Choosing a lens Digital Projection Ltd. E-Vision Laser 13000 WU Series
Full lens calculation
Introducing TRC
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.
The choice of lens will affect the image size and will address discrepancies between the DMD™
resolution and the source.
When an image fills 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 16:9 display
When a 16:9 projector is used for a 4:3 image, the image does not fill 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 fills 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 fill 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 fill the 4:3 screen seamlessly
Reference Guide
Rev A June 2019
page 97
Notes
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