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Transcript
II From “Beam Paths” to the “Microscope” October 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 (small error is ignored if glass is very thin) n1 n2 Exact path 2) Rays that enter the lens parallel to the optical axis cross over at Back Focal Point (Back) Focal Point 2b) Rays that enter the lens from infinity, cross over at Back Focal Plane (Back) Focal Plane 3) Light rays that enter the lens from the focal point exit parallel to the optical axis. f focal distance (Front) Focal Point 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) Back Focal Pt Front Focal Pt f Object f 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 A B Image Intersection defines image Image Ratio Size of Image B (Distance of Image to Lens) Size of Object A (Distance of Object to Lens) Our eye is a great imaging system. Its lens provides variable focal lengths to bring objects in focus at the retina Magnification – unaided Eye MB ~ 2x MA A B Objects appear to the eye at different magnifications, depending on their distance from the eye. Accommodation (lens) makes it possible. Conventional Viewing Distance ? 250 mm 1x “Magnification” 1x 250 mm 1x f = 250 mm 1x “Infinity Optics” ? Higher Magnifications via Single Lens 1x f = 250 mm Magnifying Glass (Loupe) M 5x Example: f=50mm 250mm f Lens The Leeuwenhoek microscope The Eyepiece (Ocular) is a “Simple” Microscope f Eyepiece Intermediate Image 250mm M Eyepoint (Exit Pupil) If you need a magnifier, remove eyepiece, turn upside down and move close to eye; subject will be about 25mm away from lens Eye (Retina) Eyepiece Intermediate Image The Compound Microscope Objective Specimen Eye (Retina) Eyepiece Intermediate Image The -corrected Compound Microscope Tube lens Infinity Space Objective Specimen Advantage of Infinity Correction Dlat. Intermediate image is Dax 1) “in registration” 2) fully corrected Objective Finite System Infinity System Specimen off-center Specimen off-center The -corrected Compound Microscope Eyepiece M f Tube 250mm 250mm f Objective 250mm f Eyepiece M Tube Lens f Tube f Objective 250mm f Eyepiece M Compound Microscope M Objective M Eyepiece Objective Cross-section through an ∞ corrected Microscope Eyepiece Tube Lens Infinity Space Objective Intermediate image (fully corrected) The basic light microscope types Upright microscope . Inverted microscope Illuminating the Specimen Transmitted Light The sample must be transparent ! Upright microscope . Inverted microscope Illuminating the Specimen Reflected (Incident) Light Eg. Fluorescence, Opaque Samples Upright microscope . Inverted microscope Mixed Illumination Upright microscope . Inverted microscope 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? Eyepiece ∞ Tube lens ∞ Objective M (Zeiss: f=164.5mm) f Tube 250mm 250mm fEyepiece M Telescope f Tube f Eyepiece 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, Coobservation, Drawing Questions? Short break? Next: Dissecting an infinity-corrected microscope