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Distortion from a projector

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3 replies to this topic

#1 of 4 OFFLINE   Bobofbone


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Posted January 06 2011 - 10:45 AM

I'm considering where to place a projector for a room that will be, when finished, about 21'x11', with a height of around 8.5'. I'm planning on placing a DIY screen on the long wall, projecting across the width of the room. The house is currently under construction. The adjacent room will be a study. I have the option of ceiling mounting a projector in this room, projecting the beam through optical glass in a sealed port through the wall. I've got a few things to work around-like a drain pipe and studs. Mounting the projector in the next room will allow me to increase the throw distance, eliminate projector noise from the viewing area, and avoid placing the projector in a small space that could contribute to overheating. Since the ceiling in both rooms will be high enough, I can also position the projector (and inital projection beam) high enough to walk under it. My question: I plan to angle the glass in the port slightly to minimize reflections, use vertical shift and probably some horizontal shift to center the image on the screen. Will shifting the image as I plan, within the manufactures limits distort the image on the screen?

#2 of 4 OFFLINE   Jason Charlton

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Posted January 07 2011 - 01:57 AM

Using horizontal or vertical lens shift on front projectors does not introduce any distortion to the projected image.

Only keystone correction (which corrects a trapezoidal shape resulting from tilting the projector up or down) can degrade the image somewhat due to the digital image processing that is required to correct the natural distortion.

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#3 of 4 OFFLINE   chuckg


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Posted January 07 2011 - 04:46 AM

What Jason said.  The lens shift technique was introduced to eliminate distortion.  Know those old, bellows-type cameras?  The lenses could shift all sorts of ways to get better focus and decrease distortion.  Probably every movie projector in every cinema uses at least a little lens shift.
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#4 of 4 OFFLINE   Bobofbone


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Posted January 07 2011 - 10:40 AM

Thank you. That gives me considerable latitude in mounting a projector. I never realized it was used in commercial theaters, but when I think about how most stadium type theaters are arranged and how most theaters used to use multiple projectors and switched reels in the middle of the movie, some lense shift would have to be used.

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