In the confocal microscope all structures out of focus are suppressed at image formation.
This is obtained by an arrangement of diaphragms which, at optically conjugated points of the path of rays, act as a point light source and as a point detector respectively.
Rays from out-of-focus are suppressed by the detection pinhole.
The depth of the focal plane is, besides the wavelength of light, determined in particular by the numerical aperture of the objective used and the diameter of the diaphragm.
At a wider detection pinhole the confocal effect can be reduced.
To obtain a full image, the image point is moved across the specimen by mirror scanners.
The emitted/reflected light passing through the detector pinhole is transformed into electrical signals by a photomultiplier and displayed on a computer monitor screen.
Major improvements offered by a confocal microscope over the performance of a conventional microscope may be summarized as follows: