Full lens calculation
Introducing TRC
The choice of lens will affect the image size and will address discrepancies between the
DMD™ resolution and the source.
When an image lls the height of the DMD™ but not the width, it uses less than 100% of
the DMD™ surface. A lens chosen using the basic formula may produce an image that is
considerably smaller than the actual screen.
To compensate for loss of screen space in such situations, you need to increase the throw
ratio using a Throw Ratio Correction (TRC).
Example
Fig. 1 illustrates a 4:3 image within a 1080p DMD™.
When a 1080p projector is used for a 4:3 image, the image does not ll the width of the
DMD™, creating a pillarboxing effect - blank spaces to the left and right.
Fig. 2 shows the same image projected on a 4:3 screen using a standard lens (chosen with
the basic calculation).
The DMD™ accurately lls the width of the screen; however, the pillarboxing is now part of the
projected image and is transferred to the screen.
The DMD™ does not ll the height of the screen, which has caused letterboxing - further
blank spaces at the top and bottom of the screen.
The image is now surrounded by blank space, which can be removed if the throw ratio is
increased.
Fig. 3 shows the image projected on the same screen with a lens chosen using TRC.
The increased throw ratio has allowed the 4:3 image to ll the 4:3 screen seamlessly.
Notes
TRC can only be applied if greater
than 1. If TRC is 1 or less, disregard
it and calculate the throw ratio using
the basic formula.
You can also use the information
in Appendix B: Lens Charts to
choose a lens.
For information about individual lens
part numbers, see Appendix A:
Lens Part Numbers at the end of
this document.
Fig. 1
Fig. 2
Fig. 3
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