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The depth-of-field scale
The plane which is rendered sharpest is the plane,
parallel to the film, upon which the lens is fo-
cused. The optimum sharpness decreases pro-
gressively in front of and behind this plane so that
a certain range exists within which the image is, to
the eye, rendered sharply.
This range is termed the depth-of-field. It is de-
pendent on the focus setting, the focal length of
the lens (the two values together determine the
reproduction ratio) and the aperture. Stopping
down, i.e. selection of a larger f-number, increases
depth-of-field, while opening the aperture, i.e.
selection of a smaller f-number, decreases it.
The depth-of-field scale in conjunction with the
focusing ring indicates the range of sharpness at
the set focus distance.
For example, using the LEICA SUMMILUX-M
50mm f/1.4 lens focused at 5 meters, the depth
of field at f/4 ranges from approximately 4 to 8
meters. Stopping down to f/11 at the same focus-
ing distance, however, increases the range to
3-20 meters.
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