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Plain or frosted, polished edges or ground edges, beveled corners or not and prepared or blank. Microscope slides are the essential required accessory that you must have in order to use a compound biological microscope. Slides are typically made of soda lime glass or borosilicate glass but the trait that they share in common is that a good quality slide will be optically "flat". What this means is that the thickness will not vary across the width and breadth of the slide so that it will be visually detected. The so-called standard slide is 75 mm x 25 mm and nominally 1 mm thick. These dimensions will be maintained within a micron or two and will never cause any distortion in the image of the sample or cause the microscope objectives to lose parfocality. High quality prepared slides will also adhere to these same dimensions. There are specialty slides such as those used in geology and petrography, but the issues remain the same in terms of getting quality samples. The only time flatness is not an issue is when the various forms of depression slides are used to make suspension preparations.

There are many techniques that are used to enhance images in a compound biological microscope. One of the most common as well as one of the most useful is phase contrast. This technique was developed by Frits Zernike (a Danish physicist) in the 1930's and he was awarded the Nobel Prize in physics in 1953 for this significant contribution to the field of optics. As light passes through a medium of varying density, a phase shift or contrast change occurs as a result of the retardation or slowing of the illuminating wave front. Z ernike developed a method to take advantage of this change. It allows one to view cells in liquid suspension without the addition of stains or other chemical additives that might alter the nature of the sample. The image may be further enhanced with the addition of a green filter since this is the color to which the human eye is most sensitive. This remarkable change in contrast is easily appreciated in the included illustration of two epithelial cells. A microscope equipped with phase contrast allows sample viewing in both brightfield and phase without any additional specimen preparation. Common applications of the phase contrast technique include the examination of spinal fluid, urine, naturally occurring water sources and any other solution in which suspended particulate matter is suspected or needs to be evaluated..