Optics and photonics -- Test methods for telescopic systems

This document specifies the test methods for the determination of the transmittance of telescopic systems and telescopic observational instruments.

Optique et photonique -- Méthodes d'essai pour systèmes télescopiques

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Published
Publication Date
10-Jun-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
15-May-2021
Completion Date
14-May-2021
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INTERNATIONAL ISO
STANDARD 14490-5
Third edition
2021-06
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 14490-5:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 14490-5:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 14490-5:2021(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 Radiation source and condenser ............................................................................................................................................. 3

5.3 Monochromator or set of filters ............................................................................................................................................... 3

5.4 Collimator .................................................................................................................................................................................................... 3

5.5 Aperture stop ........................................................................................................................................................................................... 3

5.6 Specimen mounting ............................................................................................................................................................................ 4

5.7 Integrating sphere ................................................................................................................................................................................ 4

5.8 Radiation detector ............................................................................................................................................................................... 4

5.9 Selectable diaphragm as field stop ........................................................................................................................................ 4

6 Procedure..................................................................................................................................................................................................................... 4

6.1 Preparation of the test arrangement ................................................................................................................................... 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 radiation detector/measuring instrument .....8

Annex B (informative) Trichromatic coefficients and colour contribution index..............................................11

Bibliography .............................................................................................................................................................................................................................16

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 14490-5:2021(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.

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 172, Optics and photonics, Subcommittee

SC 4, Telescopic systems.

This third edition cancels and replaces the second edition (ISO 14490-5:2017), which has been

technically revised.
The main changes compared to the previous edition are as follows:

— updates in Clause 5, in particular 5.7. "Veiling glare stop" was deleted, clarification of requirements

on "Integration sphere", addition of 5.9;

— updates in Clause 9, in particular 9.1 and 9.2. The function V(λ) for the 2° observer was replaced by

the function V10(λ) for the 10° observer to be consistent with 9.2, where the function V'(λ) for the

10° observer [now called V’10(λ)] was already used;
— clarification of requirements in Clause 10;
— addition of B.4;
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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 14490-5:2021(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 telescopic observational 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/CIE 11664-1:2019, Colorimetry — Part 1: CIE standard colorimetric observers
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
CIE 18.2:1983, Basis of Physical Photometry
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:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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.

0 p
The spectral transmittance is given by Formula (1):
Φ ()λ
τλ = (1)
Φ ()λ

During the spectral measurement, the emergent light of the radiation source will be limited to a narrow

wavelength band by means of a monochromator or a set of filters.
© ISO 2021 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO 14490-5:2021(E)
5 Test arrangement
5.1 General

The test arrangement as given in Figure 1 and Figure 2 consists of a radiation source (optionally with

a condenser, a monochromator or a set of filters, a selectable diaphragm as field stop, a collimator lens,

an aperture stop, a test specimen mounting, an integrating sphere, a radiation detector and a signal

processing unit comprising a radiation detector and a measurement and evaluation unit).

Key
1 radiation source 6 aperture stop
2 condenser 8 integrating sphere
3 monochromator/set of filters 9 radiation detector
4 selectable diaphragm as field stop 10 baffle
5 collimator lens 11 measurement and evaluation unit
Figure 1 — Test arrangement without test specimen (schematic)
Key
1 radiation source 7 test specimen
2 condenser 8 integrating sphere
3 monochromator/set of filters 9 radiation detector
4 selectable diaphragm as field stop 10 baffle
5 collimator lens 11 measurement and evaluation unit
6 aperture stop
Figure 2 — Test arrangement with test specimen (schematic)
2 © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 14490-5:2021(E)
5.2 Radiation source 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. It should be, for example, an achromatic

doublet or an off-axis paraboloidal mirror to avoid introducing too much lateral chromatism into the

optical ray path.
5.3 Monochromator or set of filters

The monochromator or the set of filters can be omitted if the signal processing unit comprises a spectral

detector.

Grating or prism monochromators can be used to select the wavelength. The smallest adjustable

wavelength interval shall be less than 2 % of the dominant wavelength (usually 0,55 µm) of the

respective measurement.

The necessary spectral bandwidth depends on the sample. It should be ensured that a steep change

in the transmission curve is detected correctly. Thus, the bandwidth should be selected such that the

transmittance across the band changes by less than 4 %. This condition cannot always be satisfied

because of technical measurement and energetical 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 contribution indices are to be calculated.

Instead of a monochromator, a set of narrow-band filters (full width half maximum <20 nm) may be

used. They are especially useful with flat-shaped transmission curves. The number of measuring points

shall allow for a definite curve fitting. A measurement with spectral filters instead of a monochromator

is also appropriate if only single measurements are required.
5.4 Collimator

The collimator may contain a refracting lens or a mirror. The collimator shall be adjusted to the aligned

components in such a way that full and uniform illumination of the following aperture stop is assured.

