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# The Concept of Projection Ratio and the Practical Application of Projection Ratio in the Project

The Concept of Projection Ratio and the Practical Application of Projection Ratio in the Project
Throw ratio = projection distance / screen width. The projection distance refers to the distance from the projector lens to the projection screen, and the screen width is the horizontal width of the screen when the projector is in front projection.

The projection ratio calculation formula can obtain the following two formulas through deformation, projection distance = picture width × projection ratio, picture width = projection distance / projection ratio. In the project, we need to flexibly use the three formulas according to the actual situation.

Next, I will use a simple example to do the analysis for everyone. Taking a single machine as an example, we learned that the customer wants to project a 130-inch screen. The installation distance (projection distance) on the customer's site is between 2-2.5 meters.

How many machines should be recommended to the customer? There are two important data here 130 inches and the projection distance is 2-2.5 meters. 130 inches means that the diagonal length of the picture is 130 inches, 1 inch ≈ 2.54 cm, so we can know that the diagonal length of the picture is 130 × 2.54 ≈ 330.2 cm = 3.302 meters. Because different projectors have different resolutions and different aspect ratios, the width and height of 130-inch screens projected by projectors with different resolutions are naturally different. In the previous course, we learned that the WUXGA resolution is 1920 × 1200, and the aspect ratio is 1920: 1200 = 16: 10; similarly we can see that the WXGA aspect ratio is 16:10, the 1080P aspect ratio is 16: 9; 4: 3.

Through mathematical knowledge, we can calculate the width and height of the 130-inch screen under different aspect ratios. The 16: 9 130-inch is 2.878 meters wide and 1.619 meters high. At 16:10, it is 2.8 meters wide and 1.75 meters high. At 4: 3, it is 2.64 meters wide and 1.98 meters high. Therefore, it can be concluded that if the 1080P laser projector short throw (16:9) is selected, the projection ratio is 0.694 (2 ÷ 2.878≈0.694) -0.868 (2.5 ÷ 2.878≈0.868). Similarly, the machine projection ratio of WXGA or WUXGA is 0.714-0.892. XGA's machine projection ratio is 0.757-0.946.

To sum up, DHNDU610ST, DU710ST, DM630ST and DM730ST with resolution of WUXGA projection ratio of 0.79 or XGA projection ratio of 0.82; if the selected projector is DM730ST, projection distance = screen width × projection ratio = 2.64 × 0.82≈2.16 meters. That is, keep the projector lens position 2.16 meters away from the curtain when installing. The fixed point of the hanger is generally based on 2.16 meters, plus the length of the projector's half length. Of course, the actual projected picture will not be exactly rectangular as calculated theoretically, so the actual installation projection distance should be greater than the calculated distance. Then through the exclusive geometric correction function of DHN projector, the picture is fine-tuned to the ideal state.
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