The document defines key photography terms such as exposure, video gain, iris, f-stop, focal length, and depth of field. Exposure refers to the total amount of light entering the lens, while video gain boosts picture brightness. An iris is an adjustable lens opening that controls light levels, and the f-stop indicates the iris opening size, with larger numbers meaning a smaller aperture. Focal length is the distance from the lens to the camera's sensor for a focused image at infinity, and depth of field is the range of distances that appear in focus, depending on focal length, f-stop, and object distance.

1. Exposure
 Exposure refers to the total amount of
light allowed to enter the lens.

2. Video Gain
 Video gain is the electronic amplification
of the video signal, boosting primarily
picture brightness.

3. Iris
 An iris is an adjustable lens-opening
that controls the amount of light
passing through the lens.

4. f-stop
 The f-stop is the calibration on the lens
indicating the aperture, or iris opening,
and therefore the amount of light
transmitted through the lens.
 The larger the f-stop number, the smaller the
aperture.
 The smaller the f-stop number, the larger the
aperture.

5. Focal Length
 Focal length is the distance from the
optical center of the lens to the front
surface of the camera’s imaging device
at which the image appears in focus
with the lens set at infinity.

6. Depth of Field
 Depth of field is the area in which all objects,
located at different distances from the
camera, appear in focus. Depth of field
depends on the focal length of the lens, its f-stop
and the distance between the object and
the camera.