EN ISO 8598-1:2014

SLOVENSKI STANDARD
01-november-2014
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Optics and optical instruments - Focimeters - Part 1: General purpose instruments used
for measuring spectacle lenses (ISO 8598-1:2014)
Optik und optische Instrumente - Scheitelbrechwert-Messgeräte - Teil 1: Instrumente für
den allgemeinen Gebrauch zur Verwendung für die Brillenglas-Messung (ISO 8598-
1:2014)
Optique et instruments d'optique - Frontofocomètres - Partie 1: Instruments pour cas
généraux pour le mesurage des verres de lunettes (ISO 8598-1:2014)
Ta slovenski standard je istoveten z: EN ISO 8598-1:2014
ICS:
11.040.70 Oftalmološka oprema Ophthalmic equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 8598-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2014
ICS 11.040.70 Supersedes EN ISO 8598:1998
English Version
Optics and optical instruments - Focimeters - Part 1: General
purpose instruments used for measuring spectacle lenses (ISO
8598-1:2014)
Optique et instruments d'optique - Frontofocomètres - Optik und optische Instrumente - Scheitelbrechwert-
Partie 1: Instruments pour cas généraux pour le mesurage Messgeräte - Teil 1: Instrumente für den allgemeinen
des verres de lunettes (ISO 8598-1:2014) Gebrauch zur Verwendung für die Brillenglas-Messung
(ISO 8598-1:2014)
This European Standard was approved by CEN on 22 April 2014.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8598-1:2014 E
worldwide for CEN national Members.

Contents Page
Foreword .3
Foreword
This document (EN ISO 8598-1:2014) has been prepared by Technical Committee ISO/TC 172 "Optics and
photonics" in collaboration with Technical Committee CEN/TC 170 “Ophthalmic optics” the secretariat of which
is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by March 2015, and conflicting national standards shall be withdrawn at
the latest by March 2015.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 8598:1998.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 8598-1:2014 has been approved by CEN as EN ISO 8598-1:2014 without any modification.
INTERNATIONAL ISO
STANDARD 8598-1
First edition
2014-09-15
Optics and optical instruments —
Focimeters —
Part 1:
General purpose instruments
Optique et instruments d’optique — Frontofocomètres —
Partie 1: Instruments pour cas généraux
Reference number
ISO 8598-1:2014(E)
©
ISO 2014
ISO 8598-1:2014(E)
© ISO 2014
All rights reserved. Unless otherwise specified, 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
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Technical requirements for general purpose focimeters . 3
5 Metrological requirements . 5
5.1 General . 5
5.2 Reference wavelength . 5
5.3 Performance requirement . 5
6 Test procedures . 8
6.1 General . 8
6.2 Checking the indication errors . 8
6.3 Checking the axis marker for the optical centre of lens . 8
6.4 Checking the alignment of the axis marker . 9
6.5 Checking the adjusting rail . 9
6.6 Checking the non-symmetric error for automated focimeters . 9
6.7 Checking the repeatability of vertex power measurement for automated focimeters .10
6.8 Checking for the centration error .10
6.9 Checking the capability of focimeters to measure tinted lenses .10
6.10 Checking the astigmatic axis repeatability for low-powered cylinder lens .10
6.11 Special procedures for eyepiece focimeters .11
6.12 Criterion for image focusing in manual focusing focimeters .11
7 Marking .11
7.1 Reference to ISO 8598-1 .11
7.2 General information to be supplied by the manufacturer .11
7.3 Additional information to be supplied by the manufacturer .12
Annex A (informative) Use of correction values when measuring spectacle lenses .13
Annex B (informative) Example for evaluation of uncertainty of measurement for automated
focimeters for general use .18
Annex C (normative) Specifications of special reference lenses .24
Annex D (informative) Information for users on the performance of general purpose focimeters
covered by this part of ISO 8598 .26
Bibliography .27
ISO 8598-1:2014(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 172, Optics and photonics, Subcommittee SC 7,
Ophthalmic optics and instruments.
This first edition of ISO 8598-1 cancels and replaces ISO 8598:1996, of which it constitutes a technical
revision. It also incorporates the Technical Corrigendum ISO 8598:1996/Cor.1:1998.
