Information on microscope mirrors and mirror-bars. Illumination of objects using light from mirrors.
Microscope Mirror and Mirror-bar
The proper illumination of an object is an important feature, and although there are numerous accessories for properly accomplishing this, which will be spoken of later on, the mirrors alone are effective agents when properly constructed and applied, particularly when no high magnification is used. The plane mirror is usually used on very low powers, and reflects light in about the same intensity as its source. The concave mirror, however, is intended to concentrate the light so that all the rays which strike its surface are reflected toward its optical axis and come together at some point above it, and the rays from the surface being contained within a comparatively small space, cause an increased intensity, This point is called the focal point, and is usually arranged to coincide with the opening of the stage when parallel rays, such as from the sky, are used. When the source of light comes considerably nearer to the mirror, as for instance from a lamp and the rays are diverging, the focal distance becomes considerably longer, and when very close may be twice as long. Some of the intensity is lost in consequence, as well as the degree of convergence. For this reason mirror-bars are so arranged that the distance of the mirror from the stage may be varied to accommodate the variation in the source of light. While this is of considerable aid, there is not sufficient room for a complete accommodation, with the result that, under certain conditions, the utmost effectiveness of the microscope is not obtained.
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