II From “Beam Paths” to the “Microscope” October 2008 Rudi Rottenfusser – Carl Zeiss...
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Transcript of II From “Beam Paths” to the “Microscope” October 2008 Rudi Rottenfusser – Carl Zeiss...
IIII
From “Beam Paths” to the “Microscope”From “Beam Paths” to the “Microscope”
October 2008October 2008
Rudi Rottenfusser – Carl Zeiss MicroImaging
Understanding Beam Paths
From Pin Hole Camera to the Lens The three “Thin Lens Laws” Image Ratio – not the same as Magnification “Magnification” The Concept of “Infinity” The “simple” microscope (Leeuwenhoek, Magnifier,
Eyepiece) The “compound” microscope – Upright / Inverted Illumination – Transmitted / Reflected Stereo Microscopes – Greenough / Telescope Types
Geometric Optics – Creating an Image
The Pinhole Camera
Geometric Optics – Creating an Image
Making the aperture larger…
Geometric Optics – Creating an Image
Adding a lens…
How does a lens “bend” light?
Infinite number of prisms with different angles
Drawing Beam Paths
• Thin Lens Laws (1,2,3)
1) Draw ray through center of lens
n1 n2
(small error is ignored if glass is very thin)
Exactpath
2) Rays that enter the lens parallel to the optical axis cross over at Back Focal Point
(Back) FocalPoint
2b) Rays that enter the lens from infinity, cross over at Back Focal Plane
(Back) FocalPlane
3) Light rays that enter the lens from the focal point exit parallel to the optical axis.
(Front) Focal Point
ffocal distance
3b) Light rays that enter the lens from a point along the focal plane exit parallel ().
Size translates to angle !
Predicting the behavior of imaging systems
(principle ray technique)
ff
Object
Back Focal PtFront Focal Pt
1) Draw in central ray
Object
1) Draw in central ray
2) In parallel; out via back focal point
1) Draw in central ray
2) In parallel; out via back focal point
3) In via front focal point; out parallel
1) Draw in central ray
2) In parallel; out via back focal point
3) In via front focal point; out parallel
Intersection defines image
Image
BA
Lens) Object to of (DistanceA
Lens) toImage of (Distance B
Object of Size
Image of Size Ratio Image
Our eye is a great imaging system.
Its lens provides variable focal lengths
to bring objects in focus at the retina
Objects appear to the eye at different magnifications, depending on their distance from the eye. Accommodation (lens) makes it possible.
MB ~ 2x MA
A B
Magnification – unaided Eye
Conventional Viewing Distance
250 mm
1x
?
“Magnification” 1x
f = 250 mm
1x
1x
250 mm
“Infinity Optics” ?
Higher Magnifications via Single Lens
f = 250 mm
1x
Example: f=50mm
5x
Magnifying Glass (Loupe) Lensf
mmM
250
The Leeuwenhoek
microscope
Intermediate Image Eyepoint (Exit Pupil)
The Eyepiece (Ocular) is a “Simple” Microscope
If you need a magnifier, remove eyepiece, turn upside down and move close to eye;
subject will be about 25mm away from lens
M
mmfEyepiece
250
Objective
Eyepiece
The
Compound Microscope
Specimen
Intermediate Image
Eye (Retina)
Tube lens
Objective
Eyepiece
The
Compound Microscope
Specimen
Intermediate Image
Eye (Retina)
-corrected
Infinity Space
Advantage of Infinity Correction
Infinity System
Specimen off-center
Finite System
Specimen off-center
ax
lat.
Intermediate image is
1) “in registration”2) fully corrected
Objective
The -corrected Compound Microscope
Eyepiece
Tube
Objective f
250mm
250mm
f
f
250mmM
EyepieceObjectiveMicroscope Compound M MM
Objective
Eyepiece
EyepieceObjective
Tube
f
250mm
f
fM
Tube Lens
Cross-section through an ∞ corrected Microscope
Intermediate image (fully corrected)
Infinity Space
Objective
Tube Lens
Eyepiece
Upright microscope.
Inverted microscope
The basic light microscope types
Illuminating the Specimen
Transmitted Light
The sample must be transparent !
Upright microscope.
Inverted microscope
Eg. Fluorescence, Opaque Samples
Illuminating the Specimen
Reflected (Incident) Light
Upright microscope.
Inverted microscope
Upright microscope.
Inverted microscope
Mixed Illumination
Which Microscope types typically use these types of illumination?
External Sources, e.g.
Fiber Optics
Reflectors
Ring Lights
Various Combinations
Source
?
“Couldn’t one build a microscope for both eyes, and thereby generate spatial images?”
Question addressed to Ernst Abbe in 1896
by Horatio S. Greenough
1896: Drawing by Horatio S. Greenough
1897 – the first Stereo Microscope in the world, built by Zeiss according to the “Greenough” principle
Greenough Type
What happens if we take the objective away from the microscope?
Tube lens
(Zeiss: f=164.5mm)
Objective
Eyepiece
Eyepiece
Tube
f
fTelescopeM
Eyepiece
Tube
f250mm
250mm
fM
We have created a “Telescope”
∞
∞
Greenough Type
Telescope Type Introduced first by Zeiss - 1946
Comparison
Greenough Type:
• 2 separate beam paths going through centers of lenses
• Excellent correction
• Economical
Telescope Type:
• One common objective for both beam paths
• Flexibility to interchange tubes and objectives
• Possibility to add intermediate tubes e.g. for Fluorescence, Co-observation, Drawing
Questions? Short break?
Next:
Dissecting an infinity-corrected microscope