Dalsa Spyder3 GigE, User Manual

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Spyder3 Color Manual 21
DALSA 03-032-20059-01
3.2 Optical Interface
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. DALSA‘s Web site http://mv.dalsa.com, provides
an introduction to this potentially complicated issue. See ―Radiometry and Photo
Responsivity‖ and "Sensitivities in Photometric Units" in the CCD Technology Primer
found under the Application Support link.
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 5 mW/cm
2
for 1 ms just the same as exposing an intensity of 5 W/cm
2
for 1

s.
Light Sources
Keep these guidelines in mind when setting up your 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, such as the Spyder3 Color camera.

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; 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.
Blue Clipping: In most photodiodes, including those in the CCD used in the Spyder 3
Color, the blue color is the least responsive. As a result, in order to maintain white
balance the blue color has to be gained up approximately 2 to 3 times more than the red
or the green colors. When the user issues a command, such as scg 20 (i.e. gaining up all
colors to 20 dB), the total blue gain will max out between 15 dB and 19 dB as a result of it
already being gained higher by default (i.e. in the 0 dB gain setting).
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 750 nm. 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.