Dalsa PC-30-02K80-R, Manual

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Piranha Color Camera User’s Manual 73
DALSA 03-032-10211-03 9/27/2007
Figure 10: Primary Points in a Lens System
SECOND PRINCIPAL POINT
SECOND FOCAL POINT
f
BACK FOCAL LENGTH.
LIGHT RAYS FROM LEFT
OBJECT
HEIGHT (h)
FIRST PRINCIPAL
POINT
OPTICAL AXIS
OBJECT
DISTANCE (OD)
IMAGE SIDE OBJECT SIDE
Magnification and Resolution
The magnification of a lens is the ratio of the image 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 (desired object
resolution size).
By similar triangles, the magnification is alternatively given by:
m= f '
—
OD
These equations can be combined to give their most useful form:
h '
h
—
= f '
– OD
This is the governing equation for many object and
image plane parameters.
Example: An acquisition system has a 512 x 512 element, 10µm pixel pitch area scan
camera, a lens with an effective focal length of 45mm, and requires that 100
μ
m in the
object space correspond to each pixel in the image sensor. Using the preceding equation,
the object distance must be 450mm (0.450m).
10 µm
100 µm
— = 45 mm
OD
OD=450 mm (0.450 m) —