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8.3.9.1 Low Light Applications
If a low-light application requires that a very small amount of light creates a significantly large
video output, then an increase of the video gain may be required. Note: the increased video gain
will create a more sensitive camera, but the noise in the image will increase !
8.3.9.2 Large intra-scene Dynamic Range
An application may produce plenty of light, but the purpose of the application might be to discern
image details in the bright part of an image as well as in the relatively darker parts of the image.
A low gain setting will be useful in imaging the entire dynamic range.
8.3.9.3 Automatic Light Control
If an application has to deal automatically with variable light conditions, a camera with the AGC
(automatic Gain control) may be suitable. This could be made to work with the Auto-Iris feature
to provide an increased range of light variation.
See section 5.4 for More Details on Gain/Offset control
8.3.10 How is the “Back Focus distance” set on DVC’s DigitEyes cameras ?
The Back Focus distance is the distance from the back of the lens system to the surface of the
CCD. Most “security and surveillance” cameras use inexpensive rubber tipped set screws to
hold the C-Mount ring and thus set the back focus distance! While this works well for security
and surveillance applications, it is not recommended for high-end image processing
applications.
In order to achieve opto-mechanical stability and repeatability, a different approach was taken in
the design of the opto-mechanical sub-system of the DigitEyes cameras. The C-Mount ring (into
which the C-Mount lens is screwed in) itself screws into an outer ring. A “lock nut” or
“compression ring” that screws onto the outer thread of the C-Mount ring is then used to lock
down the C-Mount ring.
In order to set the Back Focus distance:
1) Screw in the lens till it is tightly set in the C-Mount ring.
2) With the power supply connected and the output of the camera connected to a monitor, point
the lens of the camera at a distant scene; use sufficient ND filters so that the iris of the lens is
wide open and the image (on the monitor) is not saturated.
3) Set the focus distance of the lens to infinity (
∞
).
4) Loosen the lock nut of the DVC camera.
5) Unscrew (or screw in) the lens and the C-Ring together until the image of the distant scene
comes into sharp focus.
6) Tighten the lock nut; the Back Focus distance is now set for the lens! Changing the lens may
require re-adjusting the Back Focus distance.
Summary of Contents for DigitEyes Series
Page 14: ...9 Figure 4 3 TC 245 Gate Level Drawing Texas Instruments 1994 ...
Page 61: ...56 12 Appendix D Camera Mechanical Drawings Figure 12 1 Camera Mechanical Drawings ...
Page 63: ...58 Figure 13 2 Camera Noise Spectrum Min Gain Bandwidth 10kHz to 4 2MHz ...
Page 64: ...59 Figure 13 3 Camera Noise Spectrum Max Gain Bandwidth 100kHz to 4 2Mhz ...
Page 65: ...60 Figure 13 4 Camera Noise Spectrum Max Gain Bandwidth 10kHz to full ...