Reflection! Reflection and Virtual Image!

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Horatio Norman
5 years ago
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- particle theory: travel close, bounce from different pts, reverse order - texture of surface => specular vs.

1 1/30/14 Reflection - wave hits non-absorptive surface surface of a smooth water pool - incident vs. reflected wave law of reflection - concept for all electromagnetic waves - wave theory: reflected back to front at angle determined by incident angle - particle theory: travel close, bounce from different pts, reverse order - texture of surface => specular vs. diffuse reflection Reflection and Virtual Image - formation of a virtual image (mirror image) behind mirror does not exist light rays don t pass through it, could not be projected onto screen - image is the same size as original - upright 1

1/30/14 Light reflecting of a flat mirror is one thing

Spherical Mirrors plane yet not so so simple - piece

with R = radius of curvature - ray diagrams = 3 rays (2

through focal point (F) 2nd: tip of object through

2 1/30/14 Light reflecting of a flat mirror is one thing but reflecting off a spherical mirror is another story Spherical Mirrors plane yet not so so simple - piece cut out of sphere - focal point = 1/2 distance F = R/2, with R = radius of curvature - ray diagrams = 3 rays (2 are necessary) 1st: tip of object, parallel then through focal point (F) 2nd: tip of object through curvature center (C) 3rd: parallel to first from bottom of object C F 2

1/30/14 Spherical Mirrors Concave = converging mirror - image is inverted - when object beyond center of curvature C => image between focal pt (F) and C I C O F O F

light through pathways of optical systems and onto specimen - flat mirrors for folding light at precise angles with minimum distortion - What mirrors are used in

3 1/30/14 Spherical Mirrors Concave = converging mirror - image is inverted - when object beyond center of curvature C => image between focal pt (F) and C I C O F O F C Convex = fish eye/diverging mirror - reflective surface bulges towards light - F and C = imaginary - image diminished and upright Mirror Application - directing light through pathways of optical systems and onto specimen - flat mirrors for folding light at precise angles with minimum distortion - What mirrors are used in microscopy? - darkfield: paraboloidal mirror cone illumination at high numerical aperture - DIC: direct light through objective - FLM: dichroic mirror or beamsplitter 3

$1/30/14 Refraction - when light passes from one medium into another refraction = manifested in bending of light - object submersed in water$ $Angles n (refractive index) = c/v where c=speed of light; n=velocity of light - RI vacuum = 1, air = 1.$ $resolve depends on refractive index - determines the focal length of objective - refractive indices: Air = 1.003 Water = 1.$

4 1/30/14 Refraction - when light passes from one medium into another refraction = manifested in bending of light - object submersed in water and mirages in the desert - important characteristic of microscope lenses - refractive index = law of the ratio of incident and refracted Angles n (refractive index) = c/v where c=speed of light; n=velocity of light - RI vacuum = 1, air = higher index, slower speed of light - relationship between bending angles and waves Refraction and Microscopy - ability to magnify and resolve depends on refractive index - determines the focal length of objective - refractive indices: Air = Water = 1.33 Immersion Oil = Crown Glass = exact RI varies with color of light ability of prism to separate colors Image made by single lens can therefore suffer aberrations => multi-lens systems 4

5 1/30/14 Aberrations Chromatic aberration: different colors (wavelengths) focus at different distances Coma: resulting in the images of structures out from the center being smeared outwards Spherical aberration: resulting in light passing through lens center being focused at different distance to light passing through the outer portion Diffraction - light is never known to follow crooked passages nor to bend into the shadow Sir Isaac Newton particles of light travel in straight lines objects in the path of light will cast shadows - when passing close to edge of an object (i.e. slit, aperture) = spreading at oblique angle => DIFFRACTION, similar to dispersion 5

$1/30/14 Diffraction and Microscopy - image composed of overlapping points of light from specimen$ $= straight line large wavelength = diffraction of bright center and darker circles around it$ $Diffraction and the Airy Disk - diffraction causes patter with a bright central area = primary$ $aperture = microscope, human eye similar pattern: bright disk surrounded by diffraction rings -$

6 1/30/14 Diffraction and Microscopy - image composed of overlapping points of light from specimen plane - image forming light rays are diffracted point seen as diffraction pattern - image never exact representation - importance of apertures = size determines reaction of light small wavelength = straight line large wavelength = diffraction of bright center and darker circles around it Diffraction and the Airy Disk - diffraction causes patter with a bright central area = primary maximum - bounded on each side by secondary maxima separated by dark areas = minima - circular aperture = microscope, human eye similar pattern: bright disk surrounded by diffraction rings - proper focus: light intensity at lowest minimum is 0 no matter how perfect, secondary diffraction maxima and central spot remain 6

1/30/14 Resolution and Abbe s Equation = ability to discriminate between 2 pts - used to calculate approximate resolving power resolving power = wavelength of light/2 - also affecting resolving power

7 1/30/14 Resolution and Abbe s Equation = ability to discriminate between 2 pts - used to calculate approximate resolving power resolving power = wavelength of light/2 - also affecting resolving power may be numerical aperture (NA) = light striking specimen gets bent (finer details = increased angle of bending) = image forming rays = the more image forming rays gathered the better the image NA = expression of the ability of an objective to collect these image forming rays; the large the NA, the better able the objective Numerical Aperture NA => Dimensionless number that characterizes the angle of light accepted into lens 7

1/30/14 Compensation: Lens - combat defect/ produce sharp images = complex lenses achromat apochromat plan achromat - achromat = corrected for red and blue,

often 4 colors In Student Microscopes high degrees of corrections Plan C (plan achromatic) spherical chromatic = more than 4 colors generally 11 lens

8 1/30/14 Compensation: Lens - combat defect/ produce sharp images = complex lenses achromat apochromat plan achromat - achromat = corrected for red and blue, 65% flat - apochromat = corrected for three colors, 80% flat - plan achromat = corrected for spherical aberration, 95% flat highest degree of correction, often 4 colors In Student Microscopes high degrees of corrections Plan C (plan achromatic) spherical chromatic = more than 4 colors generally 11 lens elements = lens triplet (3 lens sets with multiple lenses) plus front and back cover lenses Back cover = generally planar, front cover = 95% flat, minimal curvature 8

1/30/14 Compensation: Filters - Absorbing/reflecting filters => remove

com/primer/java/filters/absorption/index.

microscope Color correction filters not currently used in microscopy

9 1/30/14 Compensation: Filters - Absorbing/reflecting filters => remove chromatic aberrations problem: filter out all colors but one Not used in current microscope Color correction filters not currently used in microscopy => white correction Neutral density filters decreasing light intensity not currently used in microscopy => through computer settings 9

The Nature of Light. Light and Energy

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