BenQ HT3550 Screen Adjustment Help - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 09-07-2019, 07:54 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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Last edited by Anubus12; 09-07-2019 at 07:58 PM.
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post #2 of 7 Old 09-08-2019, 12:16 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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Last edited by rekbones; 09-08-2019 at 12:32 AM.
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post #3 of 7 Old 09-08-2019, 06:56 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 7 Old 09-08-2019, 07:06 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 7 Old 09-08-2019, 10:14 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 7 Old 09-08-2019, 12:27 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 7 Old 09-11-2019, 05:09 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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