ISO 8600-5:2020
(Main)Optics and photonics — Medical endoscopes and endotherapy devices — Part 5: Determination of optical resolution of rigid endoscopes with optics
Optics and photonics — Medical endoscopes and endotherapy devices — Part 5: Determination of optical resolution of rigid endoscopes with optics
This document applies to rigid endoscopes designed for use in the practice of medicine. Endoscopes having a fibre-optic or opto-electronic imaging system are excluded. It specifies a test method for determining the optical resolution of endoscopes. This document provides a measurement method for characterizing three aspects of the optical resolution of a rigid endoscope. Characteristic A is used to provide a simple measurement of the limiting resolution of the endoscope image. Characteristic B provides a measurement of low spatial frequency resolution and characterizes the sharpness, or contrast, of the endoscope image. Characteristic C provides a measurement of the spatial frequency response of the endoscope image.
Optique et photonique — Endoscopes médicaux et dispositifs d'endothérapie — Partie 5: Détermination de la résolution optique des endoscopes optiques rigides
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INTERNATIONAL ISO
STANDARD 8600-5
Second edition
2020-10
Optics and photonics — Medical
endoscopes and endotherapy
devices —
Part 5:
Determination of optical resolution of
rigid endoscopes with optics
Optique et photonique — Endoscopes médicaux et dispositifs
d'endothérapie —
Partie 5: Détermination de la résolution optique des endoscopes
optiques rigides
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test method . 4
4.1 General . 4
4.2 Apparatus . 5
5 Test report . 6
Annex A (informative) Measurement procedure for Characteristic A, limiting resolution .7
Annex B (informative) Measurement procedure for Characteristic B, Contrast Transfer Function .8
Annex C (informative) Measurement procedure for Characteristic C, Modulation Transfer
Function . 9
Annex D (normative) Contrast transfer function (CTF) and modulation transfer function (MTF) .10
Annex E (informative) Conversion of spatial frequencies .15
Annex F (informative) Example of relay optics .17
Annex G (informative) Measurement frequency .18
Bibliography .19
Foreword
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electrotechnical standardization.
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different types of ISO documents should be noted. This document was drafted in accordance with the
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 172 Optics and photonics, Subcommittee
SC 5, Microscopes and endoscopes.
This second edition cancels and replaces the first edition (ISO 8600-5:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— document has been restructured;
— Clause 2 added;
— Clause 3 revised and updated;
— quality characteristics “Contrast Transfer Function” and “Modulation Transfer Function” as
measurement methods are introduced;
— Measurement with limiting resolution moved to informative Annex A;
— informative Annex B added;
— informative Annex C added;
— normative Annex D added;
— informative Annex E added;
— informative Annex F added;
— informative Annex G added.
A list of all parts in the ISO 8600 series can be found on the ISO website.
iv © ISO 2020 – All rights reserved
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
INTERNATIONAL STANDARD ISO 8600-5:2020(E)
Optics and photonics — Medical endoscopes and
endotherapy devices —
Part 5:
Determination of optical resolution of rigid endoscopes
with optics
1 Scope
This document applies to rigid endoscopes designed for use in the practice of medicine. Endoscopes
having a fibre-optic or opto-electronic imaging system are excluded. It specifies a test method for
determining the optical resolution of endoscopes.
This document provides a measurement method for characterizing three aspects of the optical
resolution of a rigid endoscope. Characteristic A is used to provide a simple measurement of the limiting
resolution of the endoscope image. Characteristic B provides a measurement of low spatial frequency
resolution and characterizes the sharpness, or contrast, of the endoscope image. Characteristic C
provides a measurement of the spatial frequency response of the endoscope image.
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 9334, Optics and photonics — Optical transfer function — Definitions and mathematical relationships
ISO 12233:2017, Photography — Electronic still picture imaging — Resolution and spatial frequency
responses
ISO 15529:2010, Optics and photonics — Optical transfer function — Principles of measurement of
modulation transfer function (MTF) of sampled imaging systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
angular limiting resolution
smallest angle whose vertex is at the entrance pupil (can be approximated by the distal window surface
if the target distance from the distal window is significantly larger than the distance between the distal
window surface and the entrance pupil) of the endoscope at which a line pair (lp) at a given working
distance d can just be resolved with normal visual acuity, with the unit of degrees/lp
Note 1 to entry: Angular limiting resolution is calculated using the formula
α =arctan
dr⋅ d
()
where r(d) is the limiting resolution.
