The compound microscope which is most commonly used today contains several lenses that magnify the image of a specimen under study. The total magnification of the object is a product of the magnification of the individual lenses; if the objective lens magnifies 100 -fold (a 100x lens, usually employed) and the eye piece magnifies 10- fold, the final magnification recorded by the human eye or on film will be 1000- fold (100 x 10).
The limit of resolution of a light microscope using visible light is about 0.2µm (200nm). No matter how many times the image is magnified, the microscope can never resolve objects that are less than ≈ 0.2µm apart or reveal details smaller than ≈ 0.2 µm in size Samples for light microscopy are usually fixed, sectioned and stained. Specimens for light microscopy are usually fixed with a solution combining alcohol or formaldehyde, compounds that denature most protein and nucleic acids.
Usually the sample is then embedded in paraffin or plastic and cut into thin sections of one of a few micrometers thick using a microtome. Then these sections are stained using appropriate stains.
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