Camera Operation

Proper focusing leads to sharp images

The lens-to-film distance will depend on the object distance and on the focal length of the lens

The shutter is a mechanical device that is opened for selected time intervals

Most cameras have an aperture of adjustable diameter to further control the intensity of the light reaching the film

With a small-diameter aperture, only light from the central portion reaches the film, and spherical aberration is minimized

Camera Operation, Intensity

Light intensity is a measure of the rate at which energy is received by the film per unit area of the image.
 *The intensity of the light reaching the film is proportional to the area of the lens. 
The brightness of the image formed on the film depends on the light intensity.
  *Depends on both the focal length and the diameter of the lens

Camera, f-numbers

The ƒ-number of a camera is the ratio of the focal length of the lens to its diameter

ƒ-number = f/D 

The ƒ-number is often given as a description of the lens “speed”
A lens with a low f - number is a “fast” lens 

Increasing the setting from one ƒ-number to the next higher value decreases the area of the aperture by a factor of 2

The lowest ƒ-number setting on a camera corresponds to the aperture wide open and the maximum possible lens area in use

Simple cameras usually have a fixed focal length and a fixed aperture size, with an ƒ-number of about 11 (large depth of field)

Most cameras with variable ƒ-numbers adjust them automatically