Projection Microscope (Marschal A. Fazio)

Author

Marschal A. Fazio teaches at University High School (West Los Angeles)

Principles

A light microscope uses physical properties of light to magnify objects that are too small to see with the naked eye. A microscope can do this through a series of lenses that refract (bend) light we can magnify objects. Unfortunately the resolution of a light microscope is limited by the lens and the wavelengths of electromagnetic radiation we can pick up with our eye (visible light).

Standards

PS3.A: Definitions of Energy

Electromagnetic radiation is a major source of energy on earth

PS4: Waves and Their Applications in Technologies for Information Transfer

Waves are a repeating pattern of motion that transfers energy from place to place without overall displacement of matter. Light and sound are wavelike phenomena. By understanding wave properties and the interactions of electromagnetic radia- tion with matter, scientists and engineers can design systems for transferring infor- mation across long distances, storing information, and investigating nature on many scales—some of them far beyond direct human perception.

Materials needed

Microscope Slides (prepared of student/teacher made) and a power source

Procedure

Although the linked document is for a different model of scope the instructions are basically the same. First you need to open the projector door and pull out the scope. Plug in the power to a power source. Follow the PDF instructions. You can use the scope as a direct projector, as a table top projection device, or use the mirror projections. Each of these ways to use the scope can be used for different tasks.

Explanation

The optical microscope, often referred to as the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples.

From Wikipedia:The optical components of a modern microscope are very complex and for a microscope to work well, the whole optical path has to be very accurately set up and controlled. Despite this, the basic operating principles of a microscope are quite simple.

The objective lens is, at its simplest, a very high powered magnifying glass i.e. a lens with a very short focal length. This is brought very close to the specimen being examined so that the light from the specimen comes to a focus about 160 mm inside the microscope tube. This creates an enlarged image of the subject. This image is inverted and can be seen by removing the eyepiece and placing a piece of tracing paper over the end of the tube. By carefully focusing a brightly lit specimen, a highly enlarged image can be seen. It is this real image that is viewed by the eyepiece lens that provides further enlargement.

In most microscopes, the eyepiece is a compound lens, with one component lens near the front and one near the back of the eyepiece tube. This forms an air-separated couplet. In many designs, the virtual image comes to a focus between the two lenses of the eyepiece, the first lens bringing the real image to a focus and the second lens enabling the eye to focus on the virtual image.

In all microscopes the image is intended to be viewed with the eyes focused at infinity. Headaches and tired eyes after using a microscope are usually signs that the eye is being forced to focus at a close distance rather than at infinity. Which is why a projector scope is often great to use to observe cells for a long period of time, you do not have to worry as much about eye fatigue.

Resolution is probably one of the most important aspects of a good microscope, without the ability to resolve the image, regardless of the magnification available the image will look blurry and poor. Most modern light microscopes have a resolution of about 200nm.

Questions

Explain refraction and reflection?
What is the importance of resolving power in a microscope? What are some limitations to the resolving power of the light microscope?
Draw a diagram of the light source, shining light trough a lens and into the eyes of a student.
What happens to the light as it passes through a convex lens? A concave lens?

Everyday examples of the principles illustrated

Glasses to help us see better. Camera optics.

Photos

Movies

Examples of cells undergoing mitosis under a contrast microscope

References

Microscope master- information on how microscopes work
New York Microscope Co.- Source for microscope parts, vintage an also new microscopes.
physics of optics- An explanation of infinity focus

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