The Microscope

-Historical background-Parts and functions of a Compound Microscope

-How are images formed in a Compound Microscope

Roel R. Maraya and Erlina C. Pitac

BEEdBsEd 4-I

Historical Background:

• 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. Biology 2006)

• Is an optical instrument used to observe minute objects through magnification .

(-microscope.org/basic)

Sample Picture of a Microscope

A Laboratory Model of Compound Microscope

The Compound Microscope

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 object.–Some are monocular others are

binocular.

Take note!

Before we use a microscope, it’s important for us to know its parts and their function...

Parts of a Compound Microscope

The Parts and Functions• Eyepiece Lens– the lens at the top that you look through. 

They are usually 10X or 15X power. • Tube –Connects the eyepiece to the objective

lenses• Arm –Supports the tube and connects it to the

base• Base –The bottom of the microscope, used for

support

• Illuminator  –A steady light source or mirror for

light source.

• Stage  –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 slide. 

How are images formed in a Compound Microscope???

Before we answer that. Let’s have first an activity...

Activity 1

• Mechanics: – 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

bond paper.– 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 focusing.

• 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!”

Activity Starts Now!

How are images formed in the microscope?

The ray diagram shows the principle of a compound microscope.

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.

Principle of Compound Microscope

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 lens.

• 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 the object.

References

A. BooksRamos, Gliceria B., Biology Revised Edition, 2006, pp.23-26

B. On-line Sourceshttp://www.microscope-microscope.org/basic/microscope-parts.htmhttp://www.colorado.edu/physics/phys1230…