What is the size of the opening in the lens when a picture is taken called?

In optics, an aperture is an opening through which light travels. The aperture and localized focal length of an optical system determine the angle of a batch of rays that come to a focal point in the image plane.

Ray bundles are also referred to as pencils of light. In photography, aperture speaks to the size of the diameter of the aperture stop rather than the physical stop or the opening itself. The aperture stop of a camera lens can be fine-tuned to control the amount of light reaching the film or image sensor.

Aperture-when you hit the shutter release button of your camera a hole opens up that allows your cameras image sensor to catch a glimpse of the scene youre wanting to capture. the aperture that you set impacts the size of that hole. the larger the hole the more light that gets in the smaller the hole the less light.aperture is measured in f-stops, for example f/2.8, f/4, f/5.6,f/8,f/22 etc. moving from one f-stop to the next doubles or halves the size of the amount of opening in your lens (and the amount of light getting through). keep in mind that a change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also this means if you increase one and decrease the other you let the same amount of light in very handy to keep in mind).one thing that causes a lot of new photographers confusion is that large apertures (where lots of light gets through) are given f/stop smaller numbers and smaller apertures (where less light gets through) have larger f-stop numbers. so f/2.8 is in fact a much larger aperture than f/22. it seems the wrong way around when you first hear it but youll get the hang of it.