What is "confocal microscopy"

n. An imaging technique in which pinholes are used to eliminate out-of-focus light

Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of adding a spatial pinhole placed at the confocal plane of the lens to eliminate out-of-focus light. It enables the reconstruction of three-dimensional structures from the obtained images by collecting sets of images at different depths (a process known as optical sectioning) within a thick object. This technique has gained popularity in the scientific and industrial communities and typical applications are in life sciences, semiconductor inspection and materials science.

A conventional microscope "sees" as far into the specimen as the light can penetrate, while a confocal microscope only "sees" images one depth level at a time. In effect, the CLSM achieves a controlled and highly limited depth of focus.