Aperture signs

APERTURE 

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The small aperture lets in more light which means that when you take a picture it will be really bright but on the other hand if you use a hight number of aperture it will let in a lot of light

picture with less light f18                                           picture with more light f4

this is the difference between the small depth of field and large depth of field