BenQ HT3550 Screen Adjustment Help - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 21 Old 09-07-2019, 08:54 PM - Thread Starter
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BenQ HT3550 Screen Adjustment Help

Finally was able to mount the projector to basement studs (3 stacked side by side) with BenQ CM00G3 mount.

First off, the screen is mounted properly and is level:



Initial adjustment of the mount yielded this:



Note the image above shows the left side and bottom edge to be level. The top and right side is skewed.

After adjusting zoom to fill the 120" screen and lense shift, I can now only get the left side and top to be level and straight:



Note from the picture up above, the right side is slanted (like before) and now the bottom is skewed. It would seem that the test pattern is not exactly rectangular and the right side is taller than the left, hence this effect. But this is probably an optical illusion.

Is there a way to fix this issue? I have tried keystone adjustments, which didn't help. This unit only has vertical. I think it needs a horizontal keystone adjustment but this is not possible? Is there a way to adjust the picture to be exactly rectangular? No matter how much physical adjusting i do on the mount, i cannot get the picture to be correct. Am I missing something?

Is my unit defective or am i missing something obvious?

Thanks for any input.
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post #2 of 21 Old 09-08-2019, 01:16 AM
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Using a level is not enough. The projector is not perpendicular to the screen. Walls and ceilings are never plum and true to the accuracy required to get a perfectly square picture. Never use digital keystone as it will no longer have one to one pixel mapping and degrades the picture. Try pushing or pulling the corners of the screen closer or farther away from the projector and shim to correct the errors. The use of a black velvet border to absorb the minor imperfections in alignment is what most of us do as it is very difficult to get it exact.

Edit: Looks like you have a zero edge screen so adjusting is almost impossible. Using a projector without horizontal lens shift compounds the problem as you must move the projector left or right by fractions of an inch to get it exactly centered and perpendicular to the screen. If your mount doesn't have horizontal adjustment maybe you can move the screen a few inches left or right. This is why I never understood the appeal of a zero edge screen.
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post #3 of 21 Old 09-08-2019, 07:56 AM
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Quote:
Originally Posted by Anubus12 View Post
Finally was able to mount the projector to basement studs (3 stacked side by side) with BenQ CM00G3 mount.

First off, the screen is mounted properly and is level:



Initial adjustment of the mount yielded this:



Note the image above shows the left side and bottom edge to be level. The top and right side is skewed.

After adjusting zoom to fill the 120" screen and lense shift, I can now only get the left side and top to be level and straight:



Note from the picture up above, the right side is slanted (like before) and now the bottom is skewed. It would seem that the test pattern is not exactly rectangular and the right side is taller than the left, hence this effect. But this is probably an optical illusion.

Is there a way to fix this issue? I have tried keystone adjustments, which didn't help. This unit only has vertical. I think it needs a horizontal keystone adjustment but this is not possible? Is there a way to adjust the picture to be exactly rectangular? No matter how much physical adjusting i do on the mount, i cannot get the picture to be correct. Am I missing something?

Is my unit defective or am i missing something obvious?


Thanks for any input.

Yes, what you're missing is the screen is not plumb. No amount of projector mount adjustment will correct it. You will have to correct the way the screen is hung on the wall.

You can have the screen level, horizontal and vertical, and be out of plumb.

Walls are seldom smooth and plumb; plumb is the vertical alignment. It's not uncommon to be out 1/4"-1/2" over a 4' span or even more.

How is your screen mounted to the wall? French cleat type bracket, keyhole screw, etc.? What you have is one or more of the mounting points attached to the wall, is deeper or further away from the screen frame attachment point than the other(s) causing the screen frame to bend or warp. What you're seeing is the test pattern following the contour of the bend.

If you can get a long level or straight edge and check the horizontal portion of the frame, especially the part of the frame that is holding the screen to the wall, you'll find the bend or warp. You can correct this by shimming or sometimes as simple as backing the screws out so as to not stress or bend the screens frame.
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post #4 of 21 Old 09-08-2019, 08:06 AM - Thread Starter
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Quote:
Originally Posted by rekbones View Post
Using a level is not enough. The projector is not perpendicular to the screen. Walls and ceilings are never plum and true to the accuracy required to get a perfectly square picture. Never use digital keystone as it will no longer have one to one pixel mapping and degrades the picture. Try pushing or pulling the corners of the screen closer or farther away from the projector and shim to correct the errors. The use of a black velvet border to absorb the minor imperfections in alignment is what most of us do as it is very difficult to get it exact.

