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cannot get a rectangular picture

Discussion in 'Projectors, Screens & Video Processors' started by Adam M, Dec 17, 2001.

  1. Adam M

    Adam M
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    Hi guys,

    I am at my wits end.

    The bottom of the image will not sit parallel to the screen. The top isnt even parallel. It is closer than teh bottom but what can I do.

    The projector is a dls 8 mounted on the ceiling bracket. I suppose it is entirely possible the room isnt parallel (infact probable).

    I have eliminated the tombstone effect, but the image is decidedly rhombuslike ( dont know the correct adjective).

    I am getting sick of this set up and dont know what to do.

    someone suggested buyign the new cheaper sony which is electroncally sorted in advance. I cant imagine the picture will be as good for the price difference.

    Any thoughts or suggestions?
     
  2. Chris Frost

    Chris Frost
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    The lens of the projector should point at the centre of the width of the screen. Yours is off to one side. You also have the projector twisted in relation to the level of the screen, which is why you can't get the image aligned.

    The Davis (and many other single lens projectors) put the lens to one side of the projector body. DIYers forget to account for this when installing the bracket. This makes the image distorted in the way you describe.

    Measure how much offset there is between the centre of the lens and the centre of the bracket when attached to the projector. Assuming your original mounting holes line up with the centre of the screen, use the offset distance to drill new holes and then remount the bracket.

    CRT projectors can be mounted slightly off centre, but single lens projectors are very unforgiving of slight errors in the mounting bracket.

    Features like Keystone and the new "side shot" feature can help, but they do so at the expense of picture quality because of the extra processing required to distort the image. Where possible, you should have the projector mounted so that no keystone is required. This will give the best image quality.

    Regards
     
  3. Gary Lightfoot

    Gary Lightfoot
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    Hi Adam,

    I had a few probs getting my DLS8 straight too.

    I found that the pj needed moving to the right a little more so that I could get it lined up with the screen better. The right side of the projected image was bigger than the left because the pj was twisted to the right. It always seemed straight at the top, but the bottom right was always a little lower in the r/h corner.

    Having it too far off center will mean that one side of the screen will be bigger than the other.

    Having it too high will give keystoning (tombstoning), but you say that's OK (both sides are parallel I take it?).

    If the wall the screen is on is not square with the pj, you may have to move the screen out on one side or top or bottom.

    Has your ceiling mount got positioning adjustments for up down and roll?

    It sounds like the pj isn't central or square to the screen.

    HTH

    Gary.
     
  4. Adam M

    Adam M
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    appreciate teh reply, but already made sure the lens was down the centre line of the screen.

    Key stone was an issue as the upside down projector wanted to start the image way below the ceiling where it should start and finish almost at the floor.
     
  5. Chris Frost

    Chris Frost
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    Adam,
    OK, you say that the left and right sides of the image are parallel to the screen, and your projector is mounted centrally to the screen.

    Have you measured from each end of the screen case to the centre of the lens?

    These two distances should be the same, if not then your projector isn't at 90 degrees to the screen surface even though it is mounted centrally. The solution, either move the bracket or alter the screen so that the measurements tally. If this fails (very unlikely) then you must have some optical problem with the projector. Has it ever been dropped?

    Regards
     
  6. leon

    leon
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    is it a pull down screen or fixed ??
    i had a problem with this on a owl screen and the bar got a little bent over the years ,it made my picture about and 1 inch to wide on one side .
     
  7. Roland @ B4

    Roland @ B4
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    I'm with Chris the projector is not at right angles to the screen.

    Try using cotton thread to measure the distance it doesn't stretch.

    Another tip if you have access to a laser pointer. Tape a mirror absoloutly Squarely over the lens of your projector. Take the laser pointer to the very corner of the screen material (not the screen box) and point it at the centre of the lens (yes I know, some one covered it with a mirror) or where it would be. If your projector is spot on the beam will hit the other corner of the screen.

    I disagree with a CRT not needing to be as accurate. 1 or 2% of the screen width out will make a huge differnce to the stress on the convergence and geometry settings. which will make it over heat and drift or fail.
     

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