Specifications

214
5.1 Imaging Performance by Camera’s Optical Operability
Soiled camera filter
If the camera filter inside the case is soiled or scratched, the captured image will lose its sharpness,
making the symbols difficult to read. If the filter is soiled with oil, finger prints, etc., wipe the
filter with a soft, damp cloth to avoid damaging the filter surface.
Focal plane and depth of field
As with a fixed-focus camera this imager has a limited range in which it can produce a sharp
image. The subject plane in which the camera can produce a sharp image is called the focal plane,
the distance from the camera’s device surface to the focal plane is called the focal distance, and
the range within which the subject remains sharp and in focus is called the depth of field.
The focal distance of the imager incorporated into the terminal, is 18 cm (or 7 inches), and the size
of the focal plane is 8 cm x 11 cm.
The depth of field is generally formed by two distances, one of which (near side) is calculated as
one third of the focal distance in the outward direction and the other (far side) is calculated as two
thirds of the focal distance in the inward direction. Accordingly, the depth of field of the camera
is:
Near side : 18 x (1-1/3) = 12 cm
Far side : 18 x (1+2/3) = 30 cm
However, this range varies with the ambient brightness - it becomes smaller than that calculated
above if the image is captured in a dark place.
Depth of field
Focal distance
Focal plane
Fig. 5.1