page 73
Digital Projection HIGHlite Cine 330 3D Series
Reference Guide
CHOOSING A LENS
Rev E August 2014
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.
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 1.45 - 1.75 : 1 zoom lens
.
Throw distance
Throw ratio x TRF
Screen width =
Screen width x Throw ratio x TRF
Throw distance =
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.
The DMD width is 1920.
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 figures 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 =
