Modernern cameras use a shutter system. Although it is possible to make a camera with a pin hole. But either way there needs to be a mechanism to stop the light from hitting the light sensitive paper which would be a shutter.
Shutter
opening that lets light in
The pupil lets light into the eye.
F22 - All the lenses I have for my 35mm camera have an F22 setting, this lets the least amount of light through the lens.
aperture
The Shutter.
When you click the camera the shutter behind the lens of the camera opens briefly and lets in the light on to the film. I am no specialist and this is what I learnt in school.
The functional opening is the aperture, the opening that controls the amount of light that hits the photosensitive surface. You may have a camera with interchangeable lenses that screw into and out of the camera's body. The opening into which the lens is screwed is not the aperture.
Aperture on a camera is the size of the opening/hole in the lens that allows light through. A larger opening lets more light through per second than a smaller one. The size of the opening also affects the depth of field (DOF) in the photograph in the following way: Large opening ------- Small opening Shallow DOF ------- Deep DOF See these links for more detailed info. Aperture http://en.wikipedia.org/wiki/Aperture Depth of field http://en.wikipedia.org/wiki/Depth_of_field
iris
The largest camera aperture is f stop 1.4, which lets the most amount of light into the camera.
Answer 1A very brief and very over-simplified description is that a camera is: 1. a "box"2. with a light sensitive media [film or electronic light sensing grid] at the back side,3. with an opening [lens or pin hole] at the front to admit light from a subject and to form an image on the media,4. and a method [a diaphragm to control the intensity of the light, and a shutter to control the length of time the light is allow to strike the media] of controlling the amount of light getting to the media.
A simple camera can be made simply with a light-tight box and a film or sensor, anything to 'capture' the light coming through an opening (lens, pinhole, aperture, etc.) Although this setup is rather rudimentary, it is a camera.