the lens and the film. When light rays come from a far
object and pass through a lens, they form a sharp image
close to the lens. When light rays come from a near
object, they form an image farther away from the lens.
This means that the lens must be focused on either the
When you want a sharp image of the far object, move
the lens closer to the film (fig. 1-26).
images of points composing the subject. After light
strikes a subject, it is reflected from many points on the
subject. A camera lens redirects these reflected rays into
corresponding points on the film. Each of these points
is reproduced by the lens as a circle. When the circle is
smaller than l/100 inch, it appears as a sharp point to
the eye. When the circle is larger than 1/100 inch, the
eye sees it as a circle, and the image is blurred or out of
focus. Each out-of-focus circle on the film is called a
circle of confusion and can be visualized as the cross
section of a cone of a light ray (fig. 1-27).
Basic Photography Course