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Discussion Starter · #1 ·
I'm very confused about keystoning. I'm strongly considering purchasing a MP-38T, but I'm not sure if I can mount in a way that I can avoid using the digital keystone correction.

Here's a link to drawing of my planned media room. The ceiling will be about 7' 4". Ideally, I'd like to sit about 11' from a roughly 70" wide 4:3 screen.


So, I understand that the projector needs to be roughly 11' from the screen based on its throw ratio. But, I have no idea where the projector needs to be relative to the ceiling to avoid any need for digital keystone correction.


Can someone enlighten me?


Thanks.


/jab


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No offense but I am confused by your confusion. http://www.avsforum.com/ubb/biggrin.gif


First your room layout does not make any difference on if you will have a keystone issue assuming that you are keeping the projector on center to the screen. If you were thinking of off center placement then you might have problems but your picture shows it on center to the screen. Where keystone typically becomes an issue is when someone has a tall ceiling and they flush mount the projector and angle it down to a lower screen height.


While I haven't used this projector but I am going to assume it is like most other projectors. You are going to purchase some type of ceiling mount and attach the projector. This will place the lens a few inches from your ceiling. Assuming your projector is level, when you turn your projector the image should be close the same height as the lens. I think some projectors may drop the image a few inches but I am not sure. My top of the image coming out of my lens is about 6 inches from the ceiling and my screen starts at ~ 6 inches from the ceiling.


If you are mounting a screen wall, just wait until you have the projector installed. Get the projector setup throwing correctly against the wall where the screen is going. Mark the areas on the wall where the screen should go and just mount it in the same place and you should have no problems with keystone.


Hope this helps. If not can you help me understand better what your concern is?


Regards,


Brian
 

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One more thing you should know if you are installing something like a Stewart screen wall, they stick out a few inches. If I recall correctly it was something like 3 inches. This might make a difference on where you place the projector when aligning the mount bracket to a joist and making sure you have left appropriate slack in your zoom to fine tuning the throw.


Regards,



Brian
 

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Actually, this projector does drop the image (when floor mounted level) a few inches, which means it will raise the image a few inches when ceiling mounted.


I looked in my manual and for a 100" diagonal 4:3 screen, with projector 11'-8" away from screen, the image raise will be 2.9", or about 3". So you need to determine where the top of your screen is relative to the ceiling, and your distance to the center of the lens will be that distance plus 3" for level mount.


You do NOT want to use the digital keystone on this projector, it adds distortion. Mount the projector level as described above and the image will be perfect.


Dan Houck


Email me if you need further details about this.


Dan
 

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I agree with Dan,

NEVER use digital-keystone correction for HomeTheater setups. Change the height of the PJ, or change the height of the screen any way you can, but please put down your remote and step away from the keystone knob!


Optical-keystone adjustment is OK.


However, I think the list of projectors that have optical-keystone (the lens moves up and down) is very short.


Hey, while I'm thinking of it, does anybody have the phone number for the HomeTheater Police?

 

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Discussion Starter · #6 ·
Quote:
btmoore wrote

No offense but I am confused by your confusion.
A sure sign that I need your help. I don't even know enough to ask the right questions. http://www.avsforum.com/ubb/smile.gif

Quote:
HTbuff wrote

Hey, while I'm thinking of it, does anybody have the phone number for the HomeTheater Police?
LOL!


OK.


If I understand this correctly now, I ceiling mount the projector. The mount probably adds about 4" of drop. The projector has about 3" of rise. Therefore, the picture would be about 1" below my 88" ceiling. With a 60" wide 4:3 screen (reconsidering the 70"), the center of the picture would be about 64" above the floor.


That sounds high to me. Shouldn't the center of the picture be closer to 36" off the floor?


Even with the extension mounting pole, I'm not going to get the center below 40", and at that point the projector would only be 55" off the floor! That's going to make it very hard to hush and very easy to run into.


If I try to floor mount it, it needs to sit on top of the sofa. <sigh>


Am I simply very confused?


The 73" Mitsubishi RPTV is beginning to look better, even though it isn't a great 4:3 solution...


/jab


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Quote:
Originally posted by JAB:


If I try to floor mount it, it needs to sit on top of the sofa. <sigh>


Am I simply very confused?


/jab

I think you might want to visit somewhere or someone who has a projector setup to help you get a better contextual understanding on how seating, mounting, projector height and screen height all come together. I don't know where you live but you might post a request asking if someone in your area can show you their setup. Once you understand it better you feel better and it beats the hell out of having a big black box in the room. FYI IMO in a ~8FT high room you will want that screen as high as you can get it.


Best of luck.


Regards,


Brian
 

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Discussion Starter · #8 ·
I've always found understanding the theory to be crucial to understanding what you see in someone's room and what you should expect to see in your own room. I did drop by a local A/V store. They had a Runco. It was mounted at the rear wall and projecting onto a much larger screen than what I'll have. Different projector. Different room. Different screen size. I'm not quite sure what I'm supposed to take away from that experience that will apply to my room.


Are my calculations wrong?


If not, what I hear you saying is that I'm wrong about wanting to have the center of the picture closer to eye level.


I'll make an effort to see some more installations, but I'd still like to understand how to predict what needs to happen in my room.


Thanks.


/jab


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Discussion Starter · #9 ·
I've borrowed a Plus U2-1130 from work to play with tonight. Here's what I've learned:


1. No way I'm getting a smaller screen. http://www.avsforum.com/ubb/smile.gif


2. A sheet makes a surprisingly good screen. http://www.avsforum.com/ubb/smile.gif


3. 64" is too high for the center of the picture. It makes my neck hurt. http://www.avsforum.com/ubb/frown.gif


4. At 2x screen width, I'm very sensitive to rainbows. Rainbows everywhere. No DLP for me. http://www.avsforum.com/ubb/frown.gif


I'd like to feel confident that I can reasonably install the XP21N in my room.


/jab



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JAB,


My XP21 is ceiling mounted with the lens almost exactly level with the top of the screen (200 inch diagonal, 4x3, with the projector 27ft from screen, about 9.5 ft from floor). The projector is almost exactly horizontal therefore I assume the manufacturer expects this to be a 'normal' situation. Of course, adjustment must be made for keystone in this case, and I found the keystone adjustment through the 'screen' menu works perfectly. I am not aware of any distortion of picture.


Regards,


John Holmes
 

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Discussion Starter · #12 ·
I'm not sure I understand. If the projector is level, why would you need to use the keystone correction?


/jab


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According to the manual of the XP21N, for a 60" x 80" screen, the centerline of the lens should be 2.9 inches up from the bottom of the screen. I assume if you ceiling mount and flip the image, the centerline of the lens should be 2.9 inches down from the top of the screen. For a 60" diagonal (48w x 36h), it would be 1.8" (.029*60).
 

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Dear JAB,


Re my response above, my XP21 is ceiling mounted as I said, almost horizontal and almost level with the top of the screen. Nevertheless, the keystone distortion was definitely apparent and I had to make adjustments for it. My "of course" statement was of course incorrect. The need for keystone correction in this context must depend on the alignment of the LCD and projector optics. If the LCDs and optics are partly tilted to achieve the picture offset from centre this will demand some keystone correction. If the LCDs are exactly vertical but offset from the centre path, in theory there should be no keystone distortion. The fact is that I had to use some keystone correction from the original projector settings.
 
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