1. Ocular--provides initial magnification of the object--usually
10X.
2. Draw tube--the ocular fits into the draw tube, whose length
separates the ocular from the objectives by the proper distance.
3. Revolving nosepiece--allows the objectives to be changed by
revolving them into working position.
4. Objectives--provide secondary magnification of 10X, 20X and 40X.
5. Stage--the place where the slide rests for viewing under the
microscope.
6. Clips--holds the slide securely on the stage.
7. Diaphragm--regulates the amount of light for viewing the object.
8. Light source--can be electric light, or light reflected from a
mirror.
9. Base--the bottom of the microscope which rests on the lab table.
10. Arm--is a handle which is gripped to carry the microscope.
11. Course adjustment--moves the base to focus the object. The
course adjustment moves the bases a large amount with just a
small twist.
12. Fine adjustment--moves the base to focus the object. The fine
adjustment moves the base a very small amount with each twist.
13. Pillar--part of the arm which meets with the base.
A compound microscope is one that uses two lenses to magnify. One
lens is the ocular. The ocular magnifies the object to 10 times
(10X) its actual size. The other lens in a compound microscope is
the objective.
Most microscopes come with several objective lenses. They have a
low power which magnifies the object 10X, a medium power which
magnifies it 20X, and a high power which magnifies the object 40X
its actual size.
To calculate the total magnification, the power of the objective is
multiplied by the power of the ocular. If the ocular is 10X, and
the objective is 10X, the total magnification is 100X.
The resolution of a microscope is its ability to distinguish detail
in the object. The finest research microscopes are limited to
total magnifications of less than 2,000X, because beyond this
resolution is lost to the point of severe distortion.
If microscope lenses are parfocal, once the object is in focus at
low power, the higher power objectives can be swung into position
and the image brought into focus using only the fine adjustment.
The low power objective can be lowered completely and it will not
touch the slide. However, the higher power objectives can break
the slide and damage the objective if they are lowered completely.
Therefore, you should focus the image under low power, then swung
the higher power objective into place and focus using the fine
adjustment. To focus the object with higher power objectives, you
must lower the objective to about 1/8 inch from the slide while
looking from the side to be sure that the objective does not touch
the slide. It is always easier to focus an object under low power,
and our microscopes are parfocal, so you should never have an
occasion to initially focus the object under high power.
Use and care of the microscope:
1. Always use both hands to carry the microscope. One hand should
be used to grip the arm of the microscope, the other hand should
support the base of the microscope. Never tilt the microscope
because the ocular might fall out of the draw tube.
2. Use only lens paper to clean the ocular and objectives.
Handkerchiefs and tissue will scratch the lens.
3. Always focus upward to avoid damage to the lens and slide.
4. Before returning the microscope to its storage cabinet, remove
the slide, put the low power objective into working position,
clean the microscope, and put on its plastic cover.