FOS 706 Introduction to Microscopy Fall 2023 PDF

THE MICROSCOPE FOS 706 Frequently the first tool of choice in the forensics lab. INTRODUCTION TO MICROSCOPY 1 Wide applicability to forensics analyses, physical evidence problems. 2 THE MICROSCOPE n n Refraction An optical instrument that utilizes one or more lenses to magnify and resolve...

THE MICROSCOPE FOS 706 Frequently the first tool of choice in the forensics lab. INTRODUCTION TO MICROSCOPY 1 Wide applicability to forensics analyses, physical evidence problems. 2 THE MICROSCOPE n n Refraction An optical instrument that utilizes one or more lenses to magnify and resolve the fine details of the object under study. Magnified image: refraction of light rays through the lens. 3 n n 4 Refraction 5 Refraction is defined as the bending of light as it travels from one material into another material. Light slows down when it refracts. Refraction: Converging Lens 6 1 Lens Focal Length Image Formation by a Converging Lens https://www.physicsclassroom.com/Class/refrn/u14l5c1.gif http://www.diracdelta.co.uk/science/source/f/o/focal%20length/source.html#.V-CgOTaDDHg 7 8 Ideal Lens Equation SIMPLE MICROSCOPE 1 1 1 = + ! ! ! n f = lens focal length p = object distance q = image distance != A magnifying lens is a “simple microscope” capable of 5X-10X magnification; produces a “virtual image” ! ! where m = magnification, when q>p if q<p, instead of m, use r = reduction 9 10 Formation of a Virtual Image with a Simple Lens VIRTUAL IMAGE The magnified image appears to be on the same side of the lens as the object being magnified. q p Lens Virtual Image Principal Focus Object f Ideal Lens Equation: 11 Principal Focus f 1 1 1 = + f p q 12 2 Formation of a Real Image with a Simple Lens REAL IMAGE n n n n magnified image appears on the side of the lens opposite the object being magnified image is inverted can be seen directly can be projected onto a screen. p q Lens Principal Focus Object Principal Focus Real Image f f Ideal Lens Equation: 13 14 Image Formation with Converging Lenses THE COMPOUND MICROSCOPE n n n http://micro.magnet.fsu.edu/primer/java/len ses/converginglenses/index.html n n n 15 1 1 1 = + f p q AKA The Biological Microscope Magnified image is formed by two lenses mounted at each end of a hollow tube The objective lens creates a real inverted magnified image. The ocular lens produces a magnified virtual image of the real image. Magnifications up to 1500X possible 16 MECHANICAL SYSTEM n n n n n n 17 = support structure Base - supports the instrument Arm - C-shaped upright structure hinged to base - supports microscope - acts as handle for carrying Stage - platform on which sample is placed for examination; sample is mounted on glass slide Body Tube - hollow tube on which lenses are mounted Coarse & Fine Adjustment - Knobs focus lens by raising or lowering the body tube or stage 18 3 OPTICAL SYSTEM MECHANICAL SYSTEM Head (Body Tube) n Turret Arm n Stage n Coarse Focus n Fine Focus Base http://www.lehmanscientific.com/p_o-bh2.html Substage Rack & Pinion 19 n Illuminates, magnifies and resolves the detail of the object under examination Illuminator - provide light source n Transmitted illumination n Reflected illumination Condenser - collects light rays from base illuminator and concentrates them on the sample Objective Lens - lens closest to specimen - can have several mounted on revolving nosepiece Ocular - lens closest to eye - monocular and binocular 20 TOTAL MAGNIFICATION OPTICAL SYSTEM Oculars Total magnification = objective magnification X ocular magnification Objective Substage Condenser Aperture Diaphragm/ Substage Diaphragm Field Diaphragm Lamp 21 22 MICROSCOPE TYPES n n n n n Stereoscopic Microscope Stereoscopic Microscope Comparison Microscope Polarizing Light Microscope Microspectrophotometer Electron Microscope n n n n n 23 Primary screening tool; searching for trace evidence Two separate monocular compound microscopes, each having two lenses Provides a 3D image with 10X to 125X magnification Provides right side up view of object Large working distance: useful for bulky evidence 24 4 Comparison Microscope n n n n Polarizing Light Microscope Two compound microscopes attached by an optical bridge Allows side-by side comparisons Binocular eyepiece see half of each microscope sample Study bullet striations, hair 25 n What is plane polarized light? Ordinary light vibrates in every direction perpendicular to its direction of travel. n Plane polarized light vibrates in one direction perpendicular to its direction of travel. n 26 Polarizing Sunglasses http://www.micro.magnet.fsu.edu/optics/lightandcolor/polarization.html http://www.microscopyu.com/articles/polarized/polarizedlightintro.html 27 28 Polarizing Light Microscope n n Polarizing Light Microscope Polarizer - confines light to a single plane of vibration; mounted in-between light source and specimen Analyzer = a 2nd polarizer; used to detect polarized light; placed between objective lens and http://www.microscopyu.com/articles/polarized/polarizedintro.html ocular lens n n Alignment of polarizer & analyzer = parallel or “crossed” Used to study materials that “polarize” light: crystalline mat’l, minerals, fibers http://www.microlabgallery.com/gallery/Cotton1Ac.aspx 29 http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/pages/cotto nsmall.html 30 5 Microspectrophotometer n n n = Microscope + Spectrophotometer. Microscope: search and locate minute traces of physical evidence. Spectrophotometer: allows characterization of the chemistry of the evidence based upon its selective absorption spectras. http://www.micro.magnet.fsu.edu/optics/lightandcolor/polarization.html 31 32 Microspectrophotometer Electron Microscope n n http://www.mikroskop-spektroskopie.de/Home/?STLWEB=en http://www.madatec.com/Smiths_de t_file/IlluminatIR.pdf 33 34 Electron Microscope n n n n 35 Uses an electron beam to view a specimen Magnified image produced by aiming an electron beam on the specimen, which causes the specimen to release characteristic electrons, which can then be collected, converted to an electronic signal, amplified and displayed on a screen. Electron Microscope Uses electromagnetic lenses instead of glass lenses Signal displayed on a computer screen High magnification >500,000X with high resolution Very expensive n n Can also be used to study elemental composition of specimen using X-ray production (requires an X-ray analyzer) Gunshot Residue 36 6 Electron Microscope http://www.jeol.com/Portals/0/prodshots/eo/jsm-6700f.jpg 37 7