Dalsa Piranha 2 Series, Руководство пользователя

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48 Piranha 2 User’s Manual
03-032-00493-14 Teledyne DALSA
Light Sources
Keep these gu id elines in m in d w hen setting u p you r light sou rce.
• LED light sources are relatively inexpensive, prov ide a uniform 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 Piranha 2 cam era.
• Halogen light sources generally provide very little blu e relative to 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 m ay
not be u niform —a light sou rce m ay p rod u ce p rogressively less light in som e areas 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 avelength s bu t d oes not tran sm it w avelengths over 750nm . Exam p les
are the Schneider Optics™ B+W 489, which includes a m ounting 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 p u rp oses u sing three p rim ary
p oints: the first an d secon d p rincip al p oints and the secon d focal p oint. The p rim ary
p oints for a len s sh ou 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. Th at
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 in finitely d istant object is brou ght to
focu s. The effective focal length (f

) is the d istan ce from the second p rincip al p oint to the
second focal p oint. The back focal length (BFL) is the d istan ce from the im age sid e of the
lens su rface to the secon d focal p oint. The object distance (OD) is the d istance from the first
p rincip al p oint to the object.
Figure 11. Primary Points in a Lens System
Magnification and Resolution
The m agnification of a len s is the ratio of the im age size to the object size:
m
h
h


where m is the magnification, h’ is the image height (pixel size)
and h is the object height (d esired object resolu tion size).
By sim ilar triangles, the m agnification is alternatively given by:
m
f
OD


These equ ations can be com bined to give their m ost u sefu l form :
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