-Parts and functions of a Compound Microscope
-How are images formed in a Compound Microscope
Roel R. Maraya and Erlina C. Pitac
• In about 1597 two Dutch eyeglass makers,
Zacharias Janssen and his son Hans were
experimenting with lenses in a tube.
• They observed that nearby objects viewed
through two lenses in line were magnified.
• Their device was the First compound
microscope however its magnification obtained
was only about 10X.
• Galileo also designed a microscope but it
was not usable.
• Robert Hooke the first useable British
compound microscope in about 1655.
• Antoine Van Leeuwenhoek he worked
with lenses and was able to build a good
and usable compound microscope.
What is a Microscope?
• Is an instrument for observation which enlarges
or magnifies and brings into finer details the
visual image of very tiny objects. (Revised Ed.
• Is an optical instrument used to observe minute
objects through magnification .
Sample Picture of a Microscope
A Laboratory Model of Compound Microscope
The Compound Microscope
– has two systems of lenses for greater
magnification, 1) the ocular, or eyepiece
lens that one looks into and 2) the
objective lens, or the lens closest to the
– Some are monocular others are
Before we use a microscope, it’s
important for us to know its parts and their
The Parts and Functions
• Eyepiece Lens
– the lens at the top that you look through. They are
usually 10X or 15X power.
– Connects the eyepiece to the objective lenses
– Supports the tube and connects it to the base
– The bottom of the microscope, used for support
– A steady light source or mirror for light source.
– The flat platform where you place your slides.
• Revolving Nosepiece or Turret
– This is the part that holds two or more objective
lenses and can be rotated to easily change power.
• Objective Lenses
– There are 2 or 3 objectives on a microscope. They
are the 10X, 40X and 100X powers.
• Rack Stop
– This is an adjustment that determines how close
the objective lens can get to the slide.
• Condenser Lens
– The purpose of the condenser lens is to focus the
light onto the specimen.
• Diaphragm or Iris
– This is used to vary the intensity and size of the
cone of light that is projected upward into the
How are images formed in a
Before we answer that.
Let’s have first an
– The class will be grouped into three (3).
– Each group will be given a compound microscope
and a prepared slide.
– They will locate and view the image using the
objectives of the microscope.
– They are to sketch the image viewed on a short
– The activity is good only for 15 minutes.
Ooops! Take note of the Proper
ways of using the microscope...
Click to view the Proper Use
of the Microscope
Proper Use of the Microscope
• When moving your microscope, always carry it
with both hands (Figure 1). Grasp the arm with
one hand and place the other hand under the
base for support.
• Turn the revolving nosepiece so that the lowest
power objective lens is "clicked" into position.
• Place the microscope slide on the stage and
fasten it with the stage clips. You can push down
on the back end of the stage clip to open it.
• Using the coarse adjustment, lower the
objective lens down as far as it will go without
touching the slide!
• Look through the eyepiece and adjust the
illuminator (or mirror) and diaphragm.
• Slowly turn the coarse adjustment so that the
objective lens goes up (away from the slide).
Continue until the image comes into focus.
Use the fine adjustment, if available, for fine
• Move the microscope slide around so that the image is
in the center of the field of view and readjust the
mirror, illuminator or diaphragm for the clearest image.
• You should be able to change to the next objective
lenses with only slight focusing adjustment. Use the
fine adjustment, if available. If you cannot focus on
your specimen, repeat steps 4 through 7 with the
higher power objective lens in place. DO NOT ALLOW
THE LENS TO TOUCH THE SLIDE!
• The proper way to use a monocular microscope is to
look through the eyepiece with one eye and keep the
other eye open (this helps avoid eye strain). If you have
to close one eye when looking into the microscope, it's
ok. Remember, everything is upside down and
backwards. When you move the slide to the right, the
image goes to the left!
• Do not touch the glass part of the lenses with
your fingers. Use only special lens paper to
clean the lenses.
• When finished, raise the tube, click the low
power lens into position and remove the slide.
“Remember, microscopes are expensive scientific
instruments. Handle them properly and
carefully and they will last for many years!”
How are images formed in the microscope?
The ray diagram shows the
principle of a compound
The object is mounted on
the stand below the microscope
tube. The objective lens forms a
real, inverted and magnified image
(I1) of the object. The image I1 acts
as an object for the eye piece. The
position of the eyepiece is so
adjusted that the image lies within
the focus of the eyepiece (Fe). The
eyepiece acts like a magnifying
glass and forms a virtual erect and
magnified image of the object. Click the image to enlarge.
Image Formation in a Compound Microscope
• The object (O) is placed just
outside Fo, the principal focus of
the objective lens.
• Fe is the principal focus of the eye
• A real, inverted magnified image I1
is formed. The magnified image I1
acts as an object for the eye lens.
• The final image I2 is virtual and is
magnified still further. It is
inverted compared with the object.
I2 may appear 1000 times larger than
Ramos, Gliceria B., Biology Revised Edition, 2006,
B. On-line Sources