With powers of magnification that may go up as high as 640xs, they can easily be used to teach medical students. Most compound microscopes have a selection of objectives, often three or four. The usefulness of teaching compound microscopes stretches way up into the medical sciences. A standard eyepiece has a magnification of 10x, and if your objective lenses have magnification power of, for example, 10x and 40x, then you have total magnification powers of 100x and 400x (the total of the eyepiece multiplied by the magnification of each individual objective lens). This is just an example. As you can see, it’s easy to work out the total magnification of any teaching compound microscopes like this.

Teaching compound microscopes are valuable pieces of equipment, so it’s worth looking after them. Remember to turn off all light sources when you’ve finished viewing. Probably the most important instrument for many biologists is the microscope.  The most commonly used is a light microscope.  In order to understand the principles of the Scanning Electron Microscope it is expected that you first gain a basic understanding of the principle and function of standard type light microscopes.  It’s also a good idea to keep your microscope covered when not in use to protect it. Certainly it shouldn’t be exposed to extremes of temperature, and particularly not cold, damp ones. While, it is a delicate and expensive piece of equipment, the light microscope is relatively easy to use and care for compared to many other laboratory instruments.

The purpose of this section is for the student to gain working knowledge of the parts, purpose, and proper use and care of the microscope so that he or she will feel comfortable and competent when using this instrument.  It may be for these reasons that the microscope is often treated so casually and, therefore, abused, resulting in expensive repairs. It also provides a brief description of some of the laboratory techniques used in light microscopy and comparisons will be made for sample preparation and theories of focus, when discussing the Scanning Electron.  A compound microscope is one that uses a combination of lens systems: the objective lens system and the ocular or eyepiece lens system.  The microscope most commonly in use in the microbiology laboratory is the compound microscope.

The objective lenses are the lenses nearest the specimen or object while the ocular or eyepiece lenses are the ones nearest the eye.  Light from the illuminator system passes through a filter (usually a blue filter) and is collected into the sub stage condenser. Other important parts of a compound, bright-field microscope include an illuminator system, a sub stage condenser system, an iris diaphragm, Nicol prisms, a tubular barrel and a mechanical state.  The sub stage condenser then focuses the light on the specimen while the iris diaphragm regulates the amount f light.

Light, as it passes through the specimen, requires an image that is magnified by the objective lens system.  Since the image is optically too close to the eye to be observed clearly, the ocular or eyepiece lens acts as a magnifier to help the eye to focus on the primary image.  The objective lens acts as a small projection lens by forming an enlarged, inverted image of the specimen about 11 mm from the top of the microscope tube; this image is referred to as a primary or aerial image.