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Learn about binocular microscopes.
Binocular Microscopes
The binocular is applicable to almost every kind of microscopical research, but it is not necessary for the student, and I do not recommend those who are beginning to work at microscopical investigation generally to provide themselves with one. The instrument is, however, very desirable for special work, and by its use a more correct idea of many objects may be obtained; but for the ordinary microscopic work undertaken by beginners, and for the examination of vegetable and animal tissues, the usual instrument is to be much preferred. The binocular should be a separate microscope altogether, or it should be possible to remove the binocular tube from the body of the microscope, and substitute for it an ordinary single tube. Binocular for the highest magnifying powers The binocular in ordinary use being suitable only for the examination of objects by powers magnifying less than 200 diameters. The prisms employed are placed above the object-glass. Of the total number of rays which have passed through the object-glass, the greater part are transmitted through the prism and the straight tube of the microscope, but some suffer reflection from its lower surface, and are received upon the reflecting surface of the other Prism in an oblique direction and after emerging from the surface, enter the diagonal tube of the microscope. The two images thus formed are exactly similar, and the two pictures blend and appear to the observer as one, and in relief. There is, however, no true stereoscopic image, for the one picture seems to be in every respect, save in intensity of illumination, the counterpart of the other.
A binocular eye-piece attached to the ordinary single body gives a large field well illuminated, and seems to perform well with low and medium magnifying powers. An adjustable shallow achromatic erector or eye-piece slides in a setting that fits the tube of the single-body microscope. By this an image is formed at the eye-glass end. This image then passes through the flat surface of an equilateral prism placed over the eye-lens, and by it is bisected, one half being refracted towards the right, the other half to the left. After these rays emerge from the prism, they pass into prisms. The rays are lastly transmitted through two deep eye-pieces or oculars superposed over the two prisms. By a small pinion the prisms are adjusted for the variable distance between the eyes of different observers. Improved and simplified that adjustment by the use of a circular disc with two eccentric slots, which entirely supersedes the rack and pinion. The shallow eye-piece, or erector, is made to slide in the eye-piece tube for the purpose of varying the distance between the eye-lens and the prism placed over it, according to the power of the objective in use..
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