Optical Interface; Illumination; Light Sources; Filters - Dalsa Piranha 3 Series User Manual

Piranha 3 User Manual

4.2 Optical Interface

Illumination

The am ou nt and w avelengths of light requ ired to captu re u sefu l im ages d epend on the
particu lar application. Factors inclu d e the natu re, speed , and spectral characteristics of
objects being im aged , exposu re tim es, light sou rce characteristics, environm ental and
acqu isition system specifics, and m ore. Teled yne DALSA's Web site, here, provid es an
introd u ction to this potentially com plicated issu e. See ―Rad iom etry and Photo
Responsivity‖ and "Sensitivities in Photom etric Units" in the CCD Technology Prim er
fou nd u nd er the Application Su pport link.
It is often m ore im portant to consid er exposu re than illu m ination. The total am ou nt of
energy (w hich is related to the total nu m ber of photons reaching the sensor) is m ore
im portant than the rate at w hich it arrives. For exam ple, 5J/ cm
exposing 5m W/ cm

Light Sources

Keep these gu id elines in m ind w hen setting u p you r light sou rce:
•
•
•
•

Filters

CCD cam eras are extrem ely responsive to infrared (IR) w avelengths of light. To prevent
infrared from d istorting the im ages you scan, u se a ―hot m irror ‖ or IR cu toff filter that
transm its visible w avelengths bu t d oes not transm it w avelengths over 750nm . Exam ples
are the Schneid er Optics™ B+W 489, w hich inclu d es a m ou nting ring, the CORION ™ LS-
750, w hich d oes not inclu d e a m ou nting ring, and the CORION ™ H R-750 series hot
m irror.

Lens Modeling

Any lens su rrou nd ed by air can be m od eled for cam era pu rposes u sing three prim ary
points: the first and second principal points and the second focal point. The prim ary
points 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 characteristics 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 point 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 principal point to the
second focal point. The back focal length (BFL) is the d istance from the im age sid e of the
Teledyne DALSA
All manuals and user guides at all-guides.com
2
for 1m s ju st the sam e as exposing an intensity of 5W/ cm
LED light sou rces are relatively inexpensive, provid e a u niform field , and longer life
span com pared to other light sou rces. H ow ever, they also requ ire a cam era w ith
excellent sensitivity, su ch as the Piranha 3 cam eras.
H alogen light sou rces generally provid e very little blu e relative to IR.
Fiber-optic 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 span they prod u ce less light. This aging m ay
not be u niform —a light sou rce m ay prod u ce progressively less light in som e areas of
the spectru m bu t not others.
65
2
can be achieved by
2
for 1s.
03-032-10216-06