<P> In addition to an aperture stop, a photographic lens may have one or more field stops, which limit the system's field of view . When the field of view is limited by a field stop in the lens (rather than at the film or sensor) vignetting results; this is only a problem if the resulting field of view is less than was desired . </P> <P> The biological pupil of the eye is its aperture in optics nomenclature; the iris is the diaphragm that serves as the aperture stop . Refraction in the cornea causes the effective aperture (the entrance pupil in optics parlance) to differ slightly from the physical pupil diameter . The entrance pupil is typically about 4 mm in diameter, although it can range from 2 mm (f / 8.3) in a brightly lit place to 8 mm (f / 2.1) in the dark . </P> <P> In astronomy, the diameter of the aperture stop (called the aperture) is a critical parameter in the design of a telescope . Generally, one would want the aperture to be as large as possible, to collect the maximum amount of light from the distant objects being imaged . The size of the aperture is limited, however, in practice by considerations of cost and weight, as well as prevention of aberrations (as mentioned above). </P> <P> Apertures are also used in laser energy control, close aperture z - scan technique, diffractions / patterns, and beam cleaning . Laser applications include spatial filters, Q - switching, high intensity x-ray control . </P>

What is another word for aperture in photography