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R5906897 /02
Prometheus III
71
6.6 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 Prometheus III 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.
S
C
R
E
E
N
DMD
Lp1
Lp2
Fr1
Fr2
Image 6-13
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
”
)
Summary of Contents for Prometheus III
Page 1: ...ENABLING BRIGHT OUTCOMES Installation manual Prometheus III...
Page 8: ...R5906897 02 Prometheus III 8...
Page 32: ...R5906897 02 Prometheus III 32 Installation process...
Page 62: ...R5906897 02 Prometheus III 62 Physical installation stand alone cooler...
Page 80: ...R5906897 02 Prometheus III 80 Lenses lens holder...
Page 98: ...R5906897 02 Prometheus III 98 Input communication...
Page 100: ...R5906897 02 Prometheus III 100 Installing a HDD into the ICMP ICMP...
Page 132: ...R5906897 02 Prometheus III 132 Communicator Touch Panel...
Page 148: ...R5906897 02 Prometheus III 148 Removal and installation of the projector covers...
Page 152: ...R5906897 02 Prometheus III 152 Preventative maintenance actions...
Page 170: ...R5906897 02 Prometheus III 170 Convergence...
Page 176: ...R5906897 02 Prometheus III 176 Color calibration...
Page 199: ...R5906897 02 Prometheus III 199 Environmental Information...