The Piranha XL XDR Camera
•
69
Object
Motion
Camera Not Perpendicular
to Object Surface
Row
#1
Row
#12
Longer Optical
Path Creates
Lower Magnification
Shorter Optical
Path Creates
Higher Magnification
Row
#1
Row
#12
Higher
Magnification
Lower
Magnification
Image has sideways component
as it moves across the pixels array
Digital image will
appear smeared in
long axis of the sensor
Camera Angle
Causes Parallax
End
Pixels
End
Pixels
No sideways
component as
image moves
across the
pixels array
Figure 22 Effects of Camera Tilt in Scan Direction
Though the Piranha camera only has a maximum of 12 rows, the tolerable angle that does not
cause a parallax issue is still quite small. For example, assume that a satisfactory image quality can
be achieved with ¼ pixel sideways motion at the end pixels and a 120 mm lens with magnification
of 0.5. This would require that the camera’s optical axis to be within ± 3.5
°
from perpendicular.
Note: If you have confirmed that the camera’s optical axis is perpendicular to the material surface
and you still have difficulty focusing at the edges, then check that the lens specification for MTF
characteristics over the entire field of view. The MTF of lenses typically reduces at the edges of the
field of view.
Image Will Focus Well on One Side but Not the Other at the Same Time
If sharp focus can be achieved at only one location of the sensors field of view and progressively
gets worse from that point, then the camera may not be perpendicular to the object surface with
respect to the long axis of the sensor.
