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CA-D6-xxxxW User’s Manual
21
DALSA INC.
03-32-00225-06
Light Sources
Keep these guidelines in mind when setting up your light source.
•
Halogen light sources generally provide very little blue relative to IR.
•
Fiber-optic light distribution systems generally transmit very little blue
relative to IR.
•
Some light sources age; over their lifespan they produce less light. This aging
may not be uniform—a light source may produce progressively less light in
some areas of the spectrum but not others.
Filters
CCD cameras are often very responsive to infrared (IR) wavelengths of light. If
you wish to exclude IR, use a “hot mirror” or IR cutoff filter that transmits visible
wavelengths but does not transmit wavelengths over 700
µ
m. Examples are the
Schneider Optics™ B+W 489, which includes a mounting ring, the CORION™
LS-750, which does not include a mounting ring, and the CORION™ HR-750
series hot mirror.
Lens Modeling
Any lens surrounded by air can be modeled for camera purposes using three
primary points: the first and second principal points and the second focal point.
The primary points for a lens should be available from the lens data sheet or from
the lens manufacturer. Primed quantities denote characteristics of the image side
of the lens. That is, h is the object height and h
′
is the image height.
The focal point is the point at which the image of an infinitely distant object is
brought to focus. The effective focal length (f
′
) is the distance from the second
principal point to the second focal point. The back focal length (BFL) is the distance
from the image side of the lens surface to the second focal point. The object
distance (OD) is the distance from the first principal point to the object.
Figure 9. Primary Points in a Lens System
Magnification and Resolution
The magnification of a lens is the ratio of the image size to the object size:
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