'new' keystone adjusting idea - Page 2 - diyAudio
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Old 30th September 2003, 05:27 PM   #11
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Default neato!

yeah splitting the fresnel should fix your "low light at the top" problem i believe..I am still using a regular ol' OHP with a standard projection panel..i've got a 60" screen and i'm pretty happy with the results. I only have a couple problems (leaky light for one) that I know I can fix but this is the only one that is still troubling me...so with a standard OHP could I just add one more lens between the mirror and the screen that will tilt up and down to fix the problem? if so i'm guessing it would need to be bigger than the lens at the top of the projector....hmmmm
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Old 1st October 2003, 04:54 AM   #12
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No, just tilt the panel on OHP and adjust the mirror on pj lens, that should do it.

Actually I'm going to tilt the LCD too because I wouldn't like to split the fresnel. It's doesn't have to be adjustable, the angle doesn't matter as far as it's enough.
Actually I've tilted the pj by "a" dagrees: tan a = 8 cm / 60 cm = 0.133.. <=> a = 7.6 degrees. Not much, but that's still enough for me. DVD's anyway use only the middle part of the screen and the picture is high enough. With these OHP lenses and stuff the pj must be close to the screen anyway. Yeah, light leakage is still a problem for me too.
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Old 1st October 2003, 08:58 PM   #13
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Ok, I tried tilting the TFT and it did work, but the screen now is wider in upper side, kind of trapezoid effect though the picture is straigth. The pj just shows more of the desktop (in PC). That can be easily corrected by using screen with black edges (that also improves contrast).

The picture was dark in upper part of screen because the mirror was not properly positioned, not in correct 45 degrees angle and a little bit too far from the pj lens (I had this problem already before trying to adjust the keystone). It would be nice if the mirror had not to be used. I can't see any way to mirror BenQ's picture (I know it's might be possible, many TFT's have that kind of option).
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Old 3rd October 2003, 07:10 PM   #14
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Default UPDATE

Ok, I finally split the fresnel tonight, and the picture with keystone correction (2ND fresnel tilted) is now PERFECT. Don't even bother to try the other ways (tilting panel or tilting unsplit fresnel+panel) they are useless.
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Old 30th October 2003, 06:26 PM   #15
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well guys i got my infocus lp220 today and i found out it has a keystone for those who are interested it has 2 frensels, the front one tilts for the keystone about 10deg maybe 15 at most but at full keystone at such the small degrees it makes one hell of a big impact on the projected image, so for those who are going to get into the keystone thing i think the tilting of the top frensel is the way to go, a simple cam is suficient for this, for those who are interested ill draw a pic of how the one in the infocus is set up if you guys want it.

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Old 16th February 2004, 01:30 PM   #16
mathias is offline mathias  Sweden
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I lend this tread for awhile. When I installed my commercialprojector I understood that there is a big difference how the picture is projected in a commercialprojector and a diy-projector. Until now people have solved this with keystonecorrection.
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Old 16th February 2004, 01:33 PM   #17
mathias is offline mathias  Sweden
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I think this solution is more like the commercial offset solution with this you donīt need any keystonecorrection at all.
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Old 16th February 2004, 09:55 PM   #18
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Ok, I want to ceiling mount my projector. I want to mount the PJ 10' from the screen, giving me an 8' by 6' screen. I am trying to figure out what angle to mount the PJ from the ceiling, and therefore the front fresnel, as the angles are congruent. Anyway, i have a couple questions and any help would be appreciated.
First of all, is it just as simple as tilting the top front fresnel (top) and leaving it at that, or do I also have to tilt the projection triplet? I have read through all of these posts, but it is not clear. Second, Anyone know the correct angle to mount the PJ from the ceiling in order to get a 8x6 screen that is 1 foot from the ceiling (therefore the center of the screen is 4 feet away from the ceiling)? Also, since i am mounting on the ceiling, will the fresnel be tilted perpendicular to the ceiling? I hope these question make some sense. It is kinda hard for me to know the best way to word these types fo things. I guess it would be easiest if someone would whip up a drawing. I appreciate any help.
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Old 16th February 2004, 11:44 PM   #19
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is it possible to leave everything in the setup completeluy straight forward except the projection lens which you could tilt a little bit
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Old 16th February 2004, 11:46 PM   #20
Dwiel is offline Dwiel  United States
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I just tried it on my PJ, and got it to work :-) I will probobly be working on making a more permenent way of tilting the fresnel, but it works for now. One thing you need to watch out for is your fresnel size. I didnt see anyone mention that if you rotate your fresnel 30deg, you will only be able to consider its width to be 86.6% of whatever it was initially. To find the percentage for your given rotation, just take the cosine of your angle. Luckily, the width of my fresnel is large enough to compinsate for this reduction in 'usable' width, and so this works for me. Also note that you will probobly not be rotating your fresnel 30deg... you never know... Just take the cosine of the # of degrees you rotate. I was able to get everything to work by simply rotating the fresnel. The projection didnt seem to need rotation.

Im not sure about the relationship between the angle between your PJ and screen and the angle between your LCD and fresnel.

Hope I've helped
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