aperture
- In optical waveguide technology, the aperture is the absorption capacity of the light coupling into the front surface of an optical waveguide. In lens coupling, the aperture corresponds to the aperture width of the lens. Rays entering an optical waveguide from a light source are transmitted in the optical waveguide only if the angle of incidence is below the angle of acceptance. Rays that have an angle of incidence greater than this are refracted to the cladding glass and are therefore not available for transmission. The aperture angle is the angle at which the useful edge rays are still transmitted. The sine of this angle is the numerical aperture. If fibers with different numerical apertures are joined together in an optical fiber transmission link, then the feeding fiber should have a smaller or the same aperture and the same or a smaller core diameter as the optical fiber into which the light beam is fed. If the aperture is larger or the core diameter of the feeding fiber is larger, some of the light energy is lost. This is referred to as overfilled launch( OFL), and in the opposite case as underfilled launch (UFL).
- In display technology, the aperture is the ratio of the light-transmitting area to the total area. The values are around 50 % and can be increased to over 80 % by special techniques, such as SHA technology, Super High Aperture (SHA), which works with downsized liquid crystals.
- In video cameras and digital cameras, the aperture is the lens opening. Its aperture determines how much light passes through the lens onto the image sensor. The larger the aperture diameter of the lens, the more light reaches the light-sensitive image sensor. The aperture is specified as a dimensionless f-number ( f-value), which is calculated from the ratio of the focal length to the opening width. A larger f-value, for example f16 or f22, corresponds to a less open aperture, while a smaller f-value, for example f1.4 or f2.8, means that the aperture is wider open. The f-number affects the depth of field and can be included as an artistic element in photography. A small aperture causes a large depth of field.