The compound microscope, invented by Zacharias Janssen in 1590, uses convex lenses to magnify microorganisms, cells, and tissues. It consists of objective and ocular lenses, a rotating nosepiece, and an adjustable stage with a light source. The magnification is determined by multiplying the eyepiece and objective lens magnifications. The image is inverted by the objective lenses and then magnified by the ocular lenses to produce a vertical image for observation.
A compound microscope is a microscope equipped with two or more convex lenses. The high magnification produced by these lenses together allows for a detailed study of microorganisms, cells and tissues. These types of microscopes are therefore widely used in scientific and medical research.
Zacharias Janssen, a Dutch eyeglass maker, invented the compound microscope in 1590. Galileo presented his version in 1610. Several other scientists and inventors later helped perfect its design and working capabilities.
The basic design of a compound light microscope consists of convex lenses mounted on both ends of a hollow tube. This tube is mounted on an adjustable rotating nosepiece. There is an adjustable side table under the nose pad; specimen slides are placed or mounted on this stage for observation through the lenses. The stage has a window or hole through which a light source can illuminate the specimen under observation.
The light source can be a mirror reflecting natural light or a lamp in the base. The illuminating beam passes through the stage window and through the sample. The light illuminates the area around the specimen, making the specimen stand out in contrast. The level of contrast is controlled by controlling the amount of lighting. A brighter or dimmer effect is achieved by opening or closing an iris diaphragm below the stage, or by adjusting the height of the lamp.
The upper lenses of the compound microscope, those closest to the observer’s eye, are the ocular lenses or eyepiece. Monocular microscopes have one eyepiece and binocular microscopes have double eyepieces. The trinocular versions have a dual eyepiece and camera mounting arrangement.
The objective lenses are the inferior lenses closest to the object being observed. There may be three or four different ones positioned on the rotating nosepiece of a compound microscope. The nosepiece is rotated to select objective lenses that offer the most suitable magnification for a particular specimen.
The four objective lenses are scan power objective, low power objective, high dry objective and oil immersion objective. They have magnifications of 4X, 10X, 40X and 100X respectively. Ocular lenses usually have a magnification of 10X.
To get the total magnification factor, the eyepiece magnification is multiplied by the objective magnification. So with 10X eyepieces and 100X objectives, you get 1000X magnification. This means that a displayed object is magnified 1000 times its actual size. Higher magnifications are also possible.
When an object is in focus, the objective lenses form a real, inverted image of the object at a point within the primary focus of the ocular lenses. The eye lenses then treat this inverted image as the object and produce a vertical image of it. This image is the magnified one as seen by the observer.
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