ISO 8598 consists of the following parts, under the general title Optics and optical instruments —
Focimeters:
— Part 1: General purpose instruments
iv © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
Introduction
General purpose focimeters are intended for measurement of contact lenses, single-vision, multifocal
and progressive-power or degressive-power spectacle lenses, both uncut and mounted in spectacle
frames, and for the orientation and marking of spectacle lenses.
INTERNATIONAL STANDARD ISO 8598-1:2014(E)
Optics and optical instruments — Focimeters —
Part 1:
General purpose instruments
1 Scope
This part of ISO 8598 specifies requirements and test methods for general purpose focimeters designed
for the measurement of vertex powers, cylinder axis, prismatic power and prism base setting within a
restricted area at a specified location of a lens. This excludes instruments that can only measure the
whole lens at once.
It is applicable to instruments typically intended for use by the ophthalmic community, with the
capability to demonstrate conformity of lens products with the International Standards existing for
these lenses.
2 Normative references
The following referenced documents are indispensable for the application 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 7944, Optics and optical instruments — Reference wavelengths
ISO 8429, Optics and optical instruments — Ophthalmology — Graduated dial scale
ISO 9342-1, Optics and optical instruments — Test lenses for calibration of focimeters — Part 1: Test lenses
for focimeters used for measuring spectacle lenses
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
adjusting rail
movable rail or bar used as the reference axis for spectacles during measurement and which is aligned
perpendicularly to the optical axis of the focimeter and parallel to the axis direction 0° to 180°
Note 1 to entry: This is also called the lens table or frame rest.
3.2
capability
ability of a system or process to achieve the required performance
3.3
general purpose focimeter
instrument that is used to measure vertex powers, cylinder axis and prismatic effects of spectacle
and contact lenses, to orientate and mark uncut lenses, and to verify the correct mounting of lenses in
spectacle frames
ISO 8598-1:2014(E)
3.3.1
manual focusing focimeter
instrument that allows the operator to view images formed by rays of light passing through a lens and,
by manually focusing and adjusting, to measure the vertex power and identify the principal meridians
Note 1 to entry: For lenses with cylindrical power, the cylinder axis is found using the method provided to locate
the principal meridians of the lens in the area defined by the focimeter aperture. Prismatic power is measured
separately for this type of focimeter.
Note 2 to entry: There are sub-classes of manual focusing focimeter. One type has an eyepiece whereas the other
has a projection screen. With the eyepiece type, the measurement target is focused and viewed through an
eyepiece.
3.3.2
automated focimeter
instrument that measures the vertex power of a lens, in the area defined by the focimeter aperture, in a
single measurement without operator adjustment
3.3.3
continuously indicating focimeter
focimeter with a continuous scale
Note 1 to entry: For the purposes of this part of ISO 8598, this includes both automated instruments when set to
0,06 D or 0,01 D steps and conventional manual focusing instruments.
3.3.4
digitally rounding focimeter
focimeter which displays measured values rounded to the nearest 0,25 D or 0,12(5) D incremental value
3.4
centration error of the instrument
residual prismatic error of the instrument with no lens in place
3.5
indication
〈of a focimeter〉 quantitative value provided as the output of the focimeter
3.6
indication error
difference between the value indicated by the focimeter and the true value of the reference lens
Note 1 to entry: Here the true value of the reference lens, the back vertex power, is calculated using the four
known basic lens parameters: radii of curvature of the front and back surface (r and r ), the centre thickness (t),
1 2
and the refractive index (n) of the reference lens material, using the formulas listed in ISO 9342-1.
Note 2 to entry: When using a measuring instrument, the influence of the uncertainty and indication error of the
device should be considered.
3.7
lens support
mechanical interface of the instrument against which the spectacle lens or the contact lens is placed for
measurement
Note 1 to entry: The focimeter measures the vertex power related to the surface placed against the lens support.
