Microscope

A microscope produces an enlarged representation of a small object. An optical microscope forms its image using light and an objective; an electron microscope uses an electron beam and different focusing and detection methods. The useful result depends on image contrast and optical resolution, as well as magnification.

For a compound optical microscope, the objective forms an enlarged intermediate image and an eyepiece can magnify that image further. Increasing this second magnification alone does not reveal finer detail than the objective has transmitted. The objective's numerical aperture and the illumination wavelength constrain diffraction-limited detail, while specimen preparation determines which structures create image contrast. A practical check compares the visibility of two nearby features, rather than judging only their apparent size.^[ref]

A microscope slide is a support, usually a flat glass plate, that holds a specimen for an optical microscope. A thin specimen and a cover glass can provide a reproducible optical path through the sample; the appropriate preparation depends on whether the observation uses transmitted or reflected light.

Preparation affects the inference. A thick or uneven specimen can superpose structures at different depths, while compression or drying can change the object being observed. Magnification alone therefore does not establish that an apparent boundary corresponds to a structure in the original specimen.