Dalsa Genie HM640, User Manual

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114

Technical Specifications Genie HM-HC Series-GigE Vision Camera
Example: An acquisition system has a 512 x 512 element, 10

m pixel pitch area scan camera, a lens with an
effective focal length of 45mm, and requires that 100

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).
OD
mm
m
m 45
100
10



) 450 . 0 ( 450 m mm OD

Lens Selection Overview
Vision component suppliers and system integrators will have detailed information on lens products at different price
points, relative to quality and for different imaging situations. This section provides a general overview to selecting
a lens for the Genie HM.
The first two lens parameters are based on correctly matching the lens to the Genie HM model. Genie HM is
available with either a C-mount or CS-mount (two standards for flange-focal length), plus one of three sensor sizes.
These items are covered first followed by brief information on other lens parameters to consider.
Lens Mount
As shown in " Mechanical Specifications " on page 103 Genie comes in C-mount and the CS-mount. The CS-mount
is a standard with a shorter flange-focal length for space sensitive applications. The C-mount Back Focal Distance is
17.52 mm while CS-mount Back Focal Distance is 12.52 mm. The lens selected must be for the Genie mount used,
else it may not be able to focus on the target.
Lens Sensor Size
An important lens parameter is its sensor size which defines the largest camera sensor usable with that lens before
vignetting occurs (exposure that shades off gradually at the image edges). The lens size specification is in imperial
units for historical reasons, and does not directly describe the sensor diameter (even after conversion to metric).
The following figure shows different lens size standards relative to the maximum camera sensor they will properly
expose. The lens sensor standard (in imperial units) and the sensor diameter in millimeters are the two important
parameters when choosing a lens. The second figure below shows vignetting when a lens for a smaller sensor is
used.