Cover slip

A cover glass is about 100 to 200 microns -thin, square (often 18 mm x 18 mm), rectangular or circular glass plates. It is used in light microscopy for covering preparations. For aqueous preparations it may delay dehydration. It is important that a smooth optical surface is formed to pass through the light beams without unpredictable deflection. With the use of immersion oil in high-resolution microscopy prevents mixing of the immersion oil with the preparation.

Many microscopic preparations are themselves (often in a surrounding medium such as water or glycerol) constructed from a one millimeter thick slide, the object to be observed and a cover glass, which covers the object. The term " cover glass " but has so far spun off that glass plates of similar thickness are also referred to as if they are not used for covering, for example, when cells are grown directly on coverslips to them in an appropriate cell culture chamber from below with a microscope reverse design ( inverted microscope ) to watch.

The coverslip is part of the optical imaging path, and must be taken into account in the design of the lens. With lenses that have been calculated for use with glass cover, so the image quality suffers when they are used without cover glass (and vice versa). However, up to a numerical aperture of 0.30 lenses can usually be used without cover glass both with; Lenses for oil immersion, even up to a numerical aperture of 1.25. With larger numerical apertures produce a wrong thickness or refractive index of the cover glass aberrations, especially spherical aberration. Lenses are therefore internationally standardized on coverslips of thickness 0.17 mm and the refractive index of ne = 1.5255. Must be used, however, are also coverslips other thicknesses widespread, allowing for high-resolution microscopy either the right cover glass during sample preparation or a lens with a cover slip thickness correction ring (eg, C -Apochromat 40x / 1.2 W Korr for cover glass thicknesses between 0 14 mm and 0.18 mm).