Festo SBOC-M-R1B-H, Руководство пользователя

Страница: 27 / 88

1. System overview
1-11
Festo GDCS-SBOC-EN en 1602a
Ascertaining the suitable
focal length The somewhat more expensive lenses with adjustable open­
ing angle (zoom) enable you to adapt the field of vision to
your requirements. Lenses with fixed focal length are less
expensive. Whether a lens is suitable depends on:
– The smallest possible distance which can still be repres­
ented sharply (minimum object distance - MOD)
– Focal length
– Light intensity
– Permissible distortion.
The object distance, i.e. the distance between the camera and
the object to be photographed, can be calculated according
to the laws of optics. Please observe that the following calcu­
lation formula describes the distance between the so-called
main level and the object to be represented. With a thin lens
element, the main level is the centre of the lens. With an ob­
jective lens, the position of the main level cannot be ascer­
tained so easily. As an estimate you can assume the centre of
the objective lens to be the main level.
Formula Description
d = f * (G : B + 1) d : object distance (working distance)
G : object size (size of field of vision)
f : focal length
B : image or sensor size
1)
1) The horizontal dimension of the sensor is 6.3 mm.
Tab. 1/6: Calculation formula