The focal length of the collimator shall be long enough that in relation to the field stop of the collimator

the spot diameter is small enough to pass the image plane of the test specimen and is not obscured by

target marks and internal structures. One-third of the image plane diameter should not be exceeded.

The ray bundle shall be collimated as well as possible within the measurement distance by adjusting

the collimator position. 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 the objective lens of the test specimen if

possible. The diameter should be ≤ 50 % of the entrance pupil 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 the measurement 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.
© ISO 2021 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO 14490-5:2021(E)
5.6 Specimen mounting

The mounting of the test specimen shall be designed in a way that the test specimen can be positioned

and aligned and held stable.

The test specimen should be oriented such that no obstructions occur in the measurement beam (e.g. by

reticle structures).
5.7 Integrating sphere

The distance between the aperture stop and the integration sphere shall be arranged according to the

requirements of the test specimen. The distance shall not be changed during the measurement with

and without test specimen such that the light is always completely collected by the integrating sphere.

To avoid the impact of multiple reflections, a large distance, e.g. 100 mm, between the eyepiece and the

integrating sphere is recommended. The position of the integrating sphere should be chosen so that the

diameter of the ray bundle entering the integrating sphere is almost the same as without the specimen.

The integrating sphere has two openings, one for the input of the bundle of rays to be measured and one

for the detector. The 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 (item 6 in Figure 1 and Figure 2) by at least 5 % to 7 %.

The reflectance of the internal coating of the integrating sphere shall be as high as possible and diffuse

across the whole spectral range. The reflectance across the whole spectral range from 380 nm to

780 nm shall be at least 85 %.
5.8 Radiation detector

The linearity of the signal processing unit (radiation detector together with measurement and

evaluation unit) shall be better than 0,5 %.
5.9 Selectable diaphragm as field stop

The diameter should be selected such that the angular extension on the eyepiece side of the test

specimen does not exceed 5 degrees to avoid pupil and reticle vignetting.
6 Procedure
6.1 Preparation of the test arrangement

Insert the test specimen in its mounting with the objective lens facing the radiation source (see

Figure 1). The entrance and the exit surface of the front lenses of the test specimen shall be clean and

without dust.

Take care to avoid multiple reflections between the aperture stop, the test specimen and other parts,

which may upset the measurement result, by the use of additional protective screens.

For systems with a reticle at an intermediate image plane, take care that parts of the test specimen's

reticle do not obscure any light passing through it. Ensure that the ambient light does not influence the

measurement result.
6.2 Determination of the measurement values
Carry out the measureme
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14490-5
ISO/TC 172/SC 4
Optics and photonics — Test methods
Secretariat: DIN
for telescopic systems —
Voting begins on:
2021-03-19
Part 5:
Voting terminates on:
Test methods for transmittance
2021-05-14
Optique et photonique — Méthodes d'essai pour systèmes
télescopiques —
Partie 5: Méthodes d'essai du facteur de transmission
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 14490-5:2021(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 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 14490-5:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 14490-5:2021(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 Radiation source and condenser ............................................................................................................................................. 3

5.3 Monochromator or set of filters ............................................................................................................................................... 3

5.4 Collimator .................................................................................................................................................................................................... 3

5.5 Aperture stop ........................................................................................................................................................................................... 3

5.6 Specimen mounting ............................................................................................................................................................................ 4

5.7 Integrating sphere ................................................................................................................................................................................ 4

5.8 Radiation detector ............................................................................................................................................................................... 4

5.9 Selectable diaphragm as field stop ........................................................................................................................................ 4

6 Procedure..................................................................................................................................................................................................................... 4

6.1 Preparation of the test arrangement ................................................................................................................................... 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 radiation detector/measuring instrument .....8

Annex B (informative) Trichromatic coefficients and colour contribution index..............................................11

Bibliography .............................................................................................................................................................................................................................16

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 14490-5:2021(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.

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 172, Optics and photonics, Subcommittee

SC 4, Telescopic systems.

This third edition cancels and replaces the second edition (ISO 14490-5:2017), which has been

technically revised.
The main changes compared to the previous edition are as follows:

— updates in Clause 5, in particular 5.7. "Veiling glare stop" was deleted, clarification of requirements

on "Integration sphere", addition of 5.9;
— clarification of requirements in Clause 10;
— addition of B.4;
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.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 14490-5:2021(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/CIE 11664-1:2019, Colorimetry — Part 1: CIE standard colorimetric observers
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
CIE 18.2:1983Basis of Physical Photometry (E)
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:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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.

