Microscopes A short course

Background Information There is certain terminology used when discussing microscopes. Magnification refers to the ratio of the size seen in the microscope to the actual size of the specimen. On a compound microscope it is usually between 4x and 400x. It is calculated by multiplying the objective times the eyepiece.

Resolution is the clarity and detail seen. It is the minimal distance between two points in which they can be seen separately (i.e.: not blurred). Field of view refers to how much you actually see when looking in a microscope. As your magnification increases, field of view decreases.

Depth of field is the number of layers you see. As you look through the scope, you will notice that you can focus on the top, middle, and bottom of many specimens!

Types of scopes There are four main types of microscopes that a biologist uses: dissection, compound, scanning electron, and transmission electron. DISSECTION, A dissection microscope is light illuminated. The image that appears is three dimensional. It is used for dissection to get a better look at larger specimens. You cannot see individual cells because it has a low magnification. Resolution is low at 120 nm. compound,

Dissection scope photo This is a picture of hair grafts.

Compound microscope A compound microscope is also light illuminated. The image seen with this type of microscope is two dimensional. This microscope is the most commonly used. You can view individual cells, even living ones. It has high magnification (from 4x - 400x). However, it has a low resolution (200nm).

Compound microscope photo These are pictures of diatoms at about 400X.

Scanning electron microscope SEMs use electron illumination. The image is seen in three dimensions. It has high magnification and high resolution (10nm). The specimen is coated in gold and the electrons bounce off to give you an exterior view of the specimen. The pictures are in black and white.

SEM photo This is a mold spore.

Transmission Electron Microscope TEM is also electron illuminated. This gives a two dimensional view. Thin slices of specimen are obtained. The electron beams pass through this. It has high magnification and high resolution(0.2nm).

TEM photo This is a neutrophil, a kind of white blood cell.

Using the Microscope There are a few rules to using the scope. ALWAYS CARRY IT WITH 2 HANDS. 1.First you must plug it in and turn it on. Set it several inches away from the edge of the table! 2. Make sure it is set on the lowest power. 3. Move the stage to the top position. 4. Place the slide on the stage under the clips. 5. Use the coarse adjustment to get the image in focus. 6. Use the fine adjustment to see more detail. 7. Finally move the lens clockwise to move to higher magnification

Parts of the Compound Microscope