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94 • Technical Specifications Genie Monochrome Series-GigE Vision Camera
• Some light sources age such that over their life span 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 extremely responsive to infrared (IR) wavelengths of light. To prevent infrared from distorting the
images you scan, use a “hot mirror” or IR cutoff filter that transmits visible wavelengths but does not transmit
wavelengths over 750nm. 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.
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:
h
h
m
'
=
Where m is the magnification, h’ is the image height (pixel size)
and h is the object height (desired object resolution size).
By similar triangles, the magnification is alternatively given by:
OD
f
m
'
=
These equations can be combined to give their most useful form:
OD
f
h
h ''
=
This is the governing equation for many object and image plane
parameters.