Figure 4-10.–Direct-vision range finder focusing.
focus knob, until the double images coincide and only
in the direct-vision range finder system. Everything
one image is seen (fig. 4-10).
appears sharp through the viewfinder window.
The disadvantages of a direct range finder system
are that it does not couple to a large variety of lenses,
thus restricting its use to only several different
focal-length lenses. Unlike the ground glass and SLR
focusing systems, depth of field cannot be determined
Autofocus
Most autofocus cameras use the same principle as a
direct-vision range finder camera. The autofocus
camera determines the subject distance by comparing
4-8
