ISO 14490-7:2016

INTERNATIONAL ISO
STANDARD 14490-7
Second edition
2016-11-15
Optics and photonics — Test methods
for telescopic systems —
Part 7:
Test methods for limit of resolution
Optique et photonique — Méthodes d’essai pour systèmes
télescopiques —
Partie 7: Méthodes d’essai pour limite de résolution
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Method of determination of the limit of resolution . 1
4.1 General . 1
4.2 Test equipment . 1
4.3 Preparation and carrying out of measurements . 3
4.4 Determination of results . 3
5 Test report . 4
Annex A (informative) Dimensions of a bar-type test target for determination of the limit
of resolution of telescopic systems . 5
Bibliography .10
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
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on the ISO list of patent declarations received (see www.iso.org/patents).
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Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 172, Optics and photonics, Subcommittee SC 4,
Telescopic systems.
This second edition cancels and replaces the first edition (ISO 14490-7:2005), which has been
technically revised with the following changes:
-1/3
— addition of a new sentence in A.4 “Alternatively, a test pattern down to 2 = 0,79 is acceptable.”;
— corrected Table A.2, last row: 302 replaced by 320.
A list of parts in the ISO 14490 series can be found on the ISO website.
iv © ISO 2016 – All rights reserved

Introduction
There are various characteristics which are relevant for overall image quality of telescopic systems and
observational telescopic instruments. Two important characteristics are the limit of resolution and the
optical transfer function.
This document specifies the test method for the determination of the limit of resolution of telescopic
systems and observational telescopic instruments. Optical transfer function measurement as applied
to telescopic systems is specified in ISO 9336-3.
Besides the limit of resolution and the optical transfer function, further characteristics are relevant for
an assessment of the image quality; the most important of them are the following:
— secondary spectrum (dispersive aberrations);
— distortion;
— vignetting;
— colour matching.
The secondary spectrum of the test specimen can produce colour fringes surrounding observed objects
(especially at high contrast edges) which can look like coloured neon tube light.
The perceived image might have barrel or pincushion distortion. Pincushion distortion is considered to
give a more natural impression of the observed object when swivelling the test specimen.
Vignetting can lead to a perceivable intensity degradation from the centre to the edge of the field of view.
Colour matching is the accuracy of the colour rendition of an object observed with the test specimen.
Any colour deviation might be due to the lens material or to coatings.
INTERNATIONAL STANDARD ISO 14490-7:2016(E)
Optics and photonics — Test methods for telescopic
systems —
Part 7:
Test methods for limit of resolution
1 Scope
This document specifies the test methods for the determination of the limit of resolution of telescopic
systems and observational telescopic instruments.
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 14490-1:2005, Optics and optical instruments — Test methods for telescopic systems — Part 1: Test
methods for basic characteristics
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14132-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
4 Method of determination of the limit of resolution
4.1 General
The limit of resolution of a telescopic system is the minimum angular distance between centrelines of
two adjacent bright (or dark) bars of the bar-type resolution test target whose direction can be detected
when viewing through the test specimen.
4.2 Test equipment
The limit of resolution of telescopic systems shall be determined with the test arrangement shown in
Figure 1.
The bar-type resolution test target has contrast, as given by Formula (1):
ττ−
tr op
K = ≥ 09, (1)
ττ+
tr op
where
τ is the transmittance of a translucent part of the resolution test target;
tr
τ is the transmittance of an opaque part of the resolution test target.
op
The resolution test target shall be placed at the focal plane of the collimator lens.
For systems that require the limit of resolution to be measured with a focus setting other than infinity,
the position of the resolution test target with respect to the collimator lens shall be adjusted in order to
obtain its image at the specified distance from the test specimen.
The bar-type resolution test target is a glass plate bearing a picture that consists of bright bars having
different widths on a dark background, the directions of which are vertical, horizontal and diagonal in
± 45 angular degrees.
The dimensions of one acceptable design of bar-type resolution test target are given in Annex A.
The resolution test target shall be illuminated uniformly (mean illuminance ±5 % Peak to Valley) by
means of a light source with a correlated colour temperature of 5 000 K to 6 000 K, condenser and
diffuser for non-dazzling observation conditions. The luminance of the resolution test target shall be
optimum for observation of its image.
The diameter of the collimator lens shall at least exceed 1,2 times the diameter of the entrance pupil of
the test specimen. The focal length of the collimator lens shall be at least five times that of the objective
of the test specimen.
The magnification of the auxiliary telescope shall not reduce the diameter of the exit pupil of the whole
system below 0,8 mm.
Key
1 light source
2 condenser
3 diffuser
4 bar-type resolution test target
5 collimator lens
6 test specimen
7 auxiliary telescope
The auxiliary telescope should not be used if the angular limit of resolution behind the eyepiece of the test specimen
is worse than 2’ to 3’ and the diameter of the exit pupil is below 1 mm.
Figure 1 — Test arrangement for measurement of the limit of resolution (schematic)
2 © ISO 2016 – All rights reserved

4.3 Preparation and carrying out of measurements
Stray light and vibration sh
...