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Discussion Starter · #1 ·
I searched but could not find a good answer re: balancing projector tilt and lens shift.


I just purchased an AX-200U. Currently, my throw distance is 14 feet, but have at least 10' behind the projector. I have not run the cables yet, because I might need to move the projector further back(?). One reason I bought the AX-200u was for versatility for positioning.


My room has 14' ceilings, and the longest (affordable, Adtec) extension I could find drops my projector 35" off the ceiling, or 133" above the floor. The top of my screen is 81" off the floor. So the difference is 52", which is more than allowable 25% of the my 120" 16:9 screen (59" x 109"). So I guess I'll need to tilt the projector. The manual allows for a 30 degree tilt, but I'm worried about keystone, etc.


I have a few questions:


1. Is the configuration too poor? Should I just hunt for a longer extension rod? Or do you think I should continue and adjust the projector to make it work? (running the wires is going to be a beast, so I don't want to do it twice). Am I degrading my picture significantly?


2. How should I "balance" the lens shift and tilt? In other words, I don't want to crank the joystick as far down as possible, right?


3. Would it help to move the projector back (i.e., reduce the angle between the lens and the center of screen)?


4. I read that adjusting the keystone affects the scaling which degrades the picture quality. Think it would be significant in my case?


5. Any other tips to keep my picture quality high?


Thanks so much.
 

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The vertical lens shift on the ax200 is 250% of screen height not 25%. You should have no problem.


"In addition, the AX200U has manual horizontal and vertical lens shift. When the lens is in its neutral position, the centerline of the lens intersects the image just above its geometric center. From this position the vertical lens shift will let you reposition the image up or down within a total range of 2.5 picture heights."

http://www.projectorcentral.com/pana..._projector.htm
 

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Discussion Starter · #3 ·
Hmmm, well I just re-checked the manual, and indeed it is not 25% (that's for horizontal shift). The manual says 63%:


"You can place the projector where the projector lens is up to 63% vertically off-center from the screen and the adjust the image position with the lens shift feature."


So that would be 59" times 0.63 = 37 inches, which is still less than 52", the smallest shift that my current set-up allows.


Wonder where PC got 250%?
 

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Discussion Starter · #5 ·
I could, but then I'd be violating the rule of:


Eye level at bottom one-third of screen.


And the overall aesthetic of the current screen position is nice.


I guess I'd rather add to the mount's extension arm as opposed to changing the screen position.
 

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Quote:
Originally Posted by oysterhead /forum/post/15565723


I could, but then I'd be violating the rule of:


Eye level at bottom one-third of screen.

I can't figure that one out. I see it posted from time to time but I have never seen a movie theatre where that rule applies. In fact, in a THX certified theater you are supposed to sit 2/3rds of the way back to get the best distance from the screen and at that point, which I always try to get and I like the best, my eyes are at the 1/3rd of the screen from the top not the bottom.



If you can, put up a longer extension.
 

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I also think you should try to find a longer extension pole. Worst case scenario you could probably find a metalworker who could fab one for you fairly inexpensively.


I've never understood that 'rule' either. Though I have to admit I adhere to it in my theater as well.
 

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Quote:
Originally Posted by ionyou /forum/post/15587762


I adhere to it as well, because my neck likes it. Not because someone tod me to.

You definitely don't want the bottom of the screen above your eyeline!
 

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oysterhead -- Several points to start with. First, at 14' your AX200 is too close to the screen at 14'. Your PJ should be roughly 16', or more from the screen (again, see http://www.projectorcentral.com/Pana...ulator-pro.htm ). For a 120" screen, the throw distance range for the AX200 is 12' 1" to 24' 6" (front of lens to screen), so you have lots of zoom range to play with, moving the PJ back further is going to be better.


Second, your screen is too low. The eyes at 1/3 of the way up the screen is OK, but this is not eye height, but where your eyes fall on the screen when sitting in a relaxed position (with your backbone straight). No one sits "bolt upright" in a chair, etc. In my case, the bottom of my 106" screen (92" x 52") is at the same height as my eyes (about 33" off the floor), but I sit in a semi-reclined position, so with my back straight, my eyes fall naturally at about 1/3 of the way up the screen. The bottom of your screen is only 22" off the floor (way too low for most seating). You can easily raise your screen by 10" to 12" and, with the proper seating, have your eyes fall at the "correct(?)" height (with your back straight).


