Biology 1: Principles and Themes

An Introduction to the Laboratory

Microscopy

The microscope is perhaps the most basic tool used by biologists. Light microscopy was first applied to biological materials in the seventeenth century by such researchers as Robert Hooke and Antoni van Leeuwenhoek. The impact of this invention on the course of human endeavor is easily underestimated. Within a short span of time, that which was invisible to the human eye became visible. Events such as the causes of certain diseases and the decay of food, previously described as spontaneous generation or supernatural could now be explained. An entire world of living organisms previously unknown was now available for study. The microscope remains a pivotal tool in learning biology to this day, with most laboratories being equipped with one or more research instruments.

Over the course of this year, you will be using two different types of microscope:

I - Compound (Light) Microscope

II - Stereoscopic (Dissecting) Microscope

These microscopes are delicate and expensive instruments and must be treated with care.

When using a Compound Microscope please keep the following in mind:

When transporting your microscope always pick it up by the arm. Hold it upright and support the base with your free hand.
The arm supports an inclined body tube, which in turn supports the magnifying elements of the microscope. At the end of the tube is the ocular, one of the magnifying elements. The other magnifying elements are screwed into a revolving nosepiece at the bottom of the body tube; these are called objectives. Together, the ocular and an objective constitute the magnifying system of the microscope. The objective provides for the primary or initial magnification of the object being viewed while the ocular provides the secondary or final magnification and generates the image seen by the viewer.
Underneath the body tube and nosepiece is a flat plate, the stage, upon which objects to be examined are placed. Directly beneath the stage opening you will notice a system of lenses, the condenser, which serves to concentrate the light from the illuminator below.
Light plays an extremely important role in the operation of a compound microscope. The critical importance of light makes necessary its careful adjustment, and several controls are available for this purpose. The iris diaphragm may be found just below the condenser lens system. This control is one of the most important on your instrument.
Just as with a magnifying glass, viewing an object with the microscope requires that the lens be a certain specified distance from the object. That distance is a property of the lens system, and is constant for any particular objective; it is called the working distance. At the working distance from an object, the objective is in focus. Changes and adjustments in the focus, which are necessary when an object is first placed on the microscope and essential in order to perceive depth, are accomplished by means of coarse and fine adjustment knobs usually located on the arm. Note that the fine and coarse focus knobs are separate on some of our microscopes and combined on others.

You should be able to locate the terms in bold on the image of the light microscope above, or click here if you are having problems.

Keep the following in mind when using a Stereoscopic Microscope:

The depth of field is much greater than with the compound microscope, which allows objects to be view in three dimensions
The optics do not invert images
To focus close your left eye and adjust the focus of the image viewed with the right eye. Open your left eye and close your right eye and adjust the focus for the left eye using the secondary focus ring located on the left ocular.
All of our stereo microscopes are binocular. To obtain the correct interpupilary distance for your eyes you must adjust the distance between the two oculars by gently pushing or pulling the oculars until you see the object as a single image.
Note that the dissecting microscope is not parfocal and must be re-focused when the magnification is changed

Consider the following questions for both the light microscope and the stereoscopic microscope

When you move the slide to the right while looking into the microscope, which way does the image appear to move?
Which way does the image move when you move the slide toward you?
Away from you?

Click here to view the letter F slide as seen through a compound light microscope
Click here to view the letter F slide as seen through a stereoscopic microscope