Useful lens calculations
Examples of lens calculations
Use the information in Appendix A at the end of this Reference Guide to identify the exact lens needed.
for WUXGA and 1080p
Image size 1024 x 768 pixels, screen width 6.5m, throw distance 18m from the outer end of the lens.
• Throw ratio factor (TRF) = 1920 / 1024 = 1.875
• Throw ratio required = 18 / (6.5 x 1.875) = 1.48
Choose the 1.39 - 1.87 : 1 zoom lens.
for SX+
Image size 1024 x 768 pixels, screen width 6.5m, throw distance 18m from the outer end of the lens.
• Throw ratio factor (TRF) = 1400 / 1024 = 1.37
• Throw ratio required = 18 / (6.5 x 1.37) = 2.02
Choose the 2.0 - 2.77 zoom lens.
Throw distance
Throw ratio x TRF
Screen width =
Screen width x Throw ratio x TRFThrow distance =
Notes
The throw ratio for a particular lens
is xed, but assumes that the image
lls the width of the DMD.
For images that do not ll 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.
The DMD width is 1920 for WUXGA
and 1080p projectors, and 1400 for
SX+ projectors.
Throw distance calculations are
based on the distance from the outer
end of the lens, which will vary from
lens to lens. Once a lens has been
chosen, the gures can be checked
using the lens extension values
given in Appendix A at the end of
this document.
DMD width
Image width in pixels
TRF =
Throw distance
Screen width x TRF
Throw ratio =
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