Introduction to Microscopy
SUMMARY: This lab is intended to help students review the structure and function of the parts of the microscope. Students will practice using the microscope by observing living aquatic organisms.



The microscope is used in laboratories, hospitals and machinist shops. The unaided human eye is unable to see the world in the detail needed to do many necessary things in our modern lives. We use microscopes to view bacteria, young sea urchins, and cancer cells. We observe crystal formation reactions, bullets in forensic investigations and quality in tool production using the microscope. See Mazia.


Parts of the Microscope

1. Eyepiece

Contains a magnifying lens that focuses the image from the objective into your eye.

2. Course Adjust

For focusing under low magnification

3. Fine Adjust

For focusing under high magnification or low

4. Low Power Objective

For large specimens or overview

5. High Power Objective

For detailed viewing or small specimens

6. Specimen on glass slide

What you want to look at

7. Stage

Supports specimen in correct location to lens

8. Condenser

Focuses the light on specimen

9. Diaphragm (iris or disc)

Regulates amount of light and contrast

10. Light Source

Illuminates the specimen for viewing


A Depression slide can be "made" by using a regular slide and three cover glasses

Preparations Before Work Begins

Before observing cultures in sea water: Sea water is incredibly corrosive to metal parts. Never let objectives come in contact with sea water. If this should occur, rinse with distilled water immediately! Wiping down stage with a cloth/paper towel dampened with distilled water once in awhile is an excellent idea.
  1. Students should have an introductory lesson on the use of the microscope. Make sure they can identify and tell the purpose of each part of the microscope. (In most cases the student has done this in prior laboratory activities and classes.)
  2. Remind students to label materials as they work and to keep their lab stations orderly and clean. [this point will pay off a thousand fold if they adopt this practice now!]
  3. Label eyedroppers, test tubes and slides with what they will contain. In the case of sea urchin gametes, mixing them up will result in fertilized eggs before you are ready for embryos.
  4. ALWAYS start observations on any new slide with the lowest power objective. Always return the microscope to the lowest power objective when done observing anything and before putting away the microscope. The shortest lens is the least likely to be "smashed" against a slide or to be dipped in sea water and is the easiest to use to find a new specimen.


  1. If a depression slide is available, students should add a drop of the suspension from the culture to the well on the slide. Or if you are using the 3 cover glass technique, place the two "bridge" cover slips onto the slide and add the drop between the cover slips.
  2. Add the top cover slip.
  3. Observe and focus on the sample using the lowest power objective. Adjust the light source as needed, often lower light optimizes viewing by increasing contrast. The 4x objective is good for scanning a large number of cells. The 10x is good for general observations.
  4. Use the 40x when you need to see more clearly. As students move to the 40x remind them to:
    1. Focus first at 10x.
    2. Leave the course focus knob in position and shift to the 40x while observing that it does not come in contact with the suspension or the cover slip
    3. Use only the Fine Focus knob with the 40x objective.
  5. On some microscopes you may be able to adjust the diaphragm to be "between" stops simulating a "dark field" condition. The cells will be white against a dark background. This is an excellent way to make observations.
Sea urchin eggs/sperm will look something like this:
Brightfield Darkfield
 Tip: Do go around and look through each microscope. Microscopes can get far out of alignment easily and quickly. Students can end up spending an entire period looking at an air bubble or piece of dust if you do not check up on them. Using a video microscopy setup at the front of the class helps immensely in that it gives the students a starting point for comparison. Check for:

Student Cleanup

Size Under The Microscope - lesson plan and graphic for overhead

Use of the Micro-Video Camera using a video camera on a microscope for demonstrations, research projects, etc. includes sources of equipment.