Image Engineering
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3.3.1
Camera position and suitable lenses
Place the camera in front of the diffractive optical element located in the circular opening on the front of
GEOCAL / GEOCAL XL.
The camera can be placed directly in front of the DOE; no minimum distance is needed (view Figure 3
below). The principal axis of the lens should be aligned approx. perpendicular to the DOE. Achieve this by
aligning the 0
th
diffraction order, the brightest spot in the grid center, with the center of the image. See
Figure 4 for reference. Make sure that the point grid covers the whole image and that the border of the
DOE is not visible.
The top side of GEOCAL / GEOCAL XL and the top side of the camera must have the same orientation.
A rotation of the camera around the optical axis of approx. +/- 2° will be tolerable.
No further alignment steps are necessary. The camera's translation does not influence the mapping of the
light points. The camera rotation to the DOE is part of the calibration and is determined during the
process and reported as part of the result.
The lens's front element must not be larger than 77 mm in diameter for GEOCAL or 155mm for GEOCAL
XL to capture the point grid in full format.
Figure 3: Setting the distance between camera and GEOCAL
/ GEOCAL XL
Figure 4: Good alignment (0
th
order in center of image) Bad alignment (0
th
order far off center)
