medical photonics lecture 1.2 optical engineering · 2016. 12. 12. · field of view small, 5°...
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Medical Photonics Lecture 1.2Optical Engineering
Lecture 9: Instruments I
2016-12-15
Michael Kempe
Winter term 2016
2
Contents
No Subject Ref Date Detailed Content
1 Introduction Gross 20.10. Materials, dispersion, ray picture, geometrical approach, paraxial approximation
2 Geometrical optics Gross 03.11. Ray tracing, matrix approach, aberrations, imaging, Lagrange invariant
3 Components Kempe 10.11. Lenses, micro-optics, mirrors, prisms, gratings
4 Optical systems Gross 17.11. Field, aperture, pupil, magnification, infinity cases, lens makers formula, etendue, vignetting
5 Aberrations Gross 24.11. Introduction, primary aberrations, miscellaneous
6 Diffraction Gross 01.12. Basic phenomena, wave optics, interference, diffraction calculation, point spread function, transfer function
7 Image quality Kempe 08.12. Spot, ray aberration curves, PSF and MTF, criteria
8 Instruments I Kempe 15.12. Human eye, loupe, eyepieces, photographic lenses, zoom lenses, telescopes
9 Instruments II Kempe 22.12. Microscopic systems, micro objectives, illumination, scanning microscopes, contrasts
10 Instruments III Kempe 05.01. Medical optical systems, endoscopes, ophthalmic devices, surgical microscopes
11 Optic design Gross 12.01. Aberration correction, system layouts, optimization, realization aspects
12 Photometry Gross 19.01. Notations, fundamental laws, Lambert source, radiative transfer, photometry of optical systems, color theory
13 Illumination systems Gross 26.01. Light sources, basic systems, quality criteria, nonsequential raytrace
14 Metrology Gross 02.02. Measurement of basic parameters, quality measurements
The Human Eye
Ref: Wikipedia
The Eye of Owl, Cat, Gecko, Insects
Ref: Wikipedia
The Human Eye
cornea
pupil
iris
tear liquid
front chamber
conjunctiva
conjunctiva
lens vitreous body
macula(yellow)
retina
blind spot
rear chamber
muscle
muscle
nerve
fibres
fibres
outer skin
choroidmembrane
The Human Field of View
Ref: Wikipedia
< 10°: central< 30°: near-peripheral< 60°: mid-peripheral
The Human Vision
Optical Data of the Eye
Property relaxed accomodatedRefractive power 58.63 dptr 70.57 dptrFocal length in air 17.1 mm 14.2 mmPower of the crystalline lens 19 dptr 33 dptrPupil diameter, smallest value for high brightness 1.5 mmPupil diameter, largest value for night vision 8.0 mmAbbe number (approx.) 50.23Petzval radius -17.58 mmLocation of entrance pupil -3.047 mmField of view maximum (vertical) 108°Field of view maximum (horizontal) 200°Field of foveated seeing 5°Diameter eye ball 24 mmDistance rotation point from cornea vertex 13.5 mmNodal point location 7.33 mmPrincipal plane location 1.6 mm
Eye Data - Overview
Terms Sizes and lengths
retina
fovea
cornea
iris
optical discblind spotcrystalline lens
lens capsule
anteriorchamber
posteriorchamber
vitreoushumor
temporal
nasal
0.5 mm3.6 mm
3.6 mm
F'
F
24.4 mm15.7 mm
NN'PP'
1.6 mm
7.33 mm
C
13.5 mm
1.8 mm
4 mm
1.8 mm
2.5 mm
Refractive Index
Distribution of the indexalong z
Smooth index variationof crystalline lens
z[mm]
n
0 5 10 15 20 251
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
cornea crystallinelens
lenscapsule retina
