ISO 14490-5:2017
(Main)Optics and photonics — Test methods for telescopic systems — Part 5: Test methods for transmittance
Optics and photonics — Test methods for telescopic systems — Part 5: Test methods for transmittance
ISO 14490-5:2017 specifies the test methods for the determination of the transmittance of telescopic systems and observational telescopic instruments.
Optique et photonique — Méthodes d'essai pour systèmes télescopiques — Partie 5: Méthodes d'essai du facteur de transmission
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INTERNATIONAL ISO
STANDARD 14490-5
Second edition
2017-08
Optics and photonics — Test methods
for telescopic systems —
Part 5:
Test methods for transmittance
Optique et photonique — Méthodes d’essai pour systèmes
télescopiques —
Partie 5: Méthodes d’essai du facteur de transmission
Reference number
ISO 14490-5:2017(E)
©
ISO 2017
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ISO 14490-5:2017(E)
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ii © ISO 2017 – All rights reserved
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ISO 14490-5:2017(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Test arrangement . 2
5.1 General . 2
5.2 Source of radiation and condenser . 3
5.3 Monochromator or set of filters . 3
5.4 Collimator . 3
5.5 Aperture stop . 3
5.6 Specimen mounting . 3
5.7 Veiling glare stop . 3
5.8 Integrating sphere . 4
5.9 Radiation detector . 4
6 Procedure. 4
6.1 Preparation of the test assembly . 4
6.2 Determination of the measurement values . 4
6.3 Further test methods . 5
7 Precision of the measurement . 5
8 Presentation of the results . 5
9 Analysis . 5
9.1 Effective transmittance for photopic vision . 5
9.2 Effective transmittance for scotopic vision . 6
10 Test report . 6
Annex A (informative) Calibration procedure for the photoreceiver/measuring instrument .7
Annex B (informative) Trichromatic coefficients and colour contribution index.10
Bibliography .14
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ISO 14490-5:2017(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 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
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.
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expressions related to conformity assessment, as well as information about ISO’s adherence to the
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URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee
SC 4 Telescopic systems.
This second edition cancels and replaces the first edition (ISO 14490-5:2005), which has been
technically revised. It also incorporates the ISO 14490-5:2005/Amd 1:2015.
The main changes are as follows:
— the normative references has been updated;
— In 5.8, the wording has been changed to “maximum diameter of the aperture stop”;
— Formulae (3) and (4) have been corrected.
A list of all parts in the ISO 14490 series can be found on the ISO website.
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INTERNATIONAL STANDARD ISO 14490-5:2017(E)
Optics and photonics — Test methods for telescopic
systems —
Part 5:
Test methods for transmittance
1 Scope
This document specifies the test methods for the determination of the transmittance 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 11664-2, Colorimetry — Part 2: CIE standard illuminants
ISO 14132-1, Optics and photonics — Vocabulary for telescopic systems — Part 1: General terms and
alphabetical indexes of terms in ISO 14132
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 Principle
To determine the spectral transmittance τλ , the flux of radiation in a limited bundle of rays will be
()
measured before entering Φ λ and after passing Φ λ through the optical system. The
() ()
0 p
transmittance results from Formula (1):
Φ λ
()
p
τλ = (1)
()
Φ λ
()
0
During the spectral measurement, the emergent light of the radiation source will be limited to a small
wavelength band by means of a monochromator or a set of filters.
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ISO 14490-5:2017(E)
5 Test arrangement
5.1 General
The measuring device consists of radiation source (optionally with a condenser), monochromator or
set of filters, collimator lens, aperture stop, specimen mounting, veiling glare stop, integrating sphere,
radiation detector and measuring and evaluation unit (signal processing).
See Figure 1.
