PG-MB60X. Version 1.2 - Sharp Projector Handy Guide. Page 20

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Consider the following triangle in relation to your screen

The most common image format for CTV, PC and projected images is 4:3 (4 by 3). This is
also known as the image aspect ratio. This means that the height measurement is ¾ that of
the width. Using the 3-4-5 triangle rule, the diagonal measurement can be used to calculated
width.

Examples 

Diagonal = 10m Width = (Diagonal ÷ 5) x 4  = 10 ÷ 5 x 4 = 8m
Height = 6m   Width = (Height ÷ 3) x 4  = 6 ÷ 3 x 4 = 8m

Although 4:3 is a popular aspect ratio there are others:

5:4
Some PCs are able to produce SXGA images, which offer a resolution of 1280 dots
horizontally by 1024 dots vertically. This aspect ratio is 5:4 

16:9 and 21:9
The majority of DVD format films are now mastered in Wide-Screen format, of which there are
two popular aspect ratios; 16:9 and 21:9. Sometimes these ratios are quantified with respect
to 1, so expect to see 1.85:1 and 2.35:1 respectively.

Knowing the diagonal measurement, calculating the screen width with these other ratios can
be done in a similar manner.

For 5:4 (1.25:1) Width = (Diagonal ÷ 6.403) x 5
For 16:9 (1.78:1)

Width = (Diagonal ÷ 18.358) x 16

For 21:9 (2.35:1)

Width = (Diagonal ÷ 22.847) x 21

 

Focal Length
This is the distance between the display panel and the focal point. The focal length is usually
printed on the lens ring and is usually preceded with a lower case f. If it is a zoom lens then
two figures will be present, one each for the maximum and minimum zoom. eg. f=32.5-44mm.
This figure can be used to calculate the image size and throw distance values if the size of
the display panel is known.