DEK 265 horizon Engineering Specification page 13

Chapter Issue 1 May 00
Variations in the distance between the optic unit and the board fiducials due to
uneven board surface are transparent when using telecentric lenses. With a
standard lens the diameter, centroid and position of a fiducial varies with this
distance, hence key elements in determining alignment of the board vary
depending on where the fiducials lie in the field of view.
Conventional Lens
If the board to camera distance varies due
to uneven board surface, the position and size
of the fiducial will vary accordingly.
Lens
Without DEK's use of telecentric lenses, a pre-alignment stage would have to be
added to bring the fiducials into the centre of the field of view, before carrying
out a final alignment stage.
Engineering Specification
ENGINEERING SPECIFICATION
Telecentric Lenses Array
Telecentric Stop
KEY FEATURES
All fiducials seen as
identical wherever they
appear in the field of view.
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