 A. An optical instrument that uses a lens or combination of lenses to magnify and resolve the fine details of an object

 A. Virtual image › i. Can only be seen by looking through a lens and cannot be viewed directly  B. Real image › Can be viewed directly

 A. Magnifying glass › i. Magnification of 5-10 times › Ii. Single lens

 i. Magnification up to 1500 times  Ii. Multiple lenses  Iii. Objective lens › 1. lower lens of a microscope that is positioned directly over the specimen  Iv. Eyepiece lens › 1. lens of a microscope into which the viewer looks, same as ocular lens

 1. base – support on which instrument rests  2. arm – C-shaped /handle/support  3. stage – horizontal plate upon which specimens are placed for study

 4. body tube – hollow tube on which objective and eyepiece are mounted at opposite ends  5. coarse adjustment – focuses lenses  6. fine focus – focuses but on smaller magnitude

 i. Illuminator › 1. transmitted illumination – light that passes up from condenser and through specimen › 2. vertical or reflected illumination – illumination of a specimen from above

 Ii. Condenser – collects light rays from illuminator and concentrates them onto specimen  Iii – objective lens – lens closest to specimen › 1. most microscopes are parfocal – when an image is focused with one objective in position, the other objective can be rotated into place and then the field will remain in focus

 Iv. Eyepiece or ocular lens › 1. monocular – one eyepiece › 2. binocular – two eyepieces

 D. Magnifying power › 1. total power = power of objective lens times power of eyepiece lens

 i. The ability of an objective lens to resolve details into separate images instead of one blurred image is directly proportional to the numerical aperture  Ii. Ex. A lens with a NA of 1.30 can separate details that are twice as close as compared to lens with NA of 0.65

 i. Field of view › 1. the area of the specimen that can be seen after it is magnified › 2. as magnifying power increases, field of view decreases

 Ii. Depth of focus › 1. the thickness of a specimen entirely in focus under a microscope › 2. decreases as magnifying power increases

 A. Two compound microscopes combined into one unit  B. Uses a bridge incorporating a series of mirrors and lenses to join them  Very useful in forensic science when side- by-side comparisons are necessary

 D. Vertical or reflected illumination › i. Used when comparing bullets, cartridges, other opaque objects  E. transmitted illumination › i. Compare hairs or fibers

 A. Power of 10x to 125x  B. Can present a 3-D image of object  C. Formation of right side up image  D. Very frequently used in crime lab  E. Wide field of view and great depth of focus  F. Used often for examination of paint, soil, gunpowder residues, marijuana, etc.

 A. When a beam of light passes through certain types of substances, it emerges vibrating in only one plane  B. Plane-polarized light › i. Light confined to a single plane of vibration

 C. Polarizer › i. Device that permits passage of light waves vibrating in only one plane

 D. Second polarizing crystal – analyzer  E. Can modify stereo or compound microscopes so can detect polarized light  F. Application – study materials that polarize light ex. Birefringent substances

 A. An instrument that links microscope to a spectrophotometer  B. Spectrophotometer = an instrument used to measure and record the absorption spectrum of a chemical substance  C. Allows better comparison of substances

 A. Image is produced by aiming a beam of electrons onto the specimen and studying electron emissions on a closed TV circuit or computer  B. High magnification  C. High resolution

 D. High depth of focus  E. Used as tool for determining whether or not a suspect has recently fired a gun  F. X-ray analyzer