Microscopes give us a large image of a tiny object. A microscope must gather light from a tiny area of a thin, well-illuminated specimen that is close-by. The objective lens of a microscope is small and spherical. It brings the image of the object into focus at a short distance within the microscope's tube. The image is then magnified by a second lens, called an ocular lens (better known as an eyepiece), as it is brought to your eye.
Some microscopes have clips on the flat stage that hold slides in place. A mirror or illuminator at the bottom of the microscope reflects light rays up to the diaphragm through a hole in the stage. Objective lenses magnify the image which is made even larger when we see it through the eyepiece lenses.

There are two basic types of microscopes - compound and stereo.

Compound (Biological) Microscopes.
Compound microscopes highly magnify thin specimen sections mounted on microscope slides. The objective lens is usually a compound lens, a combination of two lenses made from different kinds of glass. When only one lens is used, distortion often results. This distortion (chromatic aberration) is caused because the colours making up light are not refracted (bent) the same amount when passing through a glass lens. When a compound lens is used, any distortion from the first lens is corrected by the second lens.

Biological Microscopes are usually mono (one eyepiece) however some are binocular (two identical eyepieces.) Certain models also have a trinocular head, ideal for photography.

Magnification is determined by multiplying the objective magnification by the eyepiece magnification. Most advanced student biological microscopes come standard with one 10x eyepiece and various magnification objectives (usually 4, 10, 40 and sometimes 100) to provide magnifications of 40x, 100x, 40x and 1000x.
Magnification of 400x is the minimum needed for studying cells and cell structure.

Example of a Biological Microscope	Example Design of a Biological Microscope
Click for Larger Image	Click for Larger Image

Stereo (Dissection) Microscopes
The human eyes and brain function together to produce what is referred to as stereoscopic vision, which provides three-dimensional images of the objects surrounding us. This is because of the brain's interpretation of the two slightly different images received from each of the retinas. When transmitted to the brain, the images are fused together, but still retain a high degree of depth perception, which is truly remarkable. Stereo microscopes take advantage of this ability to perceive depth by transmitting twin images that are inclined by a small angle (usually between 10 and 12 degrees) to yield a true stereoscopic effect.

Stereo microscopes are low power microscopes ideal for exploring natural wonders like insects, rock crystals, plants, etc, although they can be used to view slides at low power.
Top lighting is the best kind to use, as the light will reflect back up off the opaque surface of the specimen.

Magnification is determined by multiplying the objective magnification by the eyepiece magnification. Most advanced student stereo microscopes come standard with 10x eyepieces and zoom objectives (usually .7 - 4.5) to provide magnifications of 7x - 45x.
Magnification of 20x usually gives the best results.

Example of a Stereo Microscope	Example Design of a Stereo Microscope
Click for Larger Image	Click for Larger Image

Back > (Microscopes)