Introduction to Microscopes

PART A - Microscope parts

  1. Collect each microscope pictured and become familiar with the parts marked on the diagrams.

  1. Examine the monocular microscope images above and complete the table. Use the word list below and copy the word into the correct spot:

Eyepiecebody tubehigh and low power objectivesstagecondenser

iris diaphragmmirrorcoarse and fine adjustment knobsbasearm

Part / Name / Function
1 / A platform where the slide is positioned with clips to hold it in place.
2 / Reflects light up through the slide to the eyepiece.
3 / The lens that the operator/person looks through.
4 / This concentrates the rays of light and directs them onto the object being viewed.
5 / A tube that the eyepiece and nosepiece are attached to.
6 / Moves the body tube up or down for focusing; can be coarse or fine.
7 / Lenses used to see the detail of the specimen; can be low power or high power.
8 / Can be adjusted like a camera shutter to control the light passing through the object and the body tube.
9 / Supports and stabilises the microscope.
10 / Holds the body tube and can be used as a handle for holding the microscope when carrying.
  1. Complete this Venn diagram comparing the binocular or stereo microscope to the monocular microscope. Write features common to both microscopes in the middle and in the separate section of the circles if only found on either the monocular or stereo microscope. You can research on the internet to add more information.

Correct procedures for use of a microscope

  1. Check that the eyepiece lens and objective lens are clean by looking down the barrel. Check the mirror is clean. Wipe with lens tissue and alcohol if necessary.
  2. Condensers should be correctly adjusted prior to the lesson. If so instruct students not to touch the condenser knob. If not adjusted, ask students to raise the condenser as high as possible.
  3. Rotate the nosepiece to select the low power lens (X10) suggested when viewing cells.
  4. Adjust the angle of the lamp and mirror so that light is directed up the barrel.
  5. Place the slide on the stage and secure with clips. (If using a wet mount make sure the slide is dry and has a cover slip.)
  6. Adjust the light intensity using the iris diaphragm.
  7. Looking from the side, lower the objective lens until it is just above the slide.
  8. Look through the eyepiece and use the coarse focus knob to move the objective lens up until the object is in focus.
  9. To draw cells or view the specimen under high power (X400), carefully rotate the nosepiece until the X40 lens is in position. The lens will fit if correctly focused under low power. The object should be visible, as most microscopes are parfocal.

Adjust the image using the fine focus knob only. NB: Do not touch the coarse focus knob again, once you have focused under low power.

PART B - Magnification and focusing

Total magnification of a microscope = eyepiece lens x objective lens

magnification magnification

Each lens is labelled with an “X” and then a number, which tells you how much it multiplies.

For example, if the eyepiece lens is 10X and the objective lens is 40X, the total magnification is 400X, meaning the object you are viewing is magnified 400 times larger than normal.

Place a prepared slide onto the stage of the monocular microscope. To focus the microscope, follow the following steps:

1.Turn the nosepiece so the objective lens being used is the lowest magnification

What is the total magnification at low power?

2.Look through the eyepiece and either angle the mirror so the light is bright and evenly lights the field of view, or, make sure the built-in light is switched on. If the light is too bright, adjust the iris diaphragm.

3.Place the prepared slide onto the stage and move the clips over the slide edges to hold it in place.

4.Raise the stage while looking side on at the microscope.

5.Look through the eyepiece and adjust the fine focus knob so that the image comes into focus.

6.Once the slide is in focus and you can clearly see the specimen, you can use a higher objective lens. If you then need to bring the specimen into focus, only use the fine focus knob.

Change to a higher power (medium or high). What is the total magnification now?

  • Look at the various prepared slides provided, practicing focusing on both low and high power. Remember to start with the low power first.
  • Try setting up the focus on a stereo/binocular microscope.

Can you use the prepared slides with this type of microscope?

What sort of things can you examine with this microscope?

PART C - The field of view

Sometimes abbreviated "FOV", the field of view is the diameter of the circle of light that you see when looking into a microscope. As the power gets greater, the field of view gets smaller. You can measure this by placing a clear metric ruler on the stage and counting the millimetres from one side to the other.Typically, you will see about 4mm at 40X, 1.6mm at 100X, 0.4mm at 400X and 0.18mm at 1000X. You see less of the specimen but in more detail as you increase the magnification.

Set up the monocular microscope on its lowest magnification.

  1. Place a thin plastic ruler on the stage and bring it into focus.
  2. Measure the diameter of the field of view in mm and record it in the table, repeating for higher magnifications as well.

Low power / Medium power / High power
Eyepiece lens / x10
Objective lens / x4
Total magnification / x40
Diameter of field of view (mm)

As the magnification ______the field of view ______. (increases/decreases)

PART D - Moving the slide

  1. On a clean microscope slide draw a small letter a, roughly the size of newspaper print, using a non-permanent marker.
  2. As before, set up the monocular microscope on low power and place the slide on the stage with the letter “e” in the usual reading position (meaning not upside-down or sideways).
  3. Look into the eyepiece.

Q. What do you notice about your letter? Is it upside-down? Back-to-front? Can you see all of it? Describe and draw what you see.

  1. Now move the slide to your right.Which way does the letter move? Try moving the slide to the left, then up and down. Which way does the letter move for each new position? Answer in the table below.

Monocular microscope / Binocular microscope
Movement of slide / Movement of letter / Movement of slide / Movement of letter
To the right / To the right
To the left / To the left
Up / Up
Down / Down
  1. Repeat these steps for high power and the binocular microscope. Record your observations on the table above.

PART E - Preparing a wet mount instructions

  1. Place a drop of water on the centre of a clean dry slide using a pipette.
  2. Using the forceps or a pipette, place the specimen in the middle of the drop.
  3. While holding the cover slip upright, carefully place one edge of the cover slip next to the water.
  4. Slowly lower the upper edge of the cover slip onto the water (you can use a compass point or something with a fine point like forceps to help lower the cover slip). The objective is to minimise or eliminate air bubbles under the cover slip.
  5. An absorbent towel can be placed at the edge of the cover slip to draw out some of the water, if necessary, further flattening the wet mount slide. Ensure the microscope does not get water in it, by not tilting it and blotting up any excess water with paper towel.

You will prepare a wet mount of onion cells and you will need to add a dye after step 2.

Why do you need to add a dye as well as water?

PART F - Drawing specimens

  1. Place the prepared slide onto the stage of the monocular microscope.
  2. Put the microscope on low power and focus the image. Now put the microscope on high power and see which is the best view. Draw what you see using the following rules:
  • Learn to keep both eyes open. Use one eye for viewing and one for drawing. This may take some practice!
  • Only draw using lead pencil and blank, unlined paper.
  • Draw the specimen in a circle which represents the field of view ad try to draw the specimen to scale (so it should appear as big when compared to the circle as it does when you look down your field of view).
  • Do not shade or colour the parts, just draw the outline of the image. You only need to draw one or two cells, not all the cells in view.
  • Include the name of the specimen, the date and the total magnification.
  • A stain is often used to highlight parts of a cell that cannot easily be seen. A stain is a dye that colours different parts of the cell to make them more clearly visible. If a stain is used, the stain must also be recorded.
  • Write a description next to the diagram.

Your own specimen drawings:

Onion cells / Prepared slide: ______cells