3.8
near portion power
vertex power measured at the near design reference point, as specified by the manufacturer, of a
multifocal, progressive-power or degressive-power lens
2 © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
3.9
non-symmetric error for cylindrical power and cylinder axis
residual error in the indicated cylindrical power and/or the indicated cylinder axis of a spherocylindrical
lens for an automated focimeter after calibration
3.10
non-symmetric prism error of a focimeter
difference in the prismatic power readings when a plano-prism is measured first with its base setting
in one direction and then in the opposite direction, for example, base settings of 180° and 360°, or 90°
and 270°
3.11.1
back vertex power
reciprocal of the paraxial value of the back vertex focal length measured in metres
3.11.2
front vertex power
reciprocal of the paraxial value of the front vertex focal length measured in metres
Note 1 to entry: Conventionally, the back vertex power, in dioptres, is specified as the “power” of a spectacle lens or
a contact lens, although the front vertex power is required for certain purposes, for example in the measurement
of some multifocal lenses or progressive-power lenses.
−1
Note 2 to entry: The unit for expressing vertex power is the reciprocal metre (m ). The name for this unit is the
“dioptre”, for which the symbol is “D”.
4 Technical requirements for general purpose focimeters
4.1 The measuring range shall include vertex powers with a range from at least −20 D to +20 D and
prismatic powers from 0 Δ to at least 5 Δ.
The instrument shall be capable of measuring the axis direction (see ISO 8429) of cylindrical lenses
between 0° and 180°. For prisms, it shall be possible to determine the direction of the base setting
between 0° and 360°.
4.2 For manual focusing focimeters with non-digital display, the dioptric power scale shall have an
interval not greater than 0,25 D and shall be clear enough for interpolations to be made to the nearest
0,12 D or less.
For axis directions (see ISO 8429) the scale interval shall not exceed 5° and shall be clear enough for
interpolations to be made to the nearest degree.
For prismatic power readings, the scale interval shall not exceed 1 Δ and shall be clear enough for
interpolations to be made to the nearest 0,50 Δ.
4.3 For focimeters with digital display in the range from +20 D to −20 D, the minimum step of the
display shall be equal to or lower than 0,06 D. The display shall show at least two decimal digits.
For axis directions, the increment of the digital display shall be 1°.
For prismatic power readings, the minimum step of the digital display shall be equal to or lower than
0,06 Δ.
4.4 The instrument designed to measure spectacle lenses shall be able to measure lenses with a
diameter of at least 80 mm and a thickness of at least 20 mm. Translational movements of the lenses
on the lens support of not less than 30 mm in a direction perpendicular to the optical axis and to the
adjusting rail shall be possible, starting from no more than 10 mm below, in front of, or behind, the optical
axis of the instrument, as applicable. The adjusting rail shall also be capable of movement of not less than
30 mm in a direction perpendicular to its length and the optical axis of the instrument. See Figure 1.
ISO 8598-1:2014(E)
Dimensions in millimetres
Key
1 lens support
2 adjusting rail
Figure 1 — Minimum required movement of the adjusting rail
4.5 The lens support should be designed so that it does not cause any damage to the lens under test
when used in the manner recommended by the manufacturer.
It shall be designed and manufactured so that it will support a lens placed against it, holding the surface
that is in contact with it perpendicular to the optical axis of the focimeter.
The lens support shall not adversely affect the accuracy of measurement by introducing sagittal error.
Examples of suitable lens supports are shown in Figure 2.
a) b)
4 © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
Key
d , d internal diameter of support
1 c
d d external diameter of support
2, e
d = (d + d )/2
3 1 2
h , h height of support
s c
r = (d – d )/4
1 2 1
r = (d – d )/4
2 e c
Figure 2 — Examples of lens supports for spectacle lenses (a) and contact lenses (b)
For spectacle lenses (a), d should be in the range 5 mm to 8 mm while for contact lenses (b), d should be
1 c
4,5 mm ± 0,5 mm. Because of the increased sagittal depth of steeply-curved contact lenses, the contact
lens support is usually smaller in diameter and slightly shorter. The height difference (h – h ) should be
s c
0,55 mm ± 0,02 mm.
NOTE The dimensions of the contact lens support are as specified in ISO 18369-3.
The internal diameter (d , d ) of the lens support for focimeters used for spectacle lens measurement or
1 c
for contact lens measurement shall be stated by the manufacturer.
4.6 The pin mark printed by the axis marker shall be small enough to enable the distance between a
first and a second mark to be distinguished.
NOTE A diameter of 0,7 mm is recommended.
