Specifications are subject to change without notice.
Printed in Japan (0310) 833-53-014-30 U
TOA Corporation
URL : http://www.toa.jp/
*Focus and the ND filter
When adjusting focus, an important aspect is depth of field,
actually the depth of the focus. The term depth is used is
because we can describe it as being deep or shallow. If the
in-focus area goes well into (long distance) the subject field is
referred to as being deep. If the background area is not in
focus but the subject field is in sharp focus, the field is
referred to as being shallow.
The depth of field will change depending on the focal length
of the lens, the iris of the lens and the shooting distance. And
in surveillance cameras, the lens iris has an effect on
focusing. As the diagram makes clear, the wider the lens iris
opening size, the shallower will be the depth of field.
ND Filter
ON
OFF
Depth of field is shallow
Depth of field is deep
Why will correct focus for daytime shooting result
in an out-of-focus image when shooting at night.
If a camera having an auto iris lens is used, the lens iris
opening size remains small during daylight hours. Setting the
correct focus at this time is performed with a deep depth of
field. As day turns to night, the lens iris opening size
increases to gain more light, and the image goes out of the
perfect focus it was in.
Because surveillance cameras are in operation during the
day as well as at night, the lens iris must be kept open. The
ND filter is designed specifically for this situation. The
ND filter reduces light coming into the lens to prevent the
lens iris opening size from getting
smaller during the day. The camera's
focus must be adjusted with the ND
filter mounted in front of the lens
during the daylight to ensure the lens
iris opening size remains wide.
TOA adjustment switch makes focusing simple.
Because adjusting focus with the ND filter mounted is
inconvenient, TOA has incorporated a switch on the compact
camera can simply be switched on or off. By making the lens
iris size wide even during the day, providing easy focusing to
maintain perfect focus.