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I can't get a perfect rectangle from my projector

Discussion in 'Projectors, Screens & Video Processors' started by phfjones, Oct 2, 2004.

  1. phfjones

    phfjones
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    Dear all,

    I may be missing some basic point here, but I have just set up my Digital Projection iVision projector with an Eight foot 16:9 screen, and I have found that the image the projector throws is not a perfect rectangle, and cannot get it to fit my 92" x 52" area. I thought this had something to do with keystoning, but this moves the whole image up down or sideways, but does not 'stretch' the image to fit (I assume this is the only way I can do this?)


    The difference is that the right hand part of the screen fills the screen, but on the left edge of the screen I have a gap of about one cm both at the top and the bottom of the picture. How do I get the picture to a perfect rectangle?

    Thanks in advance.............

    Paul
     
  2. Tempest

    Tempest
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    Twist the projector a little to the left

    When I got projector I spent ages, with a extendable rule, twisting the projector left right and up/down till all distances were the same, also having to rotate the projector to make sure the image is square.

    Just twist left right to get the height the same both sides
    twist up down to get the width the same along to top and bottom edge
    and rotate it to get the image square with the wall.

    Take a while
     
  3. KraGorn

    KraGorn
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    Paul, are you saying the centre of the left edge is flush with the edge of the screen, while the top and bottom aren't, making the whole edge sort of an arc rather than straight line .. like the pincushion you get on a CRT? But just the left edge, the right is perfectly straight, yes?
     
  4. Tempest

    Tempest
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    Ahhh, no, if that's what you are getting then my instructions wil not work.

    If you are getting CURVED edges to your screen rather than straight lines then it sounds like something must be curved inside the projector (or poss a lens issue)
    I was just talking about everything being straight, but just the sizes (lenghts) being wrong which you correct by moving the projector.
    Not something like pincusion.
     
  5. andy9

    andy9
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    i cant get a spot on rectangle, have to make do with a little spill onto the black border, you can only see it if you know its there, one of them things.

    i think its because the screen might not be totally square to the projector, or the projector needs to be lowered more. i dont want to use keystroking as i've read it degrades picture quality.
     
  6. KraGorn

    KraGorn
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    If the screen wasn't square-on to the projector you'd expect to see opposing sides distorted slightly, which is what keystone adjustment corrects and as you say that's not a good idea. The only thing I know of that can cause a curved edge from the projector is the optics.

    Try something. Assuming your projector is table-mounted go into the menu and set it for ceiling mount. Re-adjust the image. If it's a problem with the lens the flaw will move to the right edge, if it's the screen it'll stay on the left.
     
  7. phfjones

    phfjones
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    Thanks Guys,

    Yes, the centre of the left edge is fine but the top and the bottom of the left edge is short by about one cm compared to the right side which looks fine top, centre and bottom. It is ceiling mounted, and unfortunately cannot be moved now it is in place.

    I look forward to hearing from you,

    Cheers

    Paul
     
  8. LV426

    LV426
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    Let me check: Your problem is, that at one side of the image:
    a) it is less TALL than at the other side

    OR

    b) one vertical edge is curved so that it's wider near the centre than at the top and bottom?


    a) is caused by you having positioned the projector incorretly in relation to the screen. The projector lens needs to be aligned with the dead centre of the screen, widthways. If not, the image will be trapezoid and you can't correct it.

    b) is most likely caused by the screen material being curved.
     
  9. phfjones

    phfjones
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    Thanks Nigel,


    I think I am in scenario 'a'. I can move it about two inches without having to reposition the projector. I'll try this and see how I get on.

    Thanks to all, a great help.

    Paul
     
  10. KraGorn

    KraGorn
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    Oh well, I was only trying to help isolate the problem.

    In any case I think I misunderstood your description, I was reading it that the top edge was 1cm in from the LEFT EDGE and ditto at the bottom, whereas your reply to Nigel seems to say it's 1cm from the TOP, and vice-versa from the bottom.

    In that case then Nigel, surely that's what keystone adjustment is for, to correct the trapezoid into a rectangle? Albeit with a 'hit' to picture quality.
     
  11. cliocarl

    cliocarl
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    keystone would correct a picture like the blue one but what happens if you get a pic like the red one?????????????? :confused:
     

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  12. LV426

    LV426
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    I'm not sure about the model in question. Some PJs have keystone correction in one direction only (vertical) which would correct the blue shape, but not the red one. Others have keystone correction in both planes in which case you can correct the red one. And some have a lens shift feature which corrects the issue optically (this is a better technique).


    phfjones: if you can't move the projector, how about moving the screen? If the left edge is smaller than the right, it means that it is nearer to the projector. If you get a tape measure and measure the distance from the left edge of the screen to the lens, and then the right - you could correct the problem by angling the screen so that these two measures are equal - move the left back, or the right forwards.
     
  13. phire42

    phire42
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    When the projectected image is like the one that is Red on the right side, it's because the lens is not PERFECTLY parallel to the screen. The projector is either twisted a little to the left or a little to the right. If this is a projector sitting on a table, it's easy to fix, you twist the projector until it's PERFECTLY rectangle and then MOVE (without twisting) the projector left or right until the perfect rectangle is on the screen.

    The problem comes when you have the projector ceiling mounted. Because if you twist the projector until it's a perfect rectangle often the rectangle is part way off the screen. (You twisted the projector in the first place in order to move the rectangle ONTO the screen) So now that the perfect rectangle is half on the screen and half the screen you only have two options for resolving that problem.

    1. If your projector has lens shift use the lens shift to move the perfect rectangle onto the screen (without twisting the projector)

    2. If your projector does not have lens shift then your only option is to move your mounting hard ware. This really sucks, but it either that or twist your projector so it puts the the image back on the screen but is no longer perfectly parallel and you will have the red image again.

    Often times when people have this problem they are using the same mounting hardware that they used to hang a different projector before and it didn't have this problem... Well that is because projector manufacturers put the lens at different places on the front of the projector. Some put the lens all the way to the edge, some put it 1 inch away from the edge, some put the lens dead center. That 3-5 inch change in the location of the lens is enough to put the perfectly parallel lens far enough over that the rectangle is no longer on the screen. When this happens people often twist the projector to compensate and end up with this problem. It sucks but you have to take down the projector. Take down the projector mount. Find out where the optimum location is for this projector and re-mount it at the new location. Then the lens will be perfectly parallel, the rectangle will be on the screen and you will have a perfectly rectangle projection (until you get a different projector with the lens in a different location... then you may have to do it all again.)

    GOOD LUCK!
     
  14. KelvinS1965

    KelvinS1965
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    I suspect the OP might have upgraded by now since this thread is 9 years old. :smashin: Projectors that provide optical lens shift (as opposed to digital keystone) can be much easier to line up to a screen, though they still require twisting, etc to align it up.
     

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