Festo SBO***-Q Series, Manual

Page: 33 / 256

1. System overview
1-15
Festo P.BE-SBO-Q-EN en 1602e
Determination of the
appropriate focal length Somewhat more expensive lenses with adjustable aperture
angle (zoom) enable you to adapt the field of view to your
requirements. Lenses with fixed focal length are less
expensive.
The suitability of a lens depends on:
– the smallest possible distance which can still be
represented sharply (Minimum Object Distance - MOD)
– the focal length
– the luminous intensity
– the 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.
The following equation describes the distance between the
so-called main level and the object to be depicted. With a thin
lens the main level is the centre of the lens. With a standard
lens the position of the main level cannot be ascertained so
easily. As an estimate you can assume the centre of the lens
to be the main level.
Formula Description
f
g
G = B - B
__ .
g : Object distance (working distance)
G : Object size (size of field of view)
f : Focal length
B : Image or sensor size
1)
1)
The horizontal size, B, of the sensor is:
– for SBO...-Q-R1...
6.61 mm
– for SBO...-Q-R2... 8.60 mm
– for SBO...-Q-R3... 4.51 mm
Tab. 1/6: Calculation formula