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Ceiling Mounted PJ & Keystone - should I worry?

Discussion in 'Projectors, Screens & Video Processors' started by richardS, Sep 22, 2004.

  1. richardS

    richardS
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    Okedokey....

    Just got the kit below to go in a purpose built viewing room.

    - HT300plus (second hand)
    - Draper Premiere 7ft tab tensioned screen (second hand)
    - Cabling/Power was installed into the ceiling for the projector, in roughly the right place for throw ratio
    - Screen will be fixed to same ceilling


    Reading through this forum (I should have done this a while back as the Pandora's box has well and trully been opened) - I began to get worried...

    I haven't yet bought a ceiling mount but there seems to be a lot of threads about keystone correction and how it affects image quality. Because the room is also a kids playroom, I cannot put the projector anywhere safe except the ceiling (and even that won't deal with flying objects).

    So...my questions are;

    1. I'm I going to affect the picture if I mount to the ceiling?
    2. If so Is there a mount that I should buy to minimise this? Is flush mounting out of the question?
    3. The room is 6.40M from screen to rear wall and 2.6M floor to ceiling - with seating on the rear wall. Should I rethink the position of the projector (i have no idea if the HT300Plus can deal well with the extra distance bearing in mind the screen size will stay the same) and mount on rear wall?

    Any thoughts would be greatly appreciated...
     
  2. KraGorn

    KraGorn
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    The feature you want to look for is 'vertical lens shift'. I don't know about the HT300+, but both my Z2 and the Z200 have this and it allows the image to be moved up or down the screen up to 1/2 its' height .. the Z2 also had horizontal too.

    What this means in practice is that at the extreme you can have the projector's lens in line with the top of the screen and use the lens shift to centre the image. You don't ideally want to use the extremes of the shift, doing that reduces light output and can, if the optics are less than perfect, introduce slight image defocussing at the opposite edge, ie. in your case the bottom edge.

    You are absolutely right, keystone adjustment is a PQ killer to be avoided unless absolutely necessary, so check if the HT has this feature and your problems will be greatly reduced given your limitations with respect to having to have it mounted high up.
     
  3. richardS

    richardS
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    KraGorn thanks for that reply -

    I have been looking into the spec sheet but cannot find anything that mentiones "vertical lens shift". All the info refers to Keystone correction - "The projector is so versatile that it can be placed on a bookshelf or installed in the ceiling corner opposite to the screen. "....

    I quote;

    "Optical keystone adjustment: +/-8°
    Digital keystone adjustment: +/-13° vertical, +/-10° horizontal
    Throw ratio 1.8 – 2.4:1
    Picture size:50-300 inches diagonal.
    Aspect ratio: 4:3, 16:9, anamorphic, letter box plus 3 custom-user adjustments, panoramic and pixel to pixel"

    The next thing to find out is how much of a drop I will need on the ceiling bracket to minimise keystoning and at the same time avoiding heads and flying toys - as well as the wrath of the other half - "What in God's name is that hanging from the ceiling!!"....."but honey...It gives a better picture...."
     
  4. KraGorn

    KraGorn
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    I've not come across "Optical keystone" but that sounds okay, though 8 degrees is a bit limited. The reason 'digital' adjustment can badly affect PQ is because it distorts the image by eliminating and replicating pixels rather than just bending light.

    If all else fails then you'll have to use it. The HT300+ is not exactly an entry-level machine so its' digital keystone may be better quality than on lower-end projectors.
     

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