0 p
The spectral transmittance is given by Formula (1):
Φ ()λ
τλ = (1)
Φ ()λ

During the spectral measurement, the emergent light of the radiation source will be limited to a narrow

wavelength band by means of a monochromator or a set of filters.
© ISO 2021 – All rights reserved 1
---------------------- Page: 5 ----------------------
ISO/FDIS 14490-5:2021(E)
5 Test arrangement
5.1 General

The test arrangement as given in Figure 1 consists of a radiation source [optionally with a condenser,

a monochromator or a set of filters, a selectable diaphragm as field stop, a collimator lens, an aperture

stop, a test specimen mounting, an integrating sphere, a radiation detector and a signal processing unit

comprising a radiation detector and a measurement and evaluation unit.

The monochromator or the set of filters can be omitted if the signal processing unit comprises a spectral

detector.
Key
1 radiation source 6 aperture stop
2 condenser 8 integrating sphere
3 monochromator/set of filters 9 radiation detector
4 selectable diaphragm as field stop 10 baffle
5 collimator lens 11 measurement and evaluation unit
Figure 1 — Test arrangement without test specimen (schematic)
Key
1 radiation source 7 test specimen
2 condenser 8 integrating sphere
3 monochromator/set of filters 9 radiation detector
4 selectable diaphragm as field stop 10 baffle
5 collimator lens 11 measurement and evaluation unit
6 aperture stop
Figure 2 — Test arrangement with test specimen (schematic)
2 © ISO 2021 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 14490-5:2021(E)
5.2 Radiation source 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. It should be, for example, an achromatic

doublet or an off-axis paraboloidal mirror to avoid introducing too much lateral chromatism into the

optical ray path.
5.3 Monochromator or set of filters

The monochromator or the set of filters can be omitted if the signal processing unit comprises a spectral

detector.

Grating or prism monochromators can be used to select the wavelength. The smallest adjustable

wavelength interval shall be less than 2 % of the dominant wavelength (usually 0,55 µm) of the

respective measurement.

The necessary spectral bandwidth depends on the sample. It should be ensured that a steep alteration

of the transmission curve is detected correctly. Thus, the bandwidth should be selected such that the

transmittance across the band changes by less than 4 %This condition cannot always be satisfied

because of technical measurement and energetical 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 contribution indices are to be calculated.

Instead of a monochromator, a set of narrow-band filters (full width half maximum <20 nm) can be

used. They are especially useful with flat-shaped transmission curves. The number of measuring points

shall allow for a definite curve fitting. A measurement with spectral filters instead of a monochromator

is also appropriate if only single measurements are required.
5.4 Collimator

The collimator may contain a refracting lens or a mirror. The collimator shall be adjusted to the aligned

components in such a way that full and uniform illumination of the following aperture stop is assured.

The focal length of the collimator shall be long enough that in relation to the field stop of the collimator

the spot diameter is small enough to pass the image plane of the test specimen and is not obscured by

target marks and internal structures. One-third of the image plane diameter should not be exceeded.

The ray bundle shall be collimated as well as possible within the measurement distance by adjusting

the collimator position. 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 the objective lens of the test specimen if

possible. The diameter should be ≤ 50 % of the entrance pupil 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 the measurement 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.
© ISO 2021 – All rights reserved 3
---------------------- Page: 7 ----------------------
ISO/FDIS 14490-5:2021(E)
5.6 Specimen mounting

The mounting of the test specimen shall be designed in a way that the test specimen can be positioned

and aligned and held stable.

The test specimen should be oriented such that no obstructions occur in the measurement beam (e.g. by

reticle structures).
5.7 Integrating sphere

The distance between aperture stop and integration sphere shall be arranged according to the

requirements of the test specimen. The distance shall not be changed during the measurement with

and without test specimen such that the light is always completely collected by the integrating sphere.

It is recommended to choose a large distance of e.g. 100 mm between eyepiece and integrating sphere

to avoid the impact of multiple reflections. The position of the integrating sphere should be chosen so

that the diameter of the ray bundle entering the integrating sphere is almost the same as without the

specimen.

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 (item 6 in Figure 1) by at least 5 % to 7 %

The reflectance of the internal coating of the integrating sphere shall be as high as possible and diffuse

across the whole spectral range. The reflectance across the whole spectral range from 380 nm to

780 nm shall be at least 85 %.
5.8 Radiation detector

The linearity of the signal processing unit (radiation detector together with measurement and

evaluation unit) shall be better than 0,5 %.
5.9 Selectable diaphragm as field stop

The diameter should be selected such that the angular extension on the eyepiece side of the test

specimen does not exceed 5 degrees to avoid pupil and reticle vignetting.
6 Procedure
6.1 Preparation of the test arrangement

Insert the test specimen in its mounting with the objective lens facing the radiation source (see

Figure 1). The entrance and the exit surface of the front lenses of the test specimen shall be clean and

without dust.

Take care to avoid multiple reflections between aperture stop, test specimen and other parts, which

may upset the measurement result, by the use of additional protective screens.

For systems with a reticle at an intermediate image plane, take care that parts of the test specimen'

...

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