4.7 The instrument shall be designed so that it gives stable measured values in a normal environment
(i.e. a temperature of 23 °C ± 5 °C, and a relative humidity of less than 85 %).
5 Metrological requirements
5.1 General
When tested with the reference lenses specified in ISO 9342-1, both manual focusing and automated
focimeters shall give indication readings for vertex power and prismatic power over their entire claimed
measuring range, and the indication error for the respective true value shall not exceed the limits given
in Tables 1 and 2.
5.2 Reference wavelength
The instrument shall be manufactured to indicate dioptric powers with reference to the green mercury
line λ = 546,07 nm or the yellow helium line λ = 587,56 nm, as given in ISO 7944, and the manufacturer
e d
shall indicate explicitly which wavelength has been selected.
NOTE If the light source used in the focimeter is not centred on the green mercury line λ = 546,07 nm or the
e
yellow helium line λ = 587,56 nm, the user should be able either to set the instrument, or to apply corrections to
d
the indicated values, for lenses made from materials other than the one that was used to calibrate the instrument.
5.3 Performance requirement
5.3.1 Indication error
When tested in accordance with 6.2.1, the instrument, when fitted with the spectacle lens support, shall
not exceed the permissible indication errors given in Tables 1 and 2 when used with the spectacle form
reference lenses specified in ISO 9342-1.
ISO 8598-1:2014(E)
The maximum permissible indication errors given in Tables 1 and 2 correspond to the use of the reference
lenses specified in ISO 9342-1 with the respective true values.
Table 1 — Maximum permissible indication error on measured vertex power for general
purpose instruments
Values in dioptres (D)
Maximum permissible indication error
Instruments with Digitally rounding instruments
Measuring range of vertex power
continuous scale when set to increments of
a
0,25 0,12(5)
< 0 ≥ −5 > 0 ≤ +5 ±0,06 0,0 0,0
< −5 ≥ −10 > +5 ≤ +10 ±0,09 0,0 ±0,12(5)
< −10 ≥ −15 > +10 ≤ +15 ±0,12 0,0 ±0,12(5)
< −15 ≥ −20 > +15 ≤ +20 ±0,18 ±0,25 ±0,12(5)
< −20 > +20 ±0,25 ±0,25 ±0,25
NOTE 1 Calibrating to tighter tolerances (e.g. 10 % of the product tolerance) will improve instrument equivalence and
reduce possible differences between two instruments.
NOTE 2 The user should be aware that when a focimeter is set to read in steps of 0,01 D, the readings may not be true to this
level of precision.
a
The meaning of 0,12(5) is that the instruments has been set to 1/8th dioptre steps, displayed as 0,12 D.
Table 2 — Maximum permissible indication errors on measured prismatic power for general
purpose instruments
Values in prism dioptres (Δ)
Maximum permissible indication error
Measuring range of prismatic Instruments with Digitally rounding instruments
power continuous scale when set to increments of
a
0,25 0,12(5)
> 0 ≤ 5 0,25 0 0,12(5)
> 5 ≤ 10 0,25 0,25 0,25
> 10 ≤ 15 0,50 0,50 0,50
> 15 ≤ 20 0,75 0,75 0,75
> 20 1,00 1,00 1,00
NOTE Calibrating to tighter tolerances (e. g. to 10 % of the product tolerance) will improve instrument equivalence and
reduce possible differences between two instruments.
a
The meaning of 0,12(5) is that the instruments has been set to 1/8th dioptre steps, displayed as 0,12 D.
For automated focimeters, when any of the spherical reference lenses is measured after correct
centration, it shall indicate less than 0,06 D of astigmatic power.
5.3.2 Axis marker for the optical centre of lens
When tested in accordance with 6.3, the position of the axis marker for the optical centre of the lens
shall not deviate from the optical axis of the focimeter by more than 0,4 mm.
5.3.3 Axis marker alignment
When tested in accordance with 6.4, any misalignment of the orientation of the axis marker shall not
exceed the tolerance of ±1° from the 0° to 180° direction of the dial scale for manual focusing instruments
or at the 0° (or 180°) value of the indicated axis for automated focimeters.
