How to Use a Microscope

Different types of light microscopes and dissecting microscopes are used in the School’s teaching labs. With the compound light microscope you can see things such as cells that are beyond the limits of resolution of the human eye. In order to be successful in your academic pursuits in biology, it is important to gain an appreciation of the microscopic world. Learning how to set up a microscope correctly is critical to achieve this success. In addition to assist you in gaining proficiency in microscopy, this learning module has a component designed to assist you with recording your observations and drawing to scale.

Your microscope is a precision instrument. Please handled it with care; carry it with both hands and once on your bench, lift (avoid dragging) the microscope to where you will be using it.

| set up | adding scale bars | parts of the microscope |

How to set up for the “Motic” Microscope

Make sure to sit comfortably with the microscope directly in front of you. Turn on the microscope at the power switch; adjust the light intensity by turning the dial only about 3-4 mm (not too high so as to avoid eye-fatigue).

1. Focus the slide. Put a slide on the microscope and, using low power (LP, i.e. with the 4X objective in position).  focus the image by looking down the microscope using the focus control knobs (fine and course focus are co-located on either side of the microscope).  At high power (40X and above), only the fine focus controls are used.

2. Focus the condenser using your left hand. To do this, close the field diaphragm over the light source (knurled ring around the light source) so that you can see the edges of the diaphragm when you are looking down the microscope. Adjust the condenser height (LHS condenser knob) so that the edges of the diaphragm become sharp. Expand the field diaphragm so that it extends just outside the field of view. The condenser should be not very far (about 3 mm) from the specimen stage when the condenser is in the correct position. Now, open the field diaphragm to the point where the diaphragm is no longer visible, i.e., just outside the field of view.


3. Adjust for your eyes. Each eye-piece can be focused independently to accommodate differences between your left and right eye. With the focus controls, focus the specimen on the stage with one eye closed, then close that eye and open the other. This time use the eye-piece focus control of the eye that is open to focus the image. Now, with both eyes open, look at the specimen and adjust the distance and angle between the eye-pieces as necessary.  You should now be able to use both eyes to view your slides and by using both eyes you will avoid eye strain.

4. Adjust the condenser sub-stage iris diaphragm to match the objective every time you change magnification. Once the specimen is focused, adjust the condenser iris diaphragm (numbered dial under the specimen stage) so that the numeric aperture matches that of the objective in use. The numeric aperture of each objective is next to the magnification and are as follows: 4 X = 0.10; 10 X = 0.25; 40 X = 0.65; 100 X = 1.25.  This adjustment needs to be made every time you switch between objectives.

5. When you have finished with your microscope make sure it is clean, dry, you have removed any slides from the stage and the 4x objective is in place.  Please leave your microscope in the same condition that you would like to find it. Please check with a demonstrator if you are unsure. 

Step 4 needs to be repeated EVERY time you change objectives (magnification).

Recording your observations and recording scale

In biology any images or drawrings must have a scale so that the observer can interpret it (i.e. relate size of drawing to actual size of section).

Estimating size of the specimen:

There are several ways to estimate size. If you are using the Motic software, and a calibrated system, then the software will allow you to add a scale bar to your image. If not, then you can obtain an estimate of size of the diameter of the field from the table below for the Motic microscopes and then estimate the proportion of the field of view that the specimen occupies.


Or visually:

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Parts of the Microscope

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You can view the explanation of different parts of the microscope in printable format.

Parts of the Motic microscope

© School of Life and Environmental Sciences, The University of Sydney

Contact: Rosanne Quinnell and eResources Unit