Microscopes
Anton van Leeuwenhoek and his Microscope
Parts of the Microscope
head
ocular
arm
rotating nose piece
objective lens
mechanical stage
course adjust
stage
condenser
mechanical stage controls
light source
fine adjust
base
Power switch and light control locations vary.
How an
image is
formed by a
microscope
Working distance
Working distance is the distance between
the specimen and the magnifying lens.
Depth of field
Depth of field is a measure of the amount of
a specimen that can be in focus.
Magnification
Magnification is a ratio of the enlargement
(or reduction) of an image (drawing or
photomicrograph), usually expressed as
X1, X1/2, X430, X1000, etc.
Magnification and resolution are terms used
frequently in the study of cell biology, often
without an accurate definition of their meanings.
Resolution
Resolution is the ability to distinguish
between two points. Generally resolution
increases with magnification, although
there does come a point of diminishing
returns where you increase magnification
beyond added resolution gain.
How an
image is
formed by a
microscope
How the image appears
Determining field size
As the total magnification goes up, field size gets smaller.
You can measure field size directly at low magnification.
However, at higher magnification you won’t have a sufficiently precise
measuring instrument. So then what?
You can calculate field size from what you know about the
relationship between field size and magnification.
Calculating field size
Diameter of field A (known from direct measurement) X Total magnification of field A
= diameter of field B (this is the unknown) X total magnification of field B
You can rearrange the terms to produce the following equation:
diameter of field A X total magnification of field A = diameter of field B
total magnification of field B
Therefore:
If field A = 2 mm in diameter at 50X total magnification
And the total magnification of field B = 100X then
Diameter field B =
2 X 50 = 100 = 1 mm
100
100
But, there is another way!
The diameter of the field is inverse to the magnification!
(see slide11)
What this means is that if you increase the magnification by
say a factor of four (four times), the field size will decrease by
the same factor.
Example:
The field diameter at 100X is 2 mm.
Go from 100X to 400X, an increase of 4 times.
The field diameter is decreased 4 times. (Simply divide by 4!)
2 mm = 0.5 mm
4
Illustrations of microscope
observations
Drawings of specimens observed under the microscope should
always include the following:
• Title
• Total magnification
• Labels of interesting features
Example of a proper illustration
plasma membrane
nucleus
Epithelial cells from a cheek
Total magnification - 400X
Parts of the Microscope
This is the model of
scope used in JH 219
Get to Work!