6 © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
5.3.4 Adjusting rail
When tested in accordance with 6.5, any misalignment of the adjusting rail shall not exceed the
tolerance of 1° from the position parallel to the 0° to 180° directions of the dial scale for manual focusing
instruments or the 0° (or 180°) value of the indicated axis for automated focimeters.
5.3.5 Capability of measuring tinted lenses
When tested in accordance with 6.9, focimeters should be capable of measuring tinted lenses with
luminous transmittance τ ≥ 18 %. The indicated value from measuring the reference lens and neutral
V
reference filter as specified in Clause C.4 shall remain within the maximum permissible indication
errors of Table 1. The limited capability of measuring tinted lenses shall be stated if the instrument
cannot meet the requirement of measuring tinted lenses with luminous transmittance τ ≥ 18 %.
V
NOTE In practice it may be difficult to measure lenses whose colour departs significantly from neutral if the
transmittance of the lens at the operating wavelength of the focimeter is less than 18 %.
5.3.6 Non-symmetric errors for automated focimeters
5.3.6.1 General
The cylindrical power, cylinder axis and prism error requirements are for automated focimeters that
measure sphere, cylinder, cylinder axis and prism simultaneously.
5.3.6.2 Non-symmetric error for cylindrical power
When tested in accordance with 6.6.2, the non-symmetric error for the indicated power readings of the
spherocylindrical-power reference lens specified in Clause C.3 shall not exceed 0,06 D sph/0,09 D cyl.
5.3.6.3 Non-symmetric error for cylinder axis
When tested in accordance with 6.6.3, the non-symmetric error for the cylinder axis from each reading
of the spherocylindrical-power reference lens specified in Clause C.3 for each orientation shall not
exceed ±1°.
5.3.6.4 Non-symmetric prism error
When tested in accordance with 6.6.4, the non-symmetric error for prismatic power for an automated
focimeter shall not exceed 0,06 Δ. At the same time, the indicated values for the spherical and cylindrical
powers shall not exceed ± 0,06 D.
5.3.7 Repeatability for the indication reading of automated focimeters
When tested in accordance with 6.7, the repeatability for indication readings for an automated focimeter
shall not exceed 0,06 D within the spherical power range −10 D to +10 D, and shall not exceed 0,12 D
within the measuring range over ±10 D.
5.3.8 Centration error for manual focusing focimeters
When tested in accordance with 6.8, the residual prismatic error of the focimeter with no lens in place
shall not exceed 0,1 Δ.
5.3.9 Astigmatic axis repeatability for low-powered cylindrical lenses with manual focimeters
When tested in accordance with 6.10, the standard deviation of the axis readings for a 0,25 D cylindrical
lens shall be less than 4°.
ISO 8598-1:2014(E)
6 Test procedures
6.1 General
The reference lenses described in ISO 9342-1 shall be used to verify that the requirements of 5.1 to 5.3
are met.
The initial calibration of the focimeter and the metrological verification shall be carried out using all of
those reference lenses in the reference lens set specified in ISO 9342-1 that are within the measuring
range of the instrument.
Manual focusing focimeters should, before use, be set up according to 6.11 and the target focused
according to 6.12.
6.2 Checking the indication errors
6.2.1 Checking the indication errors for vertex power
The spherical reference lenses shall be used to check whether the vertex powers measured by the
focimeter meet the permissible indication errors shown in Table 1.
Ensure that the lens support used is the correct one for the reference lens set selected according to 6.1.
Place each individual reference lens with its back surface against the lens support, and centre it on the
optical axis of the focimeter.
Measure and record the vertex power.
It is recommended that three independent readings be taken for each reference lens and that the mean
value be calculated and taken as the actual measured value of the lens.
NOTE The term “independent reading” means that the reference lens is removed from the support and
replaced again between each reading.
6.2.2 Checking the indication errors for prismatic power
The prismatic reference lenses shall be used to check whether the prismatic powers measured by the
focimeter meet the permissible indication errors shown in Table 2.
For prismatic power measurement, it is recommended that for each of the reference prisms, an
independent reading be taken corresponding to each of the 180° and 360° base setting directions. Take
the larger reading of the two measured values at 180° and 360° directions as the actual measured value
of the reference lens in order to calculate the indication errors.
6.3 Checking the axis marker for the optical centre of lens
A spherical reference lens of at least +15 D shall be used to check whether the axis marker for the optical
centre of lens meets the requirement in 5.3.3.
