67R5905753 /17 DPxK-19B/23B/P
5.6 Back Focal Length adjustment
When to adjust the Back Focal Length?
If a lens is used with a throw ratio suited for the application, (lens selection depends on projection distance
and screen size) typically one would NEVER need to adjust the Back Focal Length of the projector.
A Back Focal Length adjustment is only required in case the Focus range of the installed lens does not
capture the projection screen either for FLAT and/or for SCOPE. In other words, when it is impossible to focus
the image on the screen for FLAT and/or for SCOPE. Note that the lenses for the DPxK B series are varifocal.
So, switching between FLAT and SCOPE (zoom action) requires a readjustment of the focus.
What is Back Focal Length adjustment?
Back Focal Length adjustment means moving the lens plane (Lp), thus the Lens Holder front plate, closer to or
further from the DMD plane. The closer the lens plane to the DMD plane the further the focus range (Fr) of the
lens will be.
Image 5–13
Do not abuse the Back Focal Length adjustment of the Lens Holder. Neglecting this will result in
loss of image quality because of the lens design. Cases requiring Back Focal Length adjustment
normally indicate incorrect lens choice (throw ratio).
Required tools
• Nut driver 10mm.
• Allen wrench 3mm.
• Nut driver 13mm.
How to check the Back Focal Length
1. Ensure that the throw ratio of the installed lens matches with the requirements of the application
(projection distance and screen size).
2. Ensure that the correct lens parameters are activated. (See user guide of the “Communicator” chapter
Installation > Advanced > Lens parameters)
Caution: Not using the correct lens parameters could result in lens damage.
3. Perform a lens HOME & RETURN operation. (See user guide of the “Communicator” chapter Installation >
Advanced > Lens parameters)
4. Project the green focus test pattern. (screen file “no masking” or “no “crop”)
Lenses & lens holder
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