An aperture, typically rectangular in shape, whose length is large compared to its width. Apertures, generally small compared to the light source, may have fixed or adjustable shapes through which radiation enters or exits an instrument.
SPHERICAL VS. ASPHERIC LENSES
HOW THEY’RE USED IN IMAGING APPLICATIONS
Optical Lenses are often categorized by their shape. Two common surface shapes are spherical and aspherical. Each offers unique characteristics that make it suitable for different use cases.