Throw distance and lens extension
The throw distance is calculated to the outer end of the lens. The nominal
distance between the front of the projector and the outer end of the lens is
called lens extension.
Lens extension values will vary from lens to lens. Once a lens has been
chosen, the gures can be checked using the values given on the previous
page.
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.
For information about lens
extensions and individual lens part
numbers, see Appendix A at the
end of this document.
Lens extension is measured when
the lens is focused at innity, and
fully extended. At other focus
settings, the extension could be up
to 10mm less.
Lens extension measured from front of corner post
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