Swann PRO-781 Manual page 5

FOCUS: The left hand dial controls the focus (see diagram, opposite).
Adjusting the focus control is kind of like trying on a different pair of glasses -
it can make sharp things look blurry and blurry things look sharp. It's not quite
magic, but it's pretty close.
Basically, once you've set the zoom, twist the focus knob until what you want to
see doesn't look blurry anymore. If you can't turn the knob any more one way, go
back the other.
You can only have so much in focus at once - photographers refer to the size of
the area in focus as the "depth of field".
The diagram to the lower right shows a couple of different focusing options. The
shaded areas represent the depth of field. As you can see, there is no hard edge,
some things are "more" in focus than others.
Note that this is for illustrative purposes only - there are many factors which
contribute to depth of field which vary from location to location.
A: The lens is at its widest, and
focused on an area relatively close to
the camera. The depth of field is quite
large.
B: The lens at its widest with focus set
to "infinity". Anything in the shaded
section will be in focus, and this focus
extends to infinity (that is, things in
the far distance will also be in focus).
However, things in the distance might
be too small to see the detail you
require.
C: The lens at its tightest, focused
on an area close to the camera. As
you can see, the more the lens is
zoomed, the smaller the depth of field
becomes.
D: The lens at its tightest with focus
further from the camera. At this
distance, the actual depth of field is
much larger, but it doesn't extend to
infinity like it does when the lens is
wide.
A
B
C
D
5