Introduction To the Compound Microscope

Microscopes are instruments used to magnify very small objects that cannot be seen with the naked eye. In this lab, you will get familiar with the parts of the microscope and how to use it to view microscopic organisms larger than bacteria. We will observe bacteria in the next lab which will require using an oil immersion lens. In this lab, you will use either a monocular or binocular compound microscope at magnifications 40, 100, and 400 times bigger than the specimen on the slide.

Collecting the Microscope

Make sure that you know where your microscope will be placed before you attempt to transport it. Do you need to clear the desk? Do that first
Collect a microscope from the cabinet (your instructor will show you where this is located)
Carry the microscope to your desk by grasping the arm with your dominant hand and using your other hand to support the base. Never hold the microscope by the stage or lens
When placing down your microscope, make sure that all legs land on the surface at the same time. This makes for a smoother landing and less damage over time

Getting to Know Your Microscope: Parts and Function

You will get to use a microscope similar to the one in the image below or it may look a bit different depending on the make and model. Take time to review the different parts of the microscope and get familiar with the function of each part.

Ocular Lens or Eye Piece: Lens at the top that you look through (usually X10 magnification)

Objective Lens: Used in combination with eyepiece lens to magnify the specimen (usually X4, X10, X40, and X100)

Carrying Handle or Arm: Supports eye piece and base. Grasp this when transporting the microscope

Nose Piece: part of the microscope that holds more than one lens and is capable of rotating to change power

Aperture: The hole in the middle of the stage that allows light through to the slide

Stage with Clips: The part where the slides are mounted. The stage can be moved up and down when focusing the specimen. Clips hold the slides in place

Light Source or Illuminator: Provides the light needed to pass through the slide so that the specimen on the slide can be seen

Coarse Adjustment Knob: Knob used to quickly bring the specimen into focus

Fine adjustment Knob: Knob that slowly, but precisely brings the specimen clearly into focus

Condenser: Focuses the light on the specimen

Condenser Aperture Lever: Adjusts the amount of light hitting the slide through the condenser

Light Intensity Control: Controls the intensity of light coming from the bulb

Parts of microscope. *Source: Wikimedia Commons*

How to View a Specimen (Step by Step)

Plug in the microscope to the power source
Make sure that the X4 (scanning objective) lens in clicked in position to view the specimen (we always start with the lowest objective lens)
Use the coarse adjustment knob to put the stage to its lowest position
Place slide on the stage and clip it in place
Center the specimen over the aperture
Switch on the light source
Use the coarse adjustment knob to move the stage until the specimen comes into focus
Use the fine adjustment knob to make the image sharper
Use your cell phones to take a picture of the image on the slide. Alternatively, draw the image that you see.
To move to a higher magnification, DO NOT MOVE THE STAGE OR SLIDE. Simply rotate the nose piece so that the X10 (low objective) lens is in position. DO NOT MOVE THE COARSE ADJUSTMENT KNOB. Instead, simply adjust the fine adjustment knob to bring the specimen in focus.
Use your cell phones to take a picture of the image on the slide. Alternatively, draw the image that you see.
Follow the same procedure to view the specimen on the X40 (high objective) lens. We will stop here. I will show you how to use the X100 (oil immersion) lens in the next class
Use your cell phones to take a picture of the image on the slide. Alternatively, draw the image that you see.
When you are finished looking at a specimen, lower the stage to its lowest position, remove the slide, and repeat the process with a new specimen

Putting the Microscope Away

Turn off the light
Unplug the electric cord
Make sure that the cabinet door is opened before going over to return it. If not, you will be forced to hold the microscope with one hand. Practice to keep both hands on the microscope
Transport the microscope by grasping the arm with your dominant hand and using your other hand to support the base

Lab Report

Show images or drawings of at least two specimen at each level of magnification on the compound microscope. Make sure to indicate the scientific name of the specimen (30 points)
If the eye piece magnification is X20, how much bigger will the specimen appear if you were looking at it using the X10 and X40 objective lens respectively? (4 points)