Falcon 4M Camera Manual
Teledyne DALSA
03-032-20044-03
67
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 areas of
the sp ectru m bu t not others.
Filters
Digital cam eras are extrem ely resp onsive to infrared (IR) w avelengths of light. To p revent
infrared light 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 750 nm .
An IR cu t-off filter is recom m end ed in ord er to im p rove color im aging p erform ance, as,
in the near-IR, all the color filters allow light to p ass throu gh w hich can resu lt in ‗w ashed -
out‘ colors.
We recom m end u se of a SP700 IR-filter to rem ove u nw anted IR signal that cou ld affect
color rep rod u ction.
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 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 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
lens su rface to the second focal p oint. The
object distance (OD)
is the d istance from the first
p rincip al p oint to the object.
Figure 22: Primary Points in a Lens System
Magnification and Resolution
The m agnification of a lens is the ratio of the im age size to the object size:
m
h
h
Where m is the m agnification, h‘ is the im age height
(p ixel 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