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The Piranha XL Camera
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.
Good
Focus
Good
Focus
Good
Focus
Worse
Focus
Worse
Focus
Worse
Focus
Worse
Focus
Figure 23 Effects of Camera Tilt In the Long Sensor Axis
A mechanical means to adjust this angle may need to be incorporated into the camera mount. This
becomes a finer, more precise adjustment as the magnification increases, especially above 1x, as
the depth of field becomes progressively smaller. The two examples below demonstrate this
characteristic.
Assume the use of a 120 mm lens set at f5.6 and Circle of Confusion = 2 pixels.
Example A: Magnification of 0.5X
Depth of Field = 1.34mm
Field of View = 16352 x 10um = 163.52mm
Requires the camera optical axis to be /-0.94
°
from perpendicular
Example B: Magnification of 2X
Depth of Field = 0.042mm
Field of View = 16352 x 2.5um = 40.88mm
Requires the camera optical axis to be /-0.12
°
from perpendicular