3.2
camera
image detector used in the measurement, which is connected to the endoscope under test via
coupling optics
Note 1 to entry: As used in this standard, the camera includes an image detector (typically CCD or CMOS image
sensor), supporting electronics, and firmware/software used to obtain a digital sampling of the image formed by
the coupling optics.
3.3
contrast
ratio of the difference between the intensities of the brightest and the darkest regions of a bar test
target with square-wave modulation or its image divided by the sum of the intensities of the brightest
and the darkest regions of the target or its image, and subsequently multiplied by 100 to measure as a
percentage
Note 1 to entry: Contrast is given by
II−
maxmin
C()% = ×100
II+
maxmin
where I and I are the intensities of the brightest and darkest regions of the target or its image, respectively.
max min
3.4
contrast transfer function
CTF
plot of contrast (3.3) transfer factor, C , as a function of spatial frequency (3.13), u
TF
Note 1 to entry: Contrast transfer factor is given by
Cu()
out
Cu()=
TF
Cu()
in
where Cu is the output contrast (i.e. the image contrast) and Cu is the input contrast (i.e. the target
() ()
out in
contrast).
Note 2 to entry: If the target has high contrast so that Cu is close to one, Cu can be approximated by
() ()
TF
in
Cu . If C is normalized to 1 at zero frequency, constant Cu will get factored out in the normalization.
() ()
TF
out in
The CTF of an endoscope can be obtained by measuring a series of square-wave bar targets with different
spatial frequencies. The low-frequency contrast of the target as imaged through the endoscope may be measured
with target patches of light and dark large enough that the intensity profile through the patch clearly reaches a
steady value.
Note 3 to entry: For the purposes of the test specified in Characteristic B of this document, the “targets” will be
the bar test targets specified in 4.2.5.2 and the measured results will be the CTF.
3.5
limiting resolution
r(d)
maximum number of line pairs per mm (lp/mm) which can be resolved at a given working distance d of
the endoscope
Note 1 to entry: The limiting resolution is only applicable to Characteristic A.
2 © ISO 2020 – All rights reserved
3.6
maximum image height
radius of a circle which circumscribes the image
Note 1 to entry: If the image is rectangular, the maximum image height is half of the diagonal.
Note 2 to entry: If the image is circular, the maximum image height is the radius of the image circle.
3.7
maximum object height
radius of a circle which circumscribes the portion of the object which can be imaged by the endoscope
Note 1 to entry: If the image is rectangular, the maximum object height is half of the distance between the object
points which map to the corners of the image rectangle.
Note 2 to entry: If the image is circular, the maximum object height is the radius of the object space circle which
maps to the image circle.
3.8
modulation
M
ratio of the difference between the intensities of the brightest and the darkest regions of a sinusoidal
test target or its image divided by the sum of the intensities of the brightest and the darkest regions of
the target or its image, and subsequently multiplied by 100 to measure as a percentage
Note 1 to entry: Modulation is given by
II−
maxmin
M % = ×100
()
II+
maxmin
where I and I are the intensities of the brightest and darkest regions of the image, respectively.
max min
3.9
modulation transfer function
MTF
plot of the modulation (3.8) transfer factor, M , as a function of spatial frequency (3.13) u, for a sine-
TF
wave target
Note 1 to entry: M is a measure of the transfer of modulation from the object to the image.
TF
Note 2 to entry: Modulation transfer factor is given by
Mu()
out
Mu()=
TF
Mu
()
in
where Mu() is the output modulation (i.e. the image modulation) and Mu() is the input modulation (i.e.
out in
the target modulation).
Note 3 to entry: If the target has high contrast so that Mu() is close to one, Mu() can be approximated by
in TF
Mu() . On the other hand, M curves are always normalized to 1 at zero frequency, which make a constant
TF
out
Mu() negligible. The MTF of an endoscope can be obtained by measuring a series of sinusoidal targets with
in
different spatial frequencies, or by other methods such as a slanted-edge target as discussed in 4.2.5.3.
3.10
off-axis limiting resolution
limiting resolution (3.5) at an image point at 70 % of the maximum image height (3.6)
Note 1 to entry: See Figure A.1.
...
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