The chromatic reflector has the property of reflecting short wavelength light and transmitting longer wavelength light. The point is a diffraction limited spot on the specimen and is produced either by imaging an illuminated aperture situated in a conjugate focal plane to the specimen or, more usually, by focusing a parallel laser beam. With only a single point illuminated, the illumination intensity rapidly falls off above and below the plane of focus as the beam converges and diverges, thus reducing excitation of fluorescence for interfering objects situated out of the focal plane being examined.
Light passing through the image pinhole is detected by a photodetector.
Usually a computer is used to control the sequential scanning of the sample and to assemble the image for display onto a video monitor. Most confocal microscopes are implemented as imaging systems that couple to a conventional microscope. There are some biological applications of this mode of operation such as for detecting gold particles used in immuno-gold labeling. However, in the vast majority of biomedical applications they are used for fluorescence imaging. The improvement can vary between marginal, in the case of very flat specimens like chromosome squashes, to spectacular, in the case of large, whole-mount specimens such as embryos.