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page 2.13
Digital Projection LIGHTNING 35HD User Manual 2. Installation
Notes
The Throw ratio for a particular
lens is fixed, but assumes that
the image fills the width of the
DMD.
For images that do not fill the
width of the DMD, the Throw
ratio is effectively increased. To
correct for this in these
calculations, a Throw Ratio
Factor (TRF) is used.
Lens extension is measured
when the lens is focussed at
infinity, and fully extended. At
other focus settings, the
extension could be up to 10mm
less
Useful lens calculations
The following lens calculations may be useful:
Throw ratio =
Throw distance
Screen width
Throw ratio factor (TRF) =
DMD width in pixels = 2048
image width in pixels image width in pixels
Therefore:
Screen width =
Throw distance (from outer end of lens)
Throw ratio x TRF
Throw distance = Screen width x Throw ratio x TRF
The throw distance calculated above is to the outer end of the lens. For each lens,
the nominal distance between the front of the projector and the outer end of the lens
(lens extension) will be as listed below:
lens extension
1.0: 1 fixed lens 103-350 185mm (7.3in)
1.25 - 1.45: 1 zoom lens 103-351 161mm (6.3in)
1.45 - 1.8: 1 zoom lens 102-451 109mm (4.3in)
1.8 - 2.4: 1 zoom lens 102-676 97mm (3.8in)
2.2 - 3.0: 1 zoom lens 102-677 53mm (2.1in)
3.0 - 4.3: 1 zoom lens 102-678 98mm (3.9in)
4.3 - 6.0: 1 zoom lens 104-189 170mm (6.7in)
lens extension,
measured from front
of corner post