'new' keystone adjusting idea - diyAudio
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Old 25th September 2003, 04:42 AM   #1
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Default 'new' keystone adjusting idea

as other mentioned, tilt LCD screen can change keystone. But often part of the image will be out of focus, and with dismentled LCD monitors, moving LCD screen up and down with all the wires is not a great idea.

I just played with my newly splited fresnel lens and found that tilting method works with top half of the fresnel as well! And best of all, the imge seems in focus all cross the screen. Hope it helps.
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Old 25th September 2003, 08:46 AM   #2
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Any idea how much (in degrees) tilt could be keystone corrected buy tilting the fresnel? I haven't splitted my fresnel so I thought just to try tilting the fresnel + glass + TFT sandwich, though it might be better to separate the fresnel in the end..
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Old 25th September 2003, 01:51 PM   #3
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thats exactly how my OEM sharp xge690U projector adjusted keystone. It had a fresnel after the lcd that tilted up or down to adjust keystone... then it would be bounced off a first surface mirror and then through the lens...

so its an idea that has been proven to work.

ap0
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Old 25th September 2003, 04:52 PM   #4
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good to hear is has been used by commercial Projectors. I will try to find some simple/cheap stuff to make a keystone adjusting device
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Old 26th September 2003, 12:27 PM   #5
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Well, put your single fresnel into picture (painting) frame with a glass, shouldn't be difficult to make it adjustable.
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Old 26th September 2003, 01:40 PM   #6
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Default my thought

Ok, so I'm really rought with photoshop, but I think you'll get the idea of what I'm proposing here for an adjustment mechanism.

I took the mast off my OHP built my own, all the parts I would need to build this mech could be swiped off that mast.
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Old 26th September 2003, 05:22 PM   #7
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Maybe you could just fix the frame with bolts and nuts in it's position once you've set it . I mean DIY projectors usually are not moved quite often.

Btw. If you tilt the projector 20 degrees the center of the picture will be (tan theta ) * (pj's distance from the screen)

For an example if the distance is 250 cm the center of the image will be tan 20 degrees * 250 cm = 91 cm higher than the pj lens. In my pj the lens is 60 cm (+adj) from the floor, so the projected image's center will be about 151 cm from the floor.

Anyway it might be better to build some stand on which to put the chairs like in real movie theatres.
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Old 27th September 2003, 12:50 PM   #8
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I got my keystone correction working. I tilted the projector and the LCD+fresnel. Also the pj lens had to be tilted to be parallel with the screen to get the whole picture sharp. The projector is now on the floor quite close to the screen (~2 meters), picture is reasonable size, no problems, no trapezoid picture!
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Old 30th September 2003, 09:37 AM   #9
hassler is offline hassler  Australia
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This is what I planned to do (I'm hoping the picture will upload properly)

Is this what you did Mhelin?

The angle of inclination to the floor, is that the same angle that the 2nd fresnel has to be tilted to??
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Old 30th September 2003, 11:41 AM   #10
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hassler, you tilt the 2nd fresnel wrong direction. Also you should keep the pj lens where it is but angle it parallel to screen.

Btw, I use this kind of setup, though I may split the fresnel some day. I have small problems with light, the upper part of screen is dimmer and there's also some light leak there (upper part of screen) which makes black grayish.
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