Pelco Manual C2915M-E (08/05) [ 15 ]
Back Focus Adjustment
Before adjusting the back focus on a CC3770 camera equipped with an auto-iris lens, apply an external ND 3.0
filter. Using this filter drives the lens to its most open position, reducing the depth of field to its worst-case
condition. The ND filter also attenuates the light levels so that the camera switches to night (black-white mode)
after a delay of about 10 seconds. Once the lens is wide open and the camera has switched to black-white
mode, the lens/camera combination can be critically focused to the scene. If this procedure is not followed, an
apparent focus shift may be encountered when the camera switches from day (color) mode to night (black/
white) mode.
The back focus adjustment is located at the front of the camera and is accessible from either side of the case.
To adjust the back focus:
1. Loosen the two back focus locking screws (one on each side).
2. Turn the back focus ring counterclockwise until the CCD sensor assembly is as far away from the back
of the lens as possible.
3. Switch the camera from day to night mode, then back to day mode.
4. Turn the back focus ring clockwise until focus is achieved. Confirm that focus is correct by switching
between day and night mode.
5. When the back focus adjustment is satisfactory, tighten the locking screws. Do not over-turn or force the
back focus adjustment ring.
NOTE: Always turn the back focus ring such that during focussing, the CCD sensor assembly is brought
towards the back of the lens (that is, clockwise). If the point of best-focus is passed, repeat the back focus
procedure from step 2.
Figure 8. Back Focus Adjustment