Edit: Looks like you have a zero edge screen so adjusting is almost impossible. Using a projector without horizontal lens shift compounds the problem as you must move the projector left or right by fractions of an inch to get it exactly centered and perpendicular to the screen. If your mount doesn't have horizontal adjustment maybe you can move the screen a few inches left or right. This is why I never understood the appeal of a zero edge screen.
@rekbones Thank you so much for the response.

TBH, when looking for a screen, I didn't really consider it thoroughly. I just thought it looked "cleaner" with a zero edge.

So first, you don't think the projector is defective? I ask because others have mentioned the edges of their units were skewed as well. I am hoping this is not the case because I really don't want to spend months waiting for a replacement.

Second, can you please explain a bit more about using black velvet border? I presume that is not an option for me because of the zero edge.

Third, you think that the projector is not squared to the screen completely. From the pictures above, does that mean the left side is square and the right side is not? Meaning the projector is square but the screen is not. If so, how does sliding the screen left and right help? Shims might be the only option?

Lastly, in regards to shims. Any tips on shimming and keeping them in position? Since the screen is just hung on hooks, there isnt a good way to keep them in place.

Sorry for all the questions and thank you for the help!
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post #5 of 21 Old 09-08-2019, 11:14 AM
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From looking at your pictures there is more then one issue. If any part of the screen is closer to the projector you will get a smaller picture and farther away will be bigger. First make certain all digital keystone is at zero before you adjust anything. Try and get a square picture with the image zoomed smaller by rotating the projector left or right assuming the projector is level and the screen is plumb. If you can't then the screen is not flat in relation to the projector as this is where shimming is required.. If you can get it square and the image is not centered you need to move the projector or the screen to center it as you can not rotate the projector once it is square. If the projector is not level or the screen is not plumb the image will be wider on the top or bottom depending on the direction it is out. If the projector is not perpendicular ie rotated some the image will be taller on one side or the other.
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post #6 of 21 Old 09-08-2019, 01:27 PM
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With a zero edge screen it is still possible to have boarder masking. Work as hard as you can to the information above and get the image as close as you can to fit without using keystone correction as advised above. When you get it as good as you can you can over-zoom your screen just a slight amount and then if the wall behind your screen is black or better yet black velvet it will drink up the over-spill and the image will float in space. If you can’t do that you can get a black velvet tape and put a boarder around the screen stuck to the wall.
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post #7 of 21 Old 09-11-2019, 06:09 PM
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Put a shim under the bottom right corner of the screen, just tape it to the wall temporarily with some painter's tape to see if that helps.
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post #8 of 21 Old 11-07-2019, 08:42 AM - Thread Starter
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Quote:
Originally Posted by barryecohen View Post
Put a shim under the bottom right corner of the screen, just tape it to the wall temporarily with some painter's tape to see if that helps.
Thank you for the reply. Sorry for the late response. Per your suggestion, I tried to add the shim and it definitely helped the image. However, it "bends the screen" a bit too much. I am afraid it would damage the screen since the one corner is pulled off the wall a bit too much making it warped. There is no other way?

I am shocked at how much off square to the projector the wall really is.

Thanks!
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post #9 of 21 Old 11-07-2019, 08:50 AM - Thread Starter
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Originally Posted by bud16415 View Post
With a zero edge screen it is still possible to have boarder masking. Work as hard as you can to the information above and get the image as close as you can to fit without using keystone correction as advised above. When you get it as good as you can you can over-zoom your screen just a slight amount and then if the wall behind your screen is black or better yet black velvet it will drink up the over-spill and the image will float in space. If you can’t do that you can get a black velvet tape and put a boarder around the screen stuck to the wall.
Thanks for the reply!

I am trying to square the screen as much as possible. It's not perfect but getting closer with shimming. However I am not certain it is a good permanent solution as I am worried about warping the screen.

In regards to your suggestion, I was thinking about how best to do that. Black velvet would be best but more troublesome to hang. I am guessing I would need to hang behind the screen?

As for painting, that was my next thought. Please take a look at my picture of my humble HT. The color of the wall is mustard (i didn't choose it LOL). The right side has curtains. Would it be best to paint that wall a flat black? Would that accomplish the same thing as black velvet in regards to overscan and such (although not as good)? Would that help with contrast as well? Or what is a better color?

Also where is best to best to get black velvet for this application, if i have to go that route.

