Choosing a lens Digital Projection Ltd. E-Vision Laser 13000 WU Series
Full lens calculation example
INFORMATION YOU NEED FOR THESE CALCULATIONS
The TRC formula
The TRC table (to use instead of the formula)
2.35:1 (Scope) TRC < 1, not used
1.85:1 (Flat) TRC < 1, not used
1.78:1 (16:9) TRC < 1, not used
1.6:1 (16:10) TRC < 1, not used (native aspect ratio)
1.33:1 (4:3) TRC = 1.2
1.25:1 (5:4) TRC = 1.28
The throw ratio formula
Allow a tolerance of +/- 3% in the throw ratio calculation.
The lens table:
Throw ratios Focus range
0.377 : 1 fixed (UST) 0.82 m - 2.71 m
0.75 - 0.93 : 1 zoom 1.02 m - 12.7 m
0.76 : 1 fixed 0.81 m - 5.08 m
1.25 - 1.79 : 1 zoom 1.33 m - 11.73 m
1.73 - 2.27 : 1 zoom 1.83 m - 14.9 m
2.22 - 3.67 : 1 zoom 2.36 m - 24.2 m
3.58 - 5.38 : 1 zoom 3.8 m - 35.35 m
5.31 - 8.26 : 1 zoom 5.59 m - 54.8 m
Your screen is 4.5m wide; you wish to place the projector approximately 11m from the screen.
The source is 4:3.
1. Calculate TRC as follows:
TRC = 1.6 / 1.33 = 1.2.
2. Calculate the throw ratio:
Throw ratio = 11 / 4.5 x 1.2 = 2.04
3. Allow a tolerance of +/- 3% in the throw ratio calculation and find a match in the lens
table.
The table shows that the matching lens is the 1.73 - 2.27 : 1 zoom lens.
4. Check whether the lens covers the required throw distance.
The focus range quoted for the 1.73 - 2.27 : 1 zoom lens is 1.83m - 14.9m. The required
distance of 11 m is within the range.
Reference Guide
Rev A June 2019
page 99
Notes
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