define Aperture answer for 1 marks .. with diagram pls

Dear student,
Aperture is the effect area of a lens or mirror where the refraction or reflection takes place. Aperture controls the marginal rays and thus reduces aberration (irregularities) of the image.
In optics, we mainly talk about two types of aperture; 1. Linear aperture and 2. angular aperture.

Linear aperture is the diameter of the part of the optical system that is exposed to light. Depending upon the optical system the size of the aperture may be fixed or variable.

The angular aperture of an optical system, is defined as the apparent angle of the lens aperture as seen from the focal point.

Regards,