Optical (also called light) microscopy makes use of a defined light path and linear optics to enlarge the size of tiny objects and produce an image. In this case, tiny means submillimeter size. However, the object should not be smaller than the wavelength of light, as will be shown later. This limitation thus imposes the minimum detectable size attained by this technique, i.e., a few hundreds of nanometers.*
Image formation requires the following events to occur: the object is illuminated and diffracts part of the light; both the diffracted and nondiffracted light are collected by an appropriate lens; and through interference they produce the image at a certain position-the image plane.