Third, you do want to stay away from using the maximum vertical lens shift. At the end of the lens shift range: (1) you will lose all horizontal lens shift capability, and (2) you will start to get chromatic aberration and other lens quality effects at the extreme ends of the shift range (= 47" from the center of your screen, in your case).


Third, you don't ever want to "tilt" the PJ. Using the "keystone" adjustment results in a reduction of resolution (and you have only 720p to start with) and adds artifacts to the image. The more tilt, the worse these effects are. An ordinary 2" diameter pipe (which can be painted, to make it less obvious) is a low cost way to drop the ceiling mount lower, as needed.


As the other members have said, get an additional extension (a piece of pipe is the usual, but not the only, choice).


Putting all of this information into a package, I get the following:

1.) Screen bottom (viewable area) = 34" off the floor (physical screen bottom will be ~32" off the floor).

2.) The screen center will then be 59/2 + 34 = 63.5" off the floor. Adding about 40" of vertical lens shift, puts the center of the AX200 lens at about 103.5" off the floor.

3.) If the distance from the center of the lens to the bottom of the AX200 is about 2.5" (I'm guessing, but that is typical), then your PJ bottom should be about 106" off the floor (= ~ 8' 9").

4.) For a 14' ceiling, that means that your mount + post has to be about 5' 3" or so, give or take 3". That comes to just around 63", bottom (remember it's upside down, so the "bottom" is up) of PJ to the ceiling. Therefore, you would need around an additional 30" (2.5') of pipe to drop the PJ to the right height. Putting the AX200 much higher, will start to get into the "recommended keep-out range". As I said, these dimensions are all +/- 3".


I hope I've walked you through the factors, calculations, and dimensions correctly. You have to fine tune them for your exact seating position (which will determine the screen height). Remember the screen height is relative to where your eyes actually are looking at in your relaxed seating position, and not your physical eye height.

PS -- If your room is 24' deep (screen to back wall), then you could actually mount the AX200 on a shelf on the back wall. The shelf will have to be about 18" to 2' deep, since you need room for the cables and air flow. That would put the lens to screen at about 22' to 22' 6" from the screen (which is within the zoom range for a 120" screen). That would completely eliminate the lens shift problem.
 

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Discussion Starter · #11 ·
Wow, CT, that's the post that every noob dreams about. Thanks so much.


A few responses...


1) Projector too far: I knew that I didn't want to be at the shortest throw, but also knew that the closer the brighter. So I guessed 14'. Wish I'd seen that calculator! I'll probably move the mount backwards to 16' instead of 14'.


2) Screen too low: sitting only slightly reclined, with back straight, my eyes hit 1/3 up the screen. I'm 6'5". But I just ordered new chairs (Berkline). Once I'm rolling with new leather, I'll re-evaluate the screen height with your recommendation.


3) Yep, the vertical shift is too much. I ordered another mount. I'm gonna steal a couple of the poles, and then put the mount on eBay, minus two poles. For people who don't need much extension, they can get a mount at bargain price. This was much cheaper than purchasing a whole new mount. (p.s. the shelf on a back wall is a good idea, but my room is too big. Plus, then I'd have to channel through the drywall to get the cords in the ceiling and run to the closet with my equipment).


4) Yep, I can see the keystone right now, and can't fully correct it. But the additional extension poles will solve that!


Again, THANKS SO MUCH. posts like these are what makes this forum awesome.
 

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Discussion Starter · #12 ·
After looking at the calculator, I see that it's simply recommending the average of the max and min distance.


I had always heard that you want the projector to be close, but not at min throw. This way, you get max brightness without compromising contrast.


But maybe this old rule of thumb was wrong. Or maybe average is the easiest number to recommend.


EDIT: WOOPS, NEVERMIND it's not the average, which is over 18'. It recommends less than the average.
 

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These days I always mount as close as possible for the screen size I desire.


No real set best practice on this anymore.



Your really set on this projo? It does seem a one chip DLP with their massive fixed offset would be perfect here.
 
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