Transcript Slide 1
Ophthalmic Optical Instruments I
Telescopes and Microscopes
C. I. OPHTMALMOMETER, CHICAGO ILLINOIS ca 1899
TELESCOPES
Astronomical (Keplerian) Telescope
Image is Inverted
objective
eyepiece
Fe Fo
fe
fo
Virtual image
at 25 cm
M=-
fo
fe
Astronomical Telescope
objective
eyepiece
Fe Fo
fe
fo
Virtual image
at infinity
D
Galilean Telescope
plus
lens
negative
lens
fp’s
coincide
fp
fp
fp
final
telescope
parallel rays
MAGNIFICATION OF GALILEAN TELESCOPE
objective
eyepiece
fep
fobj
Example:
fobj
M=
fep
fobj = 50.0 mm
fep = - 5.0 mm
M=
50.0
= 10.0
- 5.0
GTT 04
Viewing Through a Galilean Telescope
object
parallel
rays
iImage
emmetropic
eye
UPRIGHT OBJECT APPEARS UPRIGHT
GTT 04
D
MICROSCOPES
ANGULAR MAGNIFICATION
Apparent size of object depends on angle it subtends at eye.
100 m
100 m
10 m
10 m
ANGULAR MAGNIFICATION
On average, an object cannot be closer than
25 cm from the eye to be seen clearly.
2 5 cm
Average distance of
most distinct vision
h
ta n
25
h
f
2 5 cm
virtu a l im a g e
’
h
h
ta n ’
f
f
2 5 cm
A n g u la r M a g n ifica tio n =
ta n ’
ta n
=
h
f
h
25
=
2 5 cm
f (cm)
Eye
BASIC
MICROSCOPE
magnifier
Eyepiece
f eyepiece
Real image
real image
magnification
Objective
Object
fobjective
MICROSCOPE
MAGNIFICATION
25
M2 =
f
Im
M1 =
Ob
Im X 25
Mtotal= Ob f
OBJECTIVES
Numerical Aperture (NA)
Light gathering ability
Resolution
NA = n sin a
D
w.d.
a
n
EXAMPLE
a = 14
n = 1.00 (air)
NA = 1.00 x sin(14 )
NA = 0.24
OBJECTIVES
N.A. Examples
a = 28
n = 1 .0 0
N A = 0 .4 6
a = 35
n = 1 .0 0
N A = 0 .5 7
a = 60
n = 1 .5 2 (o il)
N A = 1 .3 2
Huygens
EYEPIECES
(OCULARS)
Ramsden
parallel rays from
eyepiece
Real image
Real image
converging
rays from
objective
D
REAL MICROSCOPE
Real image
Objective
Specimen
EXPERIMENT 4
Basic Microscope
real image
on card
iris
diaphragm
onion skin
f
Produce real image of onion skin on card.
Mark distance of real image on base.
EXPERIMENT 4--CONTINUED
View real image with magnifier (“eyepiece”)
real
image
plane
f
Adjust iris diaphragm. How does image change?
25
What is the total magnification? M = Im X
total Ob f
Slit-lamp Biomicroscope
The slit-lamp
biomicroscope
begins with a
microscope….
Eyepiece
Objective
Specimen
….turned on its side
….change specimen, objective & eyepiece
subject
Huygens
eyepiece
objective
image
plane
…….fundamental slit-lamp biomicroscope
Build in magnification change without changing
working distance
working
distance
fobj
Galilean
telescope to
change mag
no image in
image plane
Build in magnification change without changing
working distance
working
distance
fobj
Galilean
telescope to
change mag
no image in
image plane
D
…..add lens to form image in eyepiece
image plane
astronomical
telescope
D
Porro* prism
2 right-angle prisms
F
1800 image rotation
displace image
horizontally
reduce length of
telescope
F
Porro. 1801 – 1875.
Italian optical instrument maker
*Ignazio
Porro -Abbe
Slit-lamp with folded optical path
D
D
binocular slit-lamp viewing system
Operating Microscope
Operating microscope optics are
very similar to those of the slit-lamp.
Change
magnification
without
changing
working
distance
binocular
astronomical
telescopes
magnification change:
Galilean telescopes
prism
objective lens
Specular Microscope
specular == “mirror-like”
Useful in seeing corneal endothelial cells
Endothelial cells posterior surfaces flat &
adjacent to aqueous
Difference in index of refraction gives
specular reflection
Specular Microscope
halogen lamp
condenser
dipping
cone
objective
slit
lens
M
Ramsden
eyepiece
D
film
or
CCD
endothelium
slit image
{
specular reflections and stray light
Typical image of endothelium
from specular microscope
Confocal Principle
Red cell in thick sample
imaged by lens
Pinhole in image plane
passes all light from blue cell
Blue cell, nearer to surface,
imaged at different point
Pinhole blocks most of light
from red cell
Based on Webb, RH, Rep Prog Phys 59:427
Confocal Principle
Point source CONFOCAL with
blue cell & pinhole selectively
illuminates blue cell
Confocal point source gives
less light to red cell, and most is
blocked by pinhole
Beam splitter makes confocal
microscope epitaxial
Based on Webb, RH, Rep Prog Phys 59:427
Confocal Optical Systems:
Pinhole allows light
from small volume in
sample. Other stray
light blocked.
Confocal point source
confines light to small
volume in sample.
Rejects stray light
Allows Z-axis “sectioning”
Confocal systems can improve imaging
Standard specular
microscope
Confocal specular
microscope
Koester’s confocal microscope
CCD camera
M
lamp
M
confocal
slit
slit
rotating
mirror
Koester’s
Confocal
scanning
microscope
objective
specimen
Other Scanning Methods and
Confocal Microscopes
Tandem Scanning Confocal Microscope
Scanned (laser) Spot Confocal Microscope
Scanned Slit Confocal Microscope
Tandem Scanning Confocal Microscope
Uses Nipkow disk
Paul Nipkow (1860 -1940)
Studied with Helmholtz
r
Invented disk in 1883
Used for telegraphing pictures
Later used in 1st television
Sets of holes in plate
Holes on Archimedes spirals
r = a + b
D
Petran Tandem
Confocal
Scanning
Microscope
Very light
inefficient
TCSM for imaging cornea
X-Y mirror
confocal
laser
scanning
Confocal slit
scanning
3-D reconstruction from confocal images
dfiber from subepithelial plexus
Guthoff et al. Cornea 24:608
Commercial Confocal Scanning Corneal
Microscopes
Nidek
Confoscan
Heidelberg HRT
II*-Rostock
attachment
*also scans retina
Topcon SP2000p