Centre the lens so that the indicated prism power is zero, and then mark it with the axis marker. Rotate
the reference lens through approximately 180° and re-centre to zero indicated prism power. Re-mark the
lens. Half the distance between the centres of the central marks from the first and second measurements
is the distance between the position of the axis marker for the optical centre of the lens and the optical
axis of the focimeter.
8 © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
6.4 Checking the alignment of the axis marker
The 5 D plano-cylindrical reference lens as specified by ISO 9342-1 shall be used to check whether the
alignment of the axis marker meets the requirement in 5.3.2. The axis marker shall be checked using the
horizontal centreline on the reference lens.
For manual focusing focimeters, place the 5 D plano-cylindrical reference lens on the lens support with
its reference side roughly parallel to the 0° to 180° direction of the dial scale. Mark the lens after focusing
and positioning the lens so that a sharp image line formed by the cylinder axis of the reference lens is
coincident with the 0° to 180° direction of the dial scale.
For automated focimeters, set the instrument to read in positive transposition, and place the 5 D plano-
cylindrical reference lens on the lens support with its reference side roughly parallel to the 0° to 180°
direction. Mark the lens after correctly positioning the lens so that the indication of the axis value
becomes 0° (or 180°).
The angular deviation between the marked dotted line and the horizontal centreline on the 5 D plano-
cylindrical reference lens is the misalignment of the orientation of the axis marker.
6.5 Checking the adjusting rail
For manual focusing focimeters, place the 5 D plano-cylindrical reference lens on the lens support with
its reference side in contact with the adjusting rail. After focusing to the non-zero principal meridian,
move the plano-cylindrical reference lens together with the adjusting rail so that a sharp horizontal line
of the test target runs through the centre of the dial scale.
The angular deviation of this line from the 0° to 180° direction of the dial scale (which represents the
angular error between the adjusting rail and the dial scale) is the misalignment of the adjusting rail.
For automated focimeters, set the instrument to read in positive transposition and place the 5 D plano-
cylindrical reference lens on the lens support with its reference side in contact with the adjusting rail.
After moving the lens together with the adjusting rail so that the indication of the vertical prism value
becomes 0 Δ, the deviation of the indicated cylinder axis from 0° (or 180°) is the misalignment of the
adjusting rail.
6.6 Checking the non-symmetric error for automated focimeters
6.6.1 General
This procedure shall be used only for automated focimeters.
The spherocylindrical-power reference lens specified in Clause C.3 shall be used to check whether the
non-symmetric error for cylindrical power reading and cylinder axis meet the requirements of 5.3.6
according to following procedure.
6.6.2 Checking the non-symmetric error for cylindrical power
Place the spherocylindrical-power reference lens on the lens support with one of its sides against the
adjusting rail, and then centre it in order to obtain the spherical-cylindrical power and axis readings.
Rotate the lens through 45° so that an adjacent side is on the adjusting rail and measure the spherical-
cylindrical power and new axis direction. Repeat until eight spherocylindrical power and axis readings
are obtained, one for each side of the lens.
The absolute value of the difference between the maximum and minimum readings for the cylindrical
power among the eight cylindrical power measurements is the non-symmetric error for cylindrical
power.
ISO 8598-1:2014(E)
6.6.3 Checking the non-symmetric error for cylinder axis
Using the eight axis values found in 6.6.2, calculate the difference between the value found for each side
and the value found for the side 45° clockwise from it. Each of the eight differences thus found shall not
differ from 45° by more than 1°.
6.6.4 Checking the non-symmetric prism error
Using the prism reference lens of 2 Δ specified in ISO 9342-1, obtain a pair of prism power readings for
base settings of 180° and 360°.
Repeat for base settings of 90° and 270°.
The difference between the two readings of each pair is the non-symmetric prism error.
6.7 Checking the repeatability of vertex power measurement for automated focimeters
Using the negative and positive spherical reference lenses of nominal power 5 D and 15 D, take three
readings for each lens with the instrument set at the 0,06 (or smaller) indication step. Additional
measurements may also be made on reference lenses of other powers. The difference between the
maximum and minimum indication reading of each lens is the repeatability of vertex power measurement.