vitreous humoranterior
chamber
n
z[mm]0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
1.3
1.32
1.34
1.36
1.38
1.4
1.42
Spectral Transmission of the Eye
Absorption of the eye media prevents retina damage Special truncation of UV and IR contributions
3000
20
40
60
80
100
500400 800600 1000 1400 2000λ [nm]
T [%]visible
after corneabefore lensafter lensat retina
Receptors, rods and cones
Cones : Fovea, bright light, color Rods : Peripheral, dim light, no color Blind spot :
no receptors Fovea : 2° field
eccentric
Property cones rods Location in the fovea outside the fovea Field of view small, 5° large, 108° Resolution and visual acuity large small Brightness sensitivity small, for daylight vision large, vision at night Colour sensitivity yes no Total number of elements 5 million 120 million Limiting brightness 683 lm / W 1699 lm / W Spectral maximum 555 nm 507 nm
Range Diameter [mm]
Cones Rods
Foveola 0.35 number :3500
density 190000/mm2 pitch 2.3 µm
no rods
Fovea 1.85 density : 100000/mm2 pitch : 3.2 µm a few rods
Prafovea 2.85
Macula lutea
Perifovea 5.85 density : 160000/mm2 pitch : 2.5 µm
Periphery density : 5000/mm2 pitch : 14.0 µm
density : 50000/mm2 pitch : 4.5 µm
Papille, blind spot 4 mm off axis nasal 1.8 no cones no rods
(primary)
Spectral Sensitivity of the Eye
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
V(λ)
λ
nightscotopic
rods
dayphotopic
cones
cyan green
Log V(λ)
λ
10-1
400 450 500 550 600 650 700 750400 450 500 550 600 650 700 750
10 0
10-2
10-3
10-4
10-5
Spectral sensitivity of the eye:- Depends on brightness
Daylight / high brightness: cones, peak sensitivity at 550 nm
At night/ low Brightness: rods, peak sensitivity at 507 nm, shifted towards blueNo color distinction
Accomodation
Change of accomodation rangedue to aging
age inyears
∆D [dpt]
16
12
8
4
00 20 40 60
maximum
minimum
meandpt
0 20 40 8060
age[years]
relaxedeye
strongestaccomodation
immobilepoint
4
0
-4
-8
-12
Adaptation
Aging effect on adaptation Aging effect on adaptation speed
8
6
4
2
00 20 40 60 age in
years
pupil diameter[mm]
cones
rods
Log Ithresh[a.u.]
2
3
10 20 30 40
4
5
6
7
8
time[min]
80 years
50 years
30 years17 years
7
kink ofHelmholtz
rod mono-chromate
nightblindness
Gullstrand Model Eye
Six media Crystalline lens with shell Data for relaxed and accomodated eye Simple version : single crystalline lens
Relaxed Accomodated Parameter Notation Value Value
Focal length object sided f [mm] 17.055 14.169 Focal length image sided f' [mm] 22.785 18.930 Refractive power F [dpt] 58.636 70.57 Location entrance pupil p [mm] 3.045 2.667 Location exit pupil p' [mm] 3.664 3.211 Principal point object sided P [mm] 1.348 1.772 Principal point image sided P' [mm] 1.602 2.086 Nodal point object sided N [mm] 7.078 6.533 Nodal point image sided N' [mm] 7.332 6.847 Length L [mm] 24.387
30°
10°
0°
0°
486 nm 587 nm 656 nm
10°
20°
Resolution of the Eye
Resolution of the eye dependson the shape
The quantitative measure isgiven as angle
Rough measure :2𝛼𝛼𝑐𝑐 = 0.017° ≈ 1′
Least distance of (comfortable) distictinct vision: 250 mm
∆x'c = 75 µm
so = 250 mm
L = 22 mm
αc
∆x
distancecones
a) letter5'
b) grating2'
c) two points1'
d) nonius10''
e) binocular 5''
Testchart Acuity of the Eye
Regular testchart
18
EF P
T O ZL P E DP E C F DE D F C F D
