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2.12 Back Focus (Applies to 8800
The Back Focus function allows user to a have sharply focused image
all the time, including during conditions of reduced light levels.
Click on far or near buttons to adjust the camera focus accordingly. The
focus will continue to change until the button is released or until the
focus reaches the limit of its travel.
Back Focus Calibration
The back focus of a lens refers to the distance between the image sen-
sor and the lens. When the back focus is correctly adjusted, the image
will remain in focus while the lens is zoomed in and out. The wavelength
of the light illuminating a particular scene plays a significant role in de-
termining the required backfocus distance, as different wavelengths of light require different back focus
distances to be in sharp focus. For "color only" cameras, this back focus problem is minimized by using an
IR cut filter and optical coatings on the lens elements so that only the visible spectrum of light (400nm ~
700nm) is allowed to reach the image sensor, and all of the wavelengths within the visible spectrum come
into focus at the same back focus distance.
Back focus problems arise when the camera is used as a color day camera and as an IR sensitive mono-
chrome night camera. When the IR cut filter is removed, and especially if an IR illuminator is used to illumi-
nate the scene, the back focus distance must be changed to allow the image to remain in focus throughout
the zoom range. The 8800
cally change to match the cameras mode of operation and the users' particular night time lighting method.
Calibration Procedure:
Color Day Mode: The Back Focus distance for the color day mode is factory calibrated, and does not typi-
cally need to be recalibrated. However if it isnecessary, the following procedure can be used to calibrate the
Back Focus distance for the color day mode.
1. Verify that the lens extender is OUT.
2. View the color day scene in Auto Shutter mode.
3. Zoom out fully.
4. Open the iris using the manual iris control (Lens Tab, select and hold Iris Open until iris is fully
open). Note: The auto shutter will automatically compensate for all but the brightest scene il-
lumination levels. If the image is overly saturated with the iris fully open in Auto Shutter mode and
zoomed out fully, the iris will need to be closed until the image saturation is at a usable level.
5. Zoom in fully on the desired scene and adjust lens focus for sharp focus.
6. Zoom out fully.
7. Adjust Back Focus (Near and Far on Back Focus buttons) for sharp focus.
8. Select "Day" on the Back Focus button to save this Back Focus setting as the Day mode.
No Illuminator, Night Mode:
1. Verify that the lens extender is OUT.
2. While viewing the night scene, verify that the camera is locked in the Night mode (Setup>
Properties>Day/NightMode>Mono)
3. Verify the iris is fully open (Lens, select and hold Iris Open until iris is fully open)
4. Zoom in fully on the desired scene and adjust lens focus for sharp focus.
5. Zoom out fully
6. Adjust Back Focus (Near and Far on Back Focus Tab) for sharp focus. NOTE: In the event that
the scene consists of multiple light sources (Low or High Pressure Sodium, Mercury Vapor, Incan-
descent, etc.) and varied scene topography (plants, bushes, trees, buildings, etc), it is possible to
have different areas of the scene focus at different Back Focus positions. In this case the operator
will need to obtain sharp focus on the most important area of the scene.
7. Select "Night" on the Back Focus Tab to save this Back Focus setting as the Night mode
6X-1090J
)
HD
camera can be user calibrated so that the back focus distance will automati-
HD
51
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