15
Bibliography .16
iv © ISO 2021 – All rights reserved

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
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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).
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
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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constitute an endorsement.
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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 4, Telescopic systems.
This third edition cancels and replaces the second edition (ISO 14490-3:2016), which has been
technically revised. The main changes compared to the previous edition are as follows:
— critical eye relief added in the test method according to ISO 14135 series and ISO 14132-3.
A list of all parts in the ISO 14490 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.
INTERNATIONAL STANDARD ISO 14490-3:2021(E)
Optics and photonics — Test methods for telescopic
systems —
Part 3:
Test methods for telescopic sights
1 Scope
This document specifies test equipment and test procedures for determination of the following optical
characteristics of telescopic sights:
— axial parallax;
— parallax;
— eye relief range, eye relief, critical eye relief;
— reticle tracking;
— line of sight shift due to zooming;
— line of sight shift due to focusing.
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 14132-1, Optics and photonics — Vocabulary for telescopic systems — Part 1: General terms and
alphabetical indexes of terms in ISO 14132
ISO 14132-3, Optics and photonics — Vocabulary for telescopic systems — Part 3: Terms for telescopic sights
ISO 14135-1:2021, Optics and photonics — Specifications for telescopic sights — Part 1: General-purpose
instruments
ISO 14135-2:2021, Optics and photonics — Specifications for telescopic sights — Part 2: High-performance
instruments
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14132-1 and ISO 14132-3 apply.
4 Method of measurement of axial parallax
4.1 Principle
This test method describes the measurement of the axial distance between the reticle of a telescopic
sight and an image, formed by the objective lens of this telescopic sight (where the reticle is in the first
image plane) or by the objective lens and erecting system (where the reticle is in the second image
plane). The distance between the reticle of the telescopic sight and image plane of the collimator reticle
−1
along the optical axis, p′ , is expressed in dioptres (m ) and measured with the auxiliary telescope.
ax
4.2 Test arrangement
4.2.1 General
Measurement of the axial parallax shall be carried out with the test arrangement shown in Figure 1.
It shall be possible to adjust the alignment of the collimator and the telescopic sight relative to each
other. This can be achieved by adjusting the collimator and/or the telescopic sight.
Key
1 collimator 6 filter
2 telescopic sight 7 reticle of collimator
3 dioptric tester 8 reticle of telescopic sight
4 observer’s eye 9 image plane of collimator reticle
5 illumination unit 10 reticle of dioptric tester
Figure 1 — Test arrangement for measuring axial parallax
4.2.2 Collimator
The collimator shall have a useful diameter larger than the objective lens diameter of the telescopic
sight under test and a focal length of at least ten times the diameter of the collimator lens.
The reticle of the collimator should have geometric features appropriate to assess the offset, e.g. a
cross-hair. The axial position of this reticle shall be correctly adjusted to form an image at the specified
parallax-free distance of the telescopic sight under test.
The illumination unit shall create a uniform brightness over the aperture of the collimator.
To avoid chromatic aberrations, a green filter (~0,55 µm) shall be used.
4.2.3 Telescopic sight
The telescopic sight and/or the collimator shall be adjusted relative to each other so that both optical
axes are parallel and in such a position that the objective lens of the telescopic sight is completely
illuminated.
The centre of the reticle of the telescopic sight shall be near the optical axis of the sight.
2 © ISO 2021 – All rights reserved

4.2.4 Dioptric tester
The dioptric tester shall have an aperture larger than the exit pupil of the telescopic sight and a
magnifying power sufficient to ensure a precise measurement (i.e. ×3 to ×6).
4.3 Measurement procedure
Set the dioptric tester to zero with its eyepiece adjusted to obtain a sharp image of its own reticle.
The eyepiece of the telescopic sight shall be focused on the reticle of the telescopic sight to obtain a
sharp image while viewing through the dioptric tester.
For telescopic sights with a fixed eyepiece, use the dioptric tester to focus on the reticle of the
telescopic sight.
The dioptre setting of the dioptric tester shall be adjusted to obtain a sharp image of the collimator
reticle.
The axial parallax in the image space, p′ , shall be determined by the difference of the two readings on
ax
the dioptric tester.
−1
The uncertainty of measurement for p′ (expressed in m ) shall not exceed Formula (1):
ax
27,
−1
uncertaintymp′≤ (1)
ax
10 ⋅D′
where
-1
p′ is the axial parallax in the image space in m ;
ax
D' is the exit pupil diameter of the telescopic sight expressed in metres.
For exit pupil diameters larger than 7 mm, the value in the formula shall be D′ = 0,007 m.
The axial parallax in the object space, p , is calculated as given in Formula (2):
ax
p′
ax
p = (2)
ax
Γ
where Γ is the magnifying power of the telescopic sight under test.
NOTE The image quality of the test setup (including the telescopic sight under test) influences the
measurement error.
4.4 Test report
A test report shall be presented and shall include the general information specified in Clause 10 and the
result of the test as specified in 4.3.
5 Method of measurement of parallax
5.1 Principle
This method describes the determination of the angular deviation between the aiming lines for on-axis
and off-axis observation.
NOTE For exit pupil diameters of approximately 2 mm or less, only the test method for axial parallax is
appropriate.
5.2 Test arrangement
5.2.1 General
Measurement of the parallax shall be carried out with the test arrangement shown in Figure 2.
It shall be possible to adjust the alignment of the collimator and the telescopic sight relative to each
other. This can be achieved by adjusting the collimator and/or the telescopic sight.
Key
1 collimator 6 filter
2 telescopic sight 7 reticle of collimator
3 auxiliary telescope 8 light stop, off-axis
4 observer’s eye 9 reticle of telescopic sight
5 illumination unit 10 reticle of auxiliary telescope
Figure 2 — Test arrangement for measuring parallax
5.2.2 Collimator
The collimator shall have a diameter larger than the objective lens diameter of the telescopic sight
under test and a focal length of at least ten times the diameter of the collimator lens.
The reticle of the collimator should have geometric features appropriate to assess the offset, e.g. a
cross-hair. The axial position of this reticle shall be correctly adjusted to form an image at the specified
parallax-free distance of the telescopic sight under test.
The illumination unit shall create a uniform brightness over the aperture of the collimator. To avoid
chromatic aberrations, a green filter (~0,55 µm) shall be used.
5.2.3 Telescopic sigh
...