scopes have a minimum of two magnifying lenses (ocular and objective lenses)
Monocular
one eyepiece
Binocular
two eyepieces
Light microscopy
source of illumination is visible light from a lamp
Darkfield microscopy
utilizes the blocking out of central light so only oblique rays pass through the specimen. Advantages: good for outlining outlines, edges, and boundaries. Disadvantages: is very wasteful of light, slides must be very clean, and slides must be a standard thickness and of identical types of glass.
Phase-contrast microscopy
makes unstained phase objects (which don't absorb light) yield contrast images as if they were amplitude objects by shifting the direct light ¼ of a wavelength. Advantage: improves contrast for thin, living, and unstained materials. Disadvantage: phase halos, reduction in resolution, cannot use thick specimens.
Nomgrgki microscopy
one side of a detail of the specimen appears bright, while the other side appears dark. This shadow effect is pseudo 3-dimensional. It is used for similar specimens as are used in phase microscopy. Resolution and color are better, but it is much more expensive.
Stereoscopic (dissecting) microscopy
has low magnification and is used for viewing and manipulating relatively large objects. The depth of field is greater than In the light microscope, and the light source can be manipulated allowing viewing of objects which are too thick to transmit light.
Electron microscopy (EM)
can magnify objects up to 1,000x greater than the light microscopy - ie: up to about a million-fold. It has much greater resolution than a light microscope. Electrons are the source of illumination
Interpupillar distance
distance between the oculars
Working distance
distance between the specimen and objective lens
Parfocal lens
little refocusing is required when changing the lens as the focal points of all the objective lens are the same distance from the ocular lens(es).
Depth of field
the range in the depth of the sample that all appear to be in focus.
Resolving Power (d)
d= (0.61 λ)/(n sin α), where
λ = wavelength (400 nm avg for visible light and 0.05 Å for electrons.
n= refractive index (1.0 for air and 1.6 for oil)
α = ½ the angle of illumination from the speciment as controlled by the substage iris.
Magnification
to compute, multiply the magnification of the ocular lens by that of the objective lens.