DF4510HD | DF4910HD | DDF4510HDV-IM/-SM | DDF4910HDV-IM/-SM
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6.1.3
Back Focus
The back focus (focal flange length) is the distance between the rear lens element and
the image sensor. Optimum focus is only possible if the correct distance is set.
Generally, the back focus is optimized ex factory for all CS mount lenses offered by
Dallmeier.
However, due to production tolerances of lenses it may be necessary to adjust the back
focus in individual cases.
If the optimum focus cannot be set exactly for lenses with a fixed focal length or if the
focus changes as the focal distance of zoom lenses (not varifocal lenses) changes, pro
-
ceed as follows:
First, ensure a clean and nearly dust-free environment.
Hold the camera with the image sensor area facing downward so that no dust will get
into the camera or onto the image sensor.
During the following steps, always beware not to touch the sensor or sensor glass, the
rear lens element or other glass elements inside of the camera in order to avoid dam-
ages due to scratching or loss of image quality due to fingerprints.
Carefully unscrew the used lens from the camera in a counter-clockwise direction (first
unplug the DC auto iris 4-pin connector if necessary).
Loosen the locking screw of the back focus adjustment ring.
Unscrew the back focus adjustment ring.
Remove the attached spacer ring from the back focus adjustment ring.
Screw the back focus adjustment ring back onto the camera.
Tighten the locking screw of the back focus adjustment ring.
If necessary, remove dust from the sensor glass, the rear lens element or other glass
elements in the camera using a suitable bulb blower.
However, beware not to disperse dust particles inside the camera.
Do not use canned air.
Do not use organic solvents (alcohol, benzine) or cotton buds for cleaning.
Finally, screw the lens carefully back onto the camera in a clockwise direction and
tighten it without using excessive force.
Ensure that the lens thread does not get stuck and the lens is not tightened too firmly
to avoid damages to the thread.
If necessary, adjust the back focus using the back focus adjustment ring (see below).
To adjust the back focus, the iris of the lens must be open as wide as possible (smallest
iris value). For lenses with automatic iris control, you will require a ND filter (grey filter) to
prevent the iris from closing in bright light.
