User`s manual

Preliminary
Genie Monochrome Series-GigE Vision Camera Technical Specifications • 95
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://vfm.dalsa.com/, provides an introduction to this potentially complicated
issue. Click on the Application Support link and then select the CCD Technology Primer. Review
“Radiometry and Photo Responsivity” along with other 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, 5μJ/cm
2
can be achieved by exposing 5mW/cm
2
for 1ms just the same as
exposing an intensity of 5W/cm
2
for 1μs.
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.