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Focus
SHARPNESS or definition refers
to
the outlines of the image. When
th~se
outlines are sharp, the picture is in good focus. A camera lens is focused
by moving it
to
and from the film. On the lenses for the Cine-Kodak
Special this is accomplished by rotating the FOCUSING COLLAR until
the figure showing the distance in feet from camera
to
subject is at the
INDEX LINE (Figure 24).
REFLEX
FINDER
Fig
24
Another method of focus-
ing the Cine-Kodak Special
is
to
use the REFLEX FIND-
ER and
to
focus visually.
This
obviates
estimating
distances. Use of the reflex
finder is described on page 42.
DEPTH OF FOCUS:
When
the lens
is
focused on a given
distance, objects somewhat
nearer and farther than that
distance, will be in good
focus. This range is called
depth
of
focus or range of
sharpness.
This depth is greater the
smaller the diaphragm used.
For example, the
I-inch
f. 1.9
lens wide open, focused
a
t 6 feet,
has
a depth from S
to
7 feet
.
Objects
not in that range will be blurred.
But when
the smallest opening
(f.16)
is
used, the depth increases so that objects from
2~
feet
to
infinity
are
sharp.
When poor light conditions compel the use of a large diaphragm,
care must be taken in estimating distances
to
avoid out-of-focus pictures.
With
the
smaller openings
(f.S.6
and smaller), depth is so great that
the I-inch f.1.9 lens can be used as a "fixed-focus" lens when set on 2S
feet. Even with these small openings, however, it is necessary
to
focus
accurately for close-ups
.
Depth of focus is much less for near distances
than
for far.
27
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