F E L O P Z DD E F P O T E C
L E F O D P C T
F D P L T C E O
P E Z O L C F T D
Visual Acuity
Recognition of simple geometricalshapes :
1. Landolt ring with gap2. Letter 'E' Blur of image on retina with distance
a)
5a
a
a
3a
3a
a
3a
b)
distance 6.096 m
blockletter
E 8.9mm
imageheight25 µm eye
original blur : a/2 blur : a blur : 2a blur : 3a blur : 4a
3a
Eye Diseases
Four major defects
a) refraction error b) glaucom
c) retina defects d) cataract
original
Spectacles
Correction of refraction error by spectacle lenses
1. Myopia (short-sightedness) : negative lens
2. Hyperopia (far-sightedness) : positive lens
eye binocular
∞
eye binocular
∞
Lens close to the eyeReference distance so = 250 mmrelaxed eye Magnification
Angle magnification
Loupe Magnifier
s = 250 mmo
f lens
y
y'lens
eye
y
lens
eye
object
so
wo wm
fL
'0
fs
mag =∞Γ
''
tantan
fs
syfy
wwm o
o
o
mw ===
General case :Loupe distance d from the eye :Magnification
Loupe Magnifier
yy'
lens
eye
ss' d
objectvirtualimage
+⋅
+= 1
''
' fs
sdsmw
Eyepiece: Basic Setup
Eyepieces images a finite image of an instrument to infinity Viewing with a relaxed eye Magnification
Objective exit pupil = entrance pupil of eyepiece Eyepiece exit pupil = eye pupil (size: 2-8 mm) Eye relief : distance between last lens surface and eye cornea
- required : 15 mm- with eyeglasses : 20 mm
Objectiveexit pupil
intermediatefocus
Eyepiece
Eye pupil
tube length
eyepiecefmm250
=Γ
Pupil mismatch Eye relief, spherical aberration, eye movement
25
Mismatch of Eyepieces
Ref: Smith, Ceragioli, Berry, Telescopes, Eyepieces, Astrographs, Willman-Bell, 2012
Evolution of Eyepiece Designs
Monocentric
Plössl
Erfle
Von-Hofe
Erfle diffractive
Wild
Erfle type(Zeiss)
BerteleScidmore
Loupe
Erfletype
Bertele
Kellner
Ramsden
Huygens
Kerber
König
Nagler 1
Nagler 2
Bertele
Aspheric
Dilworth
Huygens Eyepiece
Distance
Lateral color corrected Intermediate image between
lenses, not corrected Performance
Virtual object(image plane of objective)
Exit pupil(eye position)
d
221 ffd +
=
-1.000 0.000 1.000
0.250
0.500
0.750
1.000
LONGITUDINALSPHERICAl ABER.
DIOPTER-3.000 0.000 3.000
2.125
4.250
6.375
8.500
tan sag
ASTIGMATICFIELD CURVES
DIOPTER-20.00 0.00 20.00
2.125
4.250
6.375
8.500
DISTORTION
Distortion (%)
0°
10°
20°
20 a
rcm
in
Kellner Eyepiece
Corresponds to Ramsden type Intermediate image accessible Field lens moved Eye lens achromatized
-1.000 0.000 1.000
0.250
0.500
0.750
1.000
LONGITUDINALSPHERICAl ABER.
DIOPTER-3.000 0.000 3.000
2.625
5.250
7.875
10.500
tan sag
ASTIGMATICFIELD CURVES
DIOPTER-20.00 0.00 20.00
2.625
5.250
7.875
10.500
DISTORTION
Distortion (%)
0°
10°
20°
24°
20 a
rcm
in
Collimation
D
source
θG/2divergence
f
u
Collimating source radiation:Finite divergence angle is reality Geometrical part due to finite size :
Diffraction part:
Defocussing contribution to divergence
fD
G =θ
WD 2λθ ≈
uf
z sin2⋅−=
∆∆θ
2W
Typical Photographic Lens Types
Type focal
length in mm
Typical f-number
Field of view (full diagonal)
in degrees
Lens type element number
Fisheye 6 - 10 4 - 2.8 220 - 180 Fisheye 7 - 12
quasi-fisheye 10 - 16 3.5 180 - 100 Fisheye 6 - 10
extreme wide-angle 13 - 18 3.5 120 - 100 retrofocus 9 - 13
very large angle 20 - 24 2.8 - 2 94 - 84 retrofocus 8 - 10
wide-angle 28 - 35 2 - 1.4 75 - 62 Double Gauss, retrofocus 6 - 9
