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