This is a mount fitting that accessories such as flash units attach to. The accessory shoe is usually at the top of a camera.
Adaptor Ring
This allows you to attach a specific sized filter to a different sized lens. It is also known as a stepping ring.
Advanced Photo System (APS)
This is a camera system that originated in 1996. The system introduced a new size of film and a new way of photofinishing however, only APS cameras could be used with the film.
Ambient Light, Available Light or Existing Light
These terms all mean the available light that is surrounding an object. They mean there is no other added light to it.
Angle of Incidence
When a light source strikes something it is called incident light. When it reflects from the object it is called reflected light. The angle of incidence means the angle that the incident light hits the object. It is measured from a line that is perpendicular to the object.
Angle of View or Field of View
This means the extent of the view taken in by the camera lens. The angle of view is determined by the focal length of the lens, in conjunction with the size of the film. A normal or standard lens has an angle of view that is equal to the diagonal of the film.
Aperture
This is basically a small hole in the camera lens. The light passes through this hole to reach the film. Most apertures are adjustable so you can let in more or less light to the film. The size of the aperture on a camera is expressed as in numbers such as '/8 or '/11. You can set the aperture manually or automatically on most automatic cameras.
Artificial Light
This is essentially any man made form of light, such as flash, lamps and even fire.
ASA
This is the old system of film speed rating. It stands for the American Standards Association. This system has been replaced by the ISO system. A film will show its speed as 100 ISO or 800 ISO, etc.
Aspect Ratio
This is the ratio of something's length to its width. A 35mm film has an aspect ratio of 3:2. Most computer monitors and digital cameras will have an aspect ratio of 4:3.
Auto Exposure
This is often used on automatic digital cameras. The camera will read the exposure meter and will then automatically set the shutter speed and aperture to match the reading. This is to ensure the settings will give too a good photo in the present lighting conditions.
