Compound microscope

1. Use and Care of a
Compound Light
Microscope
Animal and Food Science Department
Brigham Young University Idaho

2. Introduction:
A microscope is a tool that allows us to view things
that are to small to see with the naked eye. The most
common microscope is the compound light
microscope.
It uses a system of two or more lens to collect and
focus the transmitted visible light through the
specimen to the eye. Often this is referred to as
bright field microscopy. Animal cells, plant cells,
bacteria and protozoa can be easily seen using this
type of microscope.

3. A typical compound light microscope is able to
magnify from 40x to 1000x, increasing the ability to
see small details in the specimen. Most microscopes
will have three to four objectives with differing
magnification. They generally have a scanning, low,
high, and oil immersion objectives. Each objective
will be marked with it magnification.

4. The ocular lens also magnifies at generally a 10x
magnification. The power of magnification will be
marked on the lens. It may be monocular or binocular
(one lens for one eye or two for both eyes). The
majority of our scopes are binocular.

5. Total Magnification
Total magnification is the ocular magnification
multiplied by the objective magnification as shown in
the following table.
Objective Magnification Ocular Lens Total Magnification
Scanning 4x 10x 40x
Low Power 10x 10x 100x
High Power 40x 10x 400x
Oil Immersion 100x 10x 1000x

6. Anatomy of a compound light
microscope

7. Set up and Use
1. Remove the dust cover. Carry your microscope
with two hands, one under the base and the
other gripping the arm or frame to the
appropriate bench.

8. 2. Gently place the microscope on a flat, level
surface and plug the microscope into a power
outlet.
3. Turn on the light source The on button may
appear on the back or side of the microscope.

9. 4. Adjust the brightness of the light source. A low
setting is generally best for scanning a slide. This is
done by one of two ways depending on the
microscope that you are using.
One way to adjust brightness is to adjust it using the
brightness adjustment located on the side of the
microscope.

10. This model generally also has an adjustable
condenser. It is generally marked for the individual
objectives. Set the condenser accordingly.

11. On older microscopes the brightness is adjusted by
turning the Illumination Ring on top of the light source.
By turning the ring you can decrease the amount of
light or increase the amount of light being shown
through the sample

12. 5. Adjust the stage as low as possible with
the coarse focus knob. It is the outer or
larger knob.
6. Rotate the nose of the microscope so that
the lowest objective is in line with the light
source.

13. 7. Place a slide on the stage holding it with the slide
clip. If a slide has a coverslip –it should always face
up.

14. 8. Once your slide is correctly seated, look through
the ocular lens, adjust your brightness and using the
coarse adjustment knob (outer knob) bring the stage
up towards the objective, stopping when the slide
image comes into view. The slide should never be
pushed all the way up to the objective.

15. 9. Once the image if seen use the fine focus
adjustment knob (inner knob) to sharpen in on the
details of the structure. After this point you will only
use the fine focus on the slide. All coarse adjustments
have been made.

16. With the scanning or lowest objective in use- you
may scan across the slide by moving the stage from
right to left and left to right. This is done using the
stage knobs found just below the stage of the
microscope.

17. As you scan across the slide you may need to use the
fine focus (inner knob) to sharpen the image. Once
you decide on an area of the slide you may want to
look at a higher magnification of the area.
This is done by rotating the nose of the microscope to
the next objective. On our microscopes that is a 10X
objective. Once the object has been rotated and
locked into place and you have made your light
adjustments (generally brighter); look through the
eyepiece and using only the fine adjustment knob
sharpen the image.

18. If the magnification still does not give the detail that
you need the nose of the microscope may be rotated
again to lock in the third objective which in our case
is a 40X. Again brightness may need adjusted and the
fine focus is used to focus and sharpen the image.

19. To view significantly small structures the oil
immersion objective (100x) may need to be used.
This is used by rotating the nose of the microscope to
between the third objective and the oil immersion
objective. At this point a small drop of oil is placed on
the slide and then the oil immersion objective is
rotated in passing through the oil on the slide.

20. Immersion oil should only be used with the oil
immersion objective. Once oil is used the slide must
be properly cleaned prior to viewing it with any of
the other objectives on the microscope. An increase
in light will be needed and only the fine focus
adjustment should be used to focus the image.
DO NOT under any circumstance use the coarse
adjustment as you will crush the slide into the
objective and potentially damage the objective and
the slide.

21. If you get oil on the other objectives notify the laboratory
manager as soon as possible so that the objectives can be
removed and properly cleaned. If the oil is allowed to dry
on the objective it will not come off and all images
viewed thereafter will have a haze and not focus
correctly.
10. When finished viewing your image- use the coarse
adjustment knob to lower (go away from) the objectives
of the microscope. Rotate the nose of the microscope to
the scanning or 4x objective. If oil has been used, use lens
tissue and cleaner to remove the oil from the slide,
objective, and stage.
11. Turn off the light and unplug the microscope. Cover
the microscope with a dust cover.
12. Return the microscope to the shelf.
13. If you encounter any issues tell or ask your lab
assistant, instructor or laboratory manager.