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Height from ceiling calculation… arrrggghhhh!!!

Discussion in 'Projectors, Screens & Video Processors' started by t1grm, Dec 21, 2004.

  1. t1grm

    t1grm
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    I’m tying myself up in knots trying to do some calculations for projector height from ceiling for a Screenplay 4805.

    I’ve pretty much sussed the throw distance I need for the width of screen I’m planning on buying (190 cm) using the web based tools but the height is a bit trickier.

    I’m using the method described by theritz here:

    http://www.avforums.com/forums/showthread.php?t=80073&highlight=projector+height+calculation

    Using this I get the following figures (all in cm):

    Constants:

    190 = Viewable width of screen i.e. max picture width
    107 = Picture height (based on 16:9)
    304 = Room height
    100 = Floor to eyelevel (when seated on sofa :smoke: )
    47 = Projector lens height from floor when on coffee table

    So optimal bottom of picture to floor based on eyelevel being 33% the height of the picture is 64cm (100 – (107/3)).

    This leaves the difference between lens height from floor and base of picture from floor being 17cm (64 – 47).

    Next top of picture from floor is 171cm (64 + 107) which makes top of picture from ceiling 133cm (304 – 171).

    So adding the difference between lens height and top of picture this gives me a theoretical projector height from ceiling of 150 cm (133 + 17) :eek: !!!

    This would be right in my line of view, not to mention most inconvenient for day to day living, so can’t be right.

    I think where I’m going wrong is assuming the 47cm from floor to projector lens. I won’t know this until I get the projector home and set it up. Obviously I don’t want to go and buy a projector if the ceiling to projector height is going to be 1.5m! :nono:

    Am I going about it the right way or is there another way to do this? :rolleyes:
     
  2. SimonInd

    SimonInd
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    I think you're missing the fact that the projector will be upside down when ceiling mounted so the drop from the ceiling will be 133cm - 17cm = 116cm. This should be out of your way, however if you can vary the height of the screen and get an adjustable ceiling mount you might find that raising them both a little is preferable - I have my 8ft wide screen about 80 - 90cm from the floor and sit about 11ft back on a Lay-z-boy sofa.

    Cheers
    Simon
     
  3. t1grm

    t1grm
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    Thanks for the info.

    Can I ask what height the PJ is from the ceiling in your set up?
     
  4. Tempest

    Tempest
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    Get some steps of something, a few books on top, whatever.

    Put the projector on the pile (very temporary - just for a test) and run it.

    You can then see on the opposite wall the image position.

    Then you can work out how much higher/lower you need to have the projector (from it's trial height) for final mounting.

    Much easier to try it for real than calculate.
     
  5. t1grm

    t1grm
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    Problem is I’d like to get an estimate before I buy. If we’re talking 1m then that’s seriously going to impact the usability of the room for non