6.8 Checking for the centration error
This procedure shall be used only for manual focusing focimeters. Use the procedure given in 6.12 with
no lens or prism in place.
The deviation between the centre of the eye-piece or projection screen reticule and the target shall not
be more than 0,1 Δ.
6.9 Checking the capability of focimeters to measure tinted lenses
Use the reference filter specified in Clause C.4.
First, measure a spherical reference lens as specified in ISO 9342-1 and record the vertex power reading
with no filter in place. Keeping the powered reference lens against the lens support, place the filter in the
measurement beam with the spherical reference lens still in place against the lens support and record
the vertex power reading. The measured values should meet the requirements specified in 5.3.5.
During the second measurement, check the following:
a) Is it easy to centre the lens?
b) Is the indication reading provided stable or fluctuating?
c) Are both readings within the maximum permissible indication error specified in Table 1?
6.10 Checking the astigmatic axis repeatability for low-powered cylinder lens
This procedure shall be used only for manual focimeters.
Place a lens of positive or negative cylindrical power 0,00 D/±0,25 D on the spectacle lens support at
any axis. It is recommended that the lens be an ophthalmic trial case lens but a spectacle lens complying
with ISO 8980-1 may also be suitable provided the cylindrical power is 0,25 D ± 0,06 D.
Position the lens so that the image is in the centre of the field of view, and measure and record the
cylinder axis. To obtain subsequent independent readings, defocus the instrument with the power
adjustment control and rotate the eyepiece reticule and, if appropriate, the orientation of the target,
10 © ISO 2014 – All rights reserved

ISO 8598-1:2014(E)
without touching the test lens. Make at least a further nine independent readings and calculate the
standard deviation.
NOTE This test should be performed by an experienced focimeter user who has good visual acuity.
6.11 Special procedures for eyepiece focimeters
6.11.1 Setting-up procedure
Set the instrument to read 0,00 D.
Unscrew the eyepiece out fully. Look through the eyepiece and slowly screw the eyepiece in until the
image of the target just comes into focus.
NOTE If the eyepiece is screwed too far in for any particular operator this will induce ocular accommodation
and increase the measurement error.
6.11.2 Checking for the absence of parallax
After focusing the target as described in 6.11.1, check for the absence of parallax. The observer shall
move his/her eye from side to side above the eyepiece. During this movement, the image of the target
shall not move noticeably with respect to the cross hairs.
6.12 Criterion for image focusing in manual focusing focimeters
Generally, the target designs in a manual focusing focimeter are in one of four forms: a circle of dots,
cross lines, a combination of cross lines and a circle of dots, or a combination of cross lines and a circle
of dots with several rows of dots in the middle. Obtaining indication values of dioptric power requires
focusing of the target by the operator. Due to the different forms of target in manual focusing focimeters,
a common criterion for image focusing is required to avoid the deviation of indication readings caused
by differences in image focusing criteria between operators.
NOTE 1 If the target is in the form of a circle of dots, or cross lines, or a combination of a circle of dots and cross
lines, the best focus plane should be chosen as the best overall focus.
NOTE 2 Contact lenses have very steep curvature giving spherical aberration. This may affect the results when
measuring the power. If the target is in the form of a circle of dots, the best focus plane should be chosen as the
best overall focus. If the target is in the form of cross lines, the best overall focus should be selected for the central
area of apparent diameter about 20 mm.
7 Marking
7.1 Reference to ISO 8598-1
If the manufacturer or supplier claims compliance with this part of ISO 8598, reference shall be made to
ISO 8598-1 either on the package or in available literature.
7.2 General information to be supplied by the manufacturer
The packaging shall be marked, but not be limited to the following information:
a) name and address of the manufacture and/or trade name;
b) serial number;
c) any warning and/or precautions to take.
ISO 8598-1:2014(E)
7.3 Additional information to be supplied by the manufacturer
The information shall include, but not be limited to, the following:
a) the reference wavelength used for calibration;
b) how to change the Abbe number setting, if needed;
c) the measurement range;
1)
d) the optical system principle used, i.e. either Focus on Axis (FOA) or Infinite on Axis (IOA) ;
e) the limited capability of measuring tinted lenses should the instrument not meet th
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