Piranha HS-xx RoHS User Manual
Teledyne DALSA
03-032-20013-03
27
3.3 Optical Interface
Illumination
The am ou nt and w avelengths of light requ ired to cap tu re u sefu l im ages d ep end on the
p articu lar ap p lication. Factors inclu d e the natu re, sp eed , and sp ectral characteristics of
objects being im aged , exp osu re tim es, light sou rce characteristics, environm ental and
acqu isition system sp ecifics, and m ore.
It is often m ore im p ortant to consid er exp osu re than illu m ination. The total am ou nt of
energy (w hich is related to the total nu m ber of p hotons reaching the sensor) is m ore
im p ortant than the rate at w hich it arrives. For exam p le, 5
J/ cm
2
can be achieved by
exp osing 5m W/ cm
2
for 1m s ju st the sam e as exp osing an intensity of 5W/ cm
2
for 1
s.
Light Sources
Keep these gu id elines in m ind w hen setting u p you r light sou rce:
LED light sou rces are relatively inexp ensive, p rovid e a u niform field , and longer life
sp an com p ared to other light sou rces. H ow ever, they also requ ire a cam era w ith
excellent sensitivity, su ch as the H S-xx cam era.
H alogen light sou rces generally p rovid e very little blu e relative to infrared light (IR).
Fiber-op tic light d istribu tion system s generally transm it very little blu e relative to IR.
Som e light sou rces age; over their life sp an they p rod u ce less light. This aging m ay
not be u niform —a light sou rce m ay p rod u ce p rogressively less light in som e ar eas of
the sp ectru m bu t not others.
Filters
CCD cam eras are extrem ely resp onsive to infrared (IR) w avelengths of light. To p revent
infrared from distorting the images you scan, use a ―hot mirror ‖ or IR cutoff filter that
transm its visible w avelengths bu t d oes not transm it w avelengths over 750nm . Exam p les
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
m irror.
Lens Modeling
Any lens su rrou nd ed by air can be m od eled for cam era p u rp oses u sing three p rim ary
p oints: the first and second p rincip al p oints and the second focal p oint. The p rim ary
p oints for a lens shou ld be available from the lens d ata sheet or from the lens
m anu factu rer. Prim ed qu antities d enote character istics of the im age sid e of the lens. That
is,
h
is the object height and
h
is the im age height.
The
focal point
is the p oint at w hich the im age of an infinitely d istant object is brou ght to
focu s. The
effective focal length (f
)
is the d istance from the second p rincip al p oint to the
second focal p oint. The
back focal length (BFL)
is the d istance from the im age sid e of the
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