standard 40 - 55 1.4 - 1 56 - 43 Triplet, Tessar, Sonnar, Double Gauss 3 - 7
short telephoto 75 - 105 2.8 - 1.4 37 - 23 Double Gauss, telephoto 5
medium telephoto 120 - 200 4 - 2 21 - 12 Tessar, telephoto 4 - 6
long telephoto 300 - 500 8 - 2.8 8 - 5 telephoto 4 - 7
extreme telephoto 600 - 1200 11 - 5.6 4 - 2 telephoto 2 - 5
Requirements of Photo Objective Lenses
Large field of view- correction of coma, astigmatism, distortion an field curvature
Color correction Resolution
- small F-number- usually the sensor is limiting, not diffraction limited correction
Smart system, small and light weight- short length- plastic components
Additional functionalities- zoom option- focussing- autofocus function- large field viewer
Tessar
Double Gauss
Super Angulon
Photographic Lenses
Distagon
Tele system
Wide angleFish-eye
Example lensfisheye
Fish-Eye-Lens
0°
50°
100°
71°
486 nm 587 nm 656 nma)
ν[mm-1]
tansag
0 20 40 60 80 1000
0.2
0.4
0.6
0.8
1
ideal0°50°71°100°
b)
0 50°
fieldangle
solid: tandashed: sag
100°
40 cyc/mm60 cyc/mm
10 cyc/mm20 cyc/mm
0
0.2
0.4
0.6
0.8
1c)
100%
y
-100% 0
Photographic Lens
Contax TVS
Ref: H. Zügge
Handy Phone Objective lenses
Examples
Ref: T. Steinich
US 7643225L = 4.2 mm , F'=2.8 , f = 3.67 mm , 2w=2x34°
US 6844989L = 6.0 mm , F'=2.8 , f = 4.0 mm , 2w=2x31°
EP 1357414L = 5.37 mm , F'=2.88 , f = 3.32 mm , 2w=2x33.9°
Olympus 2L = 7.5 mm , F'=2.8 , f = 4.57 mm , 2w=2x33°
1. Sampling of the field pixel by pixelSignal digitized in the time domain
2. Activ: Flying spot scanningPoint wise scanning of illumination, often by laser beamApplications: - bar code reader
- confocal microscopy- laser radar
(e.g. optical coherence tomography)
3. Passiv: Remote sensingDecomposition of object signal into pixelsApplications: - Night Vision
- monitoring, surveying- missile tracking
Scan Systems
Source: http://www.zamisel.com/SSpostavka2.html
Confocal
Wide Field
Scan Systems: Introduction
Scan resolution:Number of resolvable points in the field of viewcorresponds to angle resolution
Information capacity:1. Resolvable points2. Speed of scanning
Etendue: product of scan range andscanner area
λθ⋅⋅
== max2 ExP
Airy
DD
LN
log ∆θ
log v
angleresolution
scan speed
growing scancapacity
acoustic optical modulator
polygonmirror
galvoscanner
holographicscanner
electroopticalmodulator
resonantgalvoscanner
maxθθ ⋅=⋅ ExPMirMir DD
Deflecting Components
Different types of deflecting elements
Scanning
Non-Mechanical Deflection
Electro-optic EOD
Acousto-optic AOD
Mechanical
Oszillation
Galvanometric Galvoscanner
Holographic Holographic Scanner
Electrostatic MEMS Scanner
Rotation
Polygon Polygon-scanner
Rotating Prisms Dove Prism
Translation Lenses and lens arrays
Deflecting Components: Polygon Mirrors
Rotating mirror with plane facets Pyramidal
Prismatic
scanline
objectivelens
prismaticpolygon
scan line
pyramidalpolygon objective
lens
Galvanometer and Electrostatic Scanner
Galvo scanner MEMS-Scanner
Source: scanlab.de Source: researchgate.net
Scanner Lenses
Ideal scanner lens (F-θ lens): h = f θ Flat-field corrected lens: h = f tanθ
nonlinear displacement: distortion correction needed
42
Source: thorlabs.com
Example: Scanner Lens
Scan angle 2x30°
Monochromaticdiffraction limited
F-θ-corrected
0° 5° 10°
20°
15°
24° 28° 30.4°
USP 4436382:
43
Ref: B. Böhme