# distance from ceiling

Discussion in 'Displays' started by Darren McGruther, Jan 16, 2005.

1. ### Darren McGruther Stunt Coordinator

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In a ceiling mounted PJ setup, how far down from the ceiling should the PJ be in comparison to the top edge of the screen?. PJ is a SP4805

2. ### John Whittle Stunt Coordinator

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The number varies with the size of the screen. See the Screenplay book page 6. Other projectors are different.

The 4805 has an image offset from the center line of the lens. If you point the projector on a flat surface straight on to a wall, for an image 10 feet tall, the image will be 2.73 feet above the center line of the lens.

If you ceiling mount the projector, then it will be "down" from the centerline of the projector. The centerline of the lens is 3 inches from the bottom of the projector. If you mount (with spacers, etc) is six inches, add the three and if your picture is five feet tall, then the image will be two feet down. Of course you can tilt the projector and apply some keystone correction.

The "magic number" in the book is 127.3% which when multiplied by the screen height will give you the top of the picture from the centerline of the projector lens in normal orientation. In ceiling mount just use the 27.3% and it will give you the screen top from the centerline of the lens.

(Oh and now I just saw where I put my notes and computations for my installation!)

But far the easiest way (which I just found) is to go to the Infocus site, got to support/resources for the 4805 and load the excel calculator. You can plug in your screen gain and width and it'll give you a drawing and all the numbers. It's set for the Infocus mount, but it'll show your screen drop and you can adjust for any difference in the mount you use compared to the Infocus (made by Pearless) mount.

John

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