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Optical microscopyOptical microscopy
OpticsLenses and image formationDepth of fieldNumerical apertureResolutionInstrumentSpecimen preparationContrastExamples
OpticsLenses and image formationDepth of fieldNumerical apertureResolutionInstrumentSpecimen preparationContrastExamples
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Optical microscopyOptical microscopy
Index of refraction
=
Index of refraction
= velocity of light in airvelocity of light in air
velocity of light in other mediumvelocity of light in other medium
Snell's law
=
Snell's law
= sin isin isin rsin r airair
mediummedium
Optical microscopyOptical microscopy
Refraction makes lenses possible
Converging or positive lens
Refraction makes lenses possible
Converging or positive lens
Optical microscopyOptical microscopy
For diverging or negative lens, focal point on other side of lens
Greater lens curvature ––> shorter focal length
For diverging or negative lens, focal point on other side of lens
Greater lens curvature ––> shorter focal length
Optical microscopyOptical microscopy
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Optical microscopyOptical microscopy
Image formation in lens systemImage formation in lens system
Optical microscopyOptical microscopy
Numerical aperture = N.A. = sine of half the angle over which light enters objective lens.Numerical aperture = N.A. = sine of half the angle over which light enters objective lens.
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Resolution = /2N.A.Resolution = /2N.A.
Optical microscopyOptical microscopy
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Optical microscopyOptical microscopy
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Optical microscopyOptical microscopy
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Optical microscopyOptical microscopy
field diaphragm
condenser lens
half silvered mirrors
eyepiece
eye
projector lens
photographic plate
specimen
objective
light source
REFLECTED LIGHT MICROSCOPE
(5X, 10X, 20X, 50X, 100X)
(5X, 10X)
image display
Optical microscopyOptical microscopy
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CONTRAST IN THE REFLECTED LIGHT MICROSCOPE
1. Different phases may be delineated due to differences in reflectivity. Reflectivity varies with wavelength, so contrast may be changed through insertion of a filter.
2. Crystals of different orientations are etched at different rates. Results in contrast due to ledges formed at grain boundaries.
3. Etchants frequently attack grain boundaries preferentially leading to grain boundary grooving.
CONTRAST IN THE REFLECTED LIGHT MICROSCOPE
1. Different phases may be delineated due to differences in reflectivity. Reflectivity varies with wavelength, so contrast may be changed through insertion of a filter.
2. Crystals of different orientations are etched at different rates. Results in contrast due to ledges formed at grain boundaries.
3. Etchants frequently attack grain boundaries preferentially leading to grain boundary grooving.
Optical microscopyOptical microscopy
CONTRAST IN THE REFLECTED LIGHT MICROSCOPE
4. Etchants may facet the grains. The faceting is different for differently oriented grains.
5. Etchants often attack different phases at different rates. Leads to surface relief.
6. Some etchants stain the sample surface so that differently oriented grains and different phases take on varied colors.
CONTRAST IN THE REFLECTED LIGHT MICROSCOPE
4. Etchants may facet the grains. The faceting is different for differently oriented grains.
5. Etchants often attack different phases at different rates. Leads to surface relief.
6. Some etchants stain the sample surface so that differently oriented grains and different phases take on varied colors.