Key
1 radiation source 6 aperture stop
2 condenser 7 integrating sphere
3 monochromator 8 detector
4 selectable diaphragm as field stop 9 baffle
5 collimator lens 10 measurement and evaluation unit
Figure 1 — Test arrangement without test specimen (schematic)
Key
1 radiation source 7 test specimen
2 condenser 8 veiling glare stop
3 monochromator 9 integrating sphere
4 selectable diaphragm as field stop 10 detector
5 collimator lens 11 baffle
6 aperture stop 12 measurement and evaluation unit
Figure 2 — Test arrangement with test specimen (schematic)
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ISO 14490-5:2017(E)
5.2 Source of radiation and condenser
The radiation source shall emit a continuous flux of radiation in the specified wavelength range. The
variation of flux during the measurement of a pair of values shall be less than 1 %. The condenser
adapts the radiation source to the optical measurement path.
5.3 Monochromator or set of filters
Grating or prism monochromators can be used to select the wavelength. The smallest adjustable
wavelength distance shall be less than 2 % of the dominant wavelength of the respective measurement.
The necessary spectral bandwidth depends on the sample. It shall be ensured that a steep alteration of
the transmission curve is detected correctly. Thus, the bandwidth shall be smaller than the distance
in the wavelength, at which the transmittance is changed by 4 %. This condition cannot always be
satisfied because of measuring and energy reasons or because the time/cost effort is not adequate. In
these cases, a maximum bandwidth of 4 % of the wavelength is allowable. A bandwidth of less than 2 %
of the wavelength is necessary if the colour rendition indices are to be calculated.
Instead of a monochromator, a set of filters can be used. They are especially useful with flat-shaped
transmittance curves. The number of measuring points shall allow for a definite curve fitting.
Measurement with spectral filters can be applied as well if only single measuring points are required.
5.4 Collimator
The collimator may contain a refracting lens or mirror. The collimator has to be adjusted to the aligned
components in such a way that full and uniform illumination of the following aperture stop is assured.
The axial chromatic aberration of a refracting lens shall be less than or equal to 1 % of its focal length
in the spectral range used. An off-axis parabolic mirror or an equivalent system is also suitable as a
collimator.
5.5 Aperture stop
The aperture stop should be circular and located close to objective lens of the test specimen if possible.
The diameter should be ≤80 % (50 % recommended) of the maximum available aperture of the test
specimen, as well as smaller than the opening of the integrating sphere. Auxiliary systems can be
used for beam forming to realize these requirements. These systems shall stay in the ray path during
measuring with and without test specimen.
Generally, the smallest possible aperture stop should be used which is compatible with the signal-to-
noise requirements of the detector.
Special care should be taken when measuring telescopic systems with variable magnification where
at some magnification settings the entrance pupil can be considerably smaller than the free objective
lens diameter. In this case, it is recommended to take the entrance pupil as the “maximum available
aperture”.
5.6 Specimen mounting
The mounting of the test specimen shall be designed in a way that the test specimen can be adjusted
and held stable.
The test specimen should be oriented in a way such that no obstructions occur in the measurement
beam (e.g. by reticle structures).
5.7 Veiling glare stop
A veiling glare stop with a diameter that is 1,1 times the diameter of the image of the aperture stop
is located in the image plane of the aperture stop, consequently in the exit pupil of the telescope. The
veiling glare stop shall be dull black on both sides. It shall be designed in a way that the veiling glare
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ISO 14490-5:2017(E)
resulting from the test specimen and upsetting of the measurement result is reduced as far as possible.
It shall further be designed in a way that the necessary radiation for the measurement passes through
unobstructed.
5.8 Integrating sphere
The integrating sphere shall be located near the veiling glare stop to ensure that the light passing
through the veiling glare stop will be completely collected by the integrating sphere. The integrating
sphere has two openings, one for the input of the bundle of rays to be measured and one for the detector.
Both openings shall not be located opposite each other. Direct radiation incident on the detector is
prevented by baffles. The surfaces of the two openings together shall not occupy more than 5 % of
the internal surface of the sphere. The diameter of the integrating sphere opening shall exceed the
maximum diameter of the aperture stop (6 in Figure 1) by 5 % to 7 %.
The reflectance of the internal coating of the integrating sphere shall be as high as possible and diffuse
across the whole spectra
...
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