Genie Monochrome Series-GigE Vision Camera
Technical Specifications
107
Optical Considerations
This section provides an overview to illumination, light sources, filters, lens modeling, and lens magnification. Each
of these components contribute to the successful design of an imaging solution.
Illumination
The amount and wavelengths of light required to capture useful images depend on the particular application. Factors
include the nature, speed, and spectral characteristics of objects being imaged, exposure times, light source
characteristics, environmental and acquisition system specifics, and more. The DALSA Web site,
http://mv.dalsa.com/
, provides an introduction to this potentially complicated issue. Click on Knowledge Center and
then select Application Notes and Technology Primers. Review the sections of interest.
It is often more important to consider exposure than illumination. The total amount of energy (which is related to
the total number of photons reaching the sensor) is more important than the rate at which it arrives. For example,
5
J/cm
2
can be achieved by exposing 5mW/cm
2
for 1ms just the same as exposing an intensity of 5W/cm
2
for 1
s.
Light Sources
Keep these guidelines in mind when selecting and setting up light source:
LED light sources are relatively inexpensive, provide a uniform field, and longer life span compared to other
light sources. However, they also require a camera with excellent sensitivity.
Halogen light sources generally provide very little blue relative to infrared light (IR).
Fiber-optic light distribution systems generally transmit very little blue relative to IR.
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.
