TV Projector mounting-I dont understand this

Discussion in 'Archived Threads 2001-2004' started by Lawera_P, Dec 13, 2001.

  1. Lawera_P

    Lawera_P Auditioning

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    I just purchased a Infocus 350 and plan to mount it using a ceiling bracket (which is made by Infocus). Here is the thing that I dont understand. I am mounting this projector on the ceiling and logic tells me I must angle the projector down at some angle to center it on my screen. I talked to Infocus tech support and find out that the lense centerline is not suppose to project on the screen at an angle as it will distort the picture. HUH???? If I mount the projector on the ceiling I gotta angle the projector, Besides, I dont want to sit the projector on a table at a 5 foot elevation and have people walking in front of the image everytime someone gets up. I am sure there are those that have to angle the projector...does it really distort the image to the point that it is noticable??????

    thanks in advance....
     
  2. Sean M

    Sean M Stunt Coordinator

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    How high is the ceiling in relation to the screen? For most projectors, you align the lens with the bottom, or top in this case, of the screen squarely and the image will fire at the correct angle to fill the screen properly. Angling the projector will introduce keystone distortion, which you wish to avoid at all costs. Have you fired up this projector yet to see just how the picture comes out of the lens?
     
  3. Garry C

    Garry C Auditioning

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    The tech is correct, it is better if you don't point the projector at an angle. If you do, you will have to use the keystone correction to make a rectangular image.
    It's best if you position the projector straight at the wall (the bottom of the projector is parallel with the floor/ceiling). The projector has to be hung lower than the top edge of the screen but higher than the centre of the screen. The formulae about positioning the unit should be in the user manual.
    I have the NEC VT540. At about 20 feet, it projects about 4" below the projector and 70" above the projector. The projector is hung from the ceiling upside-down so the projector is above my sofa and I am looking straight at the image.
    I hope this makes sense and helps. Good luck!
    I checked out the infocus user guide. It's not very helpful. Here is the link to the NEC user guide. Look on page 16 for a good illustration.
    NEC VT540 User Manual
     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    The projector manufacturers realise that most of the machines are going to positioned with the base of the machine more or less level with the bottom (or top if ceiling mounted) of the screen. They also know that the projector will probably sit flat on a table top or projection stand. The projectors are accordingly designed such that the lens is offset from the central perpendicular axis of the imaging chip. Think of it as taking the lens and physically shifting it up without tilting it. This allows the projector to create a proper image with the machine level with the screen base and without a tilt. Once tilt is involved, keystone distortion appears and you need further compensations.
     
  5. JasG

    JasG Auditioning

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    The following link has an Excel spreadsheet that will allow you to calculate the vertical position for mounting your projector. It will depend on your screen size & projection distance.
    IMHO, it is very important to avoid using the digital keystone feature of any projector. I use my pj for a computer monitor and you would not believe the image degradation (fuzzy text) caused by even 1% keystone adjustment!
    http://www.infocus.com/service/lp340_350/spec_imgch.asp
     

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