A typical bacterial cell is about 1 u m while a virus is more in the range of 10-100 nm. Remember, Leeuwenhoek was probably the 1 st to see microorganisms in the 1600's with his invention of his simple microscopes. Refraction is the bending of light as it passes from one medium to another of different density. Immersion oil, which has the same index of refraction as glass, is used to replace air and to prevent refraction at a glass-air interface. The total magnification of a light microscope is calculated by multiplying the magnifying power of the objective lens by the magnifying power of the ocular lens.
Increased magnification is of no value unless good resolution can also be maintained.
1000X total Most microscopes are designed so that when the microscopist increases or decreases the magnification by changing from one objective lens to another, the specimen will remain very nearly in focus. Techniques of Light Microscopy A. Preparation of specimens Wet mounts are used to view living organisms. The hanging drop technique is a special type of wet mount, often used to determine whether organisms are motile. Smears of appropriate thickness are allowed to air-dry completely and are then passed through an open flame. This process, called heat fixation, kills the organisms, causing them to adhere to the slide and more readily accept stains.