Thanks for any input.
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post #10 of 21 Old 11-07-2019, 09:02 AM
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Originally Posted by Anubus12 View Post
Thanks for the reply!

I am trying to square the screen as much as possible. It's not perfect but getting closer with shimming. However I am not certain it is a good permanent solution as I am worried about warping the screen.

In regards to your suggestion, I was thinking about how best to do that. Black velvet would be best but more troublesome to hang. I am guessing I would need to hang behind the screen?

As for painting, that was my next thought. Please take a look at my picture of my humble HT. The color of the wall is mustard (i didn't choose it LOL). The right side has curtains. Would it be best to paint that wall a flat black? Would that accomplish the same thing as black velvet in regards to overscan and such (although not as good)? Would that help with contrast as well? Or what is a better color?

Also where is best to best to get black velvet for this application, if i have to go that route.

Thanks for any input.
IMHO if painting the wall flat black is an option I would do it. doing that would hide any detail on the wall and would blend in with your bank of black speakers and equipment.

The only drawback to flat black is it will smudge easy with handprints and such, but in your case it doesn’t look like that would be a problem.

If down the road you want velvet just at the edge they sell self stick velvet tape I believe.
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post #11 of 21 Old 11-07-2019, 10:32 AM
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Originally Posted by Anubus12 View Post
Thank you for the reply. Sorry for the late response. Per your suggestion, I tried to add the shim and it definitely helped the image. However, it "bends the screen" a bit too much. I am afraid it would damage the screen since the one corner is pulled off the wall a bit too much making it warped. There is no other way?

I am shocked at how much off square to the projector the wall really is.

Thanks!
Not sure how the screen is mounted to the wall, but shimming a corner shouldn't warp the screen, unless the other 3 corners are tightly secured to the wall(?)

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post #12 of 21 Old 11-08-2019, 09:55 AM - Thread Starter
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Not sure how the screen is mounted to the wall, but shimming a corner shouldn't warp the screen, unless the other 3 corners are tightly secured to the wall(?)
The screen is mounted flat against wall with the brackets in the attachment. 4 brackets, 4 points. Lower right corner sees to be the most affected, meaning i have to shim it about 2-3 inches away from the wall to make it line up. Doing this doesn't seem to be the right thing to do and isn't a good permanent solution, with one corner pull away from the all that much. Just something seems way off, but it's not readily apparent.
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IMHO if painting the wall flat black is an option I would do it. doing that would hide any detail on the wall and would blend in with your bank of black speakers and equipment.

The only drawback to flat black is it will smudge easy with handprints and such, but in your case it doesn’t look like that would be a problem.

If down the road you want velvet just at the edge they sell self stick velvet tape I believe.

Since I am impatient, I did as you suggested last night LOL. Black certainly hides the imperfections in the wall and does enhance the visibility of the screen as it stands out more. I didn't play with any adjustments of the projector yet, but it does seem to mask the upper right corner image spill onto the wall. Question is, even after painting the wall, is it necessary to add velvet tape (3-4 inches) around the edges as well? If so, how would that help further?
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post #14 of 21 Old 11-08-2019, 10:20 AM
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The screen is mounted flat against wall with the brackets in the attachment. 4 brackets, 4 points. Lower right corner sees to be the most affected, meaning i have to shim it about 2-3 inches away from the wall to make it line up. Doing this doesn't seem to be the right thing to do and isn't a good permanent solution, with one corner pull away from the all that much. Just something seems way off, but it's not readily apparent.

So, looking at that diagram you have the screen pinned tight to the wall, and the wall isn't square, so pinning the screen to the wall on four corners is probably the problem, and warping the screen. Remove both bottom mounts, just let the screen hang from the top and see where you are.

P.S. In your original post, in your first attachment you hold your level to the edge of the screen. Flip the level 90 degrees on the long edge, and see how level/plumb the wall is. I bet it's off.

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Originally Posted by barryecohen View Post
So, looking at that diagram you have the screen pinned tight to the wall, and the wall isn't square, so pinning the screen to the wall on four corners is probably the problem, and warping the screen. Remove both bottom mounts, just let the screen hang from the top and see where you are.

P.S. In your original post, in your first attachment you hold your level to the edge of the screen. Flip the level 90 degrees on the long edge, and see how level/plumb the wall is. I bet it's off.
Thanks for the reply. I will unhook the bottom two and see where the screen "hangs". If that works, should i just leave it like that? feel a bit insecure with only 2 points and screen is held in place by gravity.

BTW, great job on your HT room.
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Thanks for the reply. I will unhook the bottom two and see where the screen "hangs". If that works, should i just leave it like that? feel a bit insecure with only 2 points and screen is held in place by gravity.
Well, those bottom two brackets don't really support the screen, they just hold the bottom against the wall and prevent the screen from being lifted up off the top brackets. If the screen hangs nicely using just the two top brackets, and you're worried someone will unhook it accidentally, just add a stop of some type at the top of the screen to prevent it from being lifted off the brackets.

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BTW, great job on your HT room.
Thanks!

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Since I am impatient, I did as you suggested last night LOL. Black certainly hides the imperfections in the wall and does enhance the visibility of the screen as it stands out more. I didn't play with any adjustments of the projector yet, but it does seem to mask the upper right corner image spill onto the wall. Question is, even after painting the wall, is it necessary to add velvet tape (3-4 inches) around the edges as well? If so, how would that help further?
Great job. If it were mine I would call it done and just enjoy.
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post #18 of 21 Old 11-09-2019, 09:07 AM - Thread Starter
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Great job. If it were mine I would call it done and just enjoy.
I think I am going to do just that. Thanks for the help!
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Well, those bottom two brackets don't really support the screen, they just hold the bottom against the wall and prevent the screen from being lifted up off the top brackets. If the screen hangs nicely using just the two top brackets, and you're worried someone will unhook it accidentally, just add a stop of some type at the top of the screen to prevent it from being lifted off the brackets.
I removed the two lower brackets but, unfortunately, didn't help. Shims are the the only way to go. Just need to find a better way to permanently do that. One thing I haven't tried yet is sliding the screen left or right. I can't too much because then it wont be centered on the wall.
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post #20 of 21 Old 11-12-2019, 12:51 PM
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One thing I haven't tried yet is sliding the screen left or right. I can't too much because then it wont be centered on the wall.
Maybe I missed it, but... Is the projector's lens centered to the screen?

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post #21 of 21 Old 11-12-2019, 02:30 PM
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Not sure how I missed this thread...

In the initial photos, the lens is CLEARLY not centered left/right to the screen.

To adjust the left/right position you want the top and bottom of the test pattern to be perfectly aligned with the top/bottom of the screen.

Being off by a couple of inches results in the top/bottom lines not being parallel as you can see in the photo. The top line is dropping a bit to the left.

To correct this, the projector (since it has no left/right lens shift) must physically be moved towards the side which is smaller. Only by about an inch or so.

Check again to see if the top/bottom edges are parallel. Repeat this process until the lens is perfectly centered left/right.

Now, you adjust the height.

The 3550 should offer a bit of up/down lens shift. Similar to the HT2050A. It's rated at 10% which means that the lens should be able to have about 5" of range on a 100" diagonal image. A bit more for 120" diagonal.

In the past, this has meant that the lens could be about 3" to 8" above the top of the screen (when ceiling mounted) and the target was always about 5" above the top of the screen. So, if your screen is 15" from the top of the ceiling, then the center of the lens should be 10" from the top of the ceiling. This is, generally speaking, ideal for this particular model.

Now, you are on center and your lens is 5" above the top of the screen. But, the lines are not parallel to each other.

In your photo, they clearly bow outwards towards the bottom. This means that the projector is pointed downward slightly.

Tilt the projector up, then use lens shift to shift the image downward until it is on screen.

Check again and see if the lines are parallel.

Repeat this process until the lines are parallel to each other. Always tilt the projector in the direction that is smaller. Then lens shift back until the image is on screen.

Obviously, if you need to physically move a projector left or right after you've already bolted it into the ceiling and your projector mount puts the center of the lens 10" above the top of the screen when you only are allowed to go 8" above the top, you are going to have some placement issues. Then you get into keystone correction, the drop in image quality that goes along with that, and a lot of personal choices. In my view, you shall not use keystone correction. You shall put a projector where it belongs. Proper projector placement is critical to best image quality and I didn't just drop $1,000+ on an image that I'm willing to compromise image quality on. But, that's my choice and doesn't have to be yours.

There are plenty of quality mounts which offer very precise height flexibility.
There are not many mounts with good left/right adjustability.
I ALWAYS take my projector to the top of a ladder, upside down, plug it in, and run a test pattern on screen to ensure I have proper left/right placement ahead of mounting it to the ceiling. If I'm within about an inch, I typically can tweak it close with the mount to get it perfect.

I wish you luck if you continue further down this path.

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