microscopes

Focus – use both eyes and lowest objective to find the specimen. Once in view, close left eye and use
right eye fine focus until sharp, then close right eye and use left eye, if specimen is not sharp then adjust
with left ocular ring, do not use the fine focus knob on the arm of the microscope. This is the Diopter
adjustment, which allows for differences in the strength of vision between left and right eyes.
Interpupillary adjustment – slide oculars apart as needed to adjust for width of pupils, if correctly set
only one image should be seen when viewing a sample with both eyes (no double vision).
Total magnification = ocular magnification X magnification of objective lens being used.
Example: 10x ocular X 40x objective lens = 400x total magnification of specimen.
Only use lens paper to clean the ocular or objective lenses.

Terminology
Light microscope = microscope that uses light and lenses to magnify a specimen for viewing
Compound microscope = microscope that uses two lenses - an objective lens with a very short focal
length and an eyepiece (ocular lens) with a longer focal length, mounted in the same tube.
Parfocal = image stays roughly in focus when magnification/focal length is changed. Should only need to
use the fine focus knob to adjust when changing the objective lens
Parcentric = image stays centered when magnification/objective lens is changed.
Depth of field = range of distance that where the specimen can move and still be viewed without
negatively affecting the clarity of the object under observation. The lower the lens magnification the
greater the depth of field.
Field of view = the areas that is visible through the microscope; the lower the magnification of a lens the
greater the field of view.
Working distance = distance between the objective lens and the mechanical stage.
Histological stains = dyes that preferentially bind cellular components to increase contrast and hence
increase resolution.
Basic stains are dyes have a net positive charge and bind to components of cells and tissues that
are negatively charged. Examples = methylene blue, crystal violet, and hematoxylin.
Phosphate groups of nucleic acids (DNA and RNA)
Sulfate groups of some polysaccharides (glycosaminoglycans) and some proteins
(mucus).
Acidic stains have a net negative charge and bind to components of cells and tissues that are
positively charged. Examples = eosin, Congo red, acid fuschin.
Ionized amino groups in proteins (side chains of lysine and arginine).
Resolution = the minimum distance at which two distinct points of a specimen can still be seen as
separate entities.
Magnification = refers to the amount or degree of visual enlargement of an observed object.
Always start with lowest objective, greatest field of view and depth of field; always center specimen
before moving up in magnification.
The image you view is inverted (upside down and backwards) compared to it’s orientation on the slide.