Phytec FireWire-CAM-011H, Manual

Page: 53 / 87

The Camera in Detail
© PHYTEC Messtechnik GmbH 2006 L-680e_1
47
The actual resolution that can be achieved is usually smaller, since
the quality of the lens and some technical characteristics of the
camera (e.g. the band width of the analog amplifier) also play a
role. With color cameras in single chip technology, you must also
consider that the pixels have color filters, which also reduce the
resolution (primarily the local resolution of the color information).
The actual resolution of a system (lens – camera) can be
determined automatically and is given in terms of so-called
TV-
lines
. This is the number of perpendicular black/white lines per
screen window that can be differentiated.
•
Minimum Object Distance
The minimum object distance (M.O.D.) determines the minimum
distance between the object and the lens at which the picture can
be rendered in focus.
The M.O.D. value is given in the lens data.
An input M.O.D. = 0.3 m means that the object has to be at least
30 cm from the lens.
Often the camera has to be brought closer to the object than the
M.O.D. will allow for technical reasons. In this case you can use
an extension ring. The extension ring is inserted between the
camera and the lens and reduces the M.O.D. value. Since it is
difficult to calculate the required length of the extension ring,
extension ring sets are available (PHYTEC order number AZ005),
that can be used to achieve the required value in application.
•
Aperture
A lens with a manually adjustable aperture (iris) offers two
advantages:
1. The depth of field can be adjusted. By closing the aperture the
distance range in which objects are shown in focus is increased.
This is of particular importance if the object distance is very
small. However the amount of light allowed through by the lens is
reduced which means that exposure times will increase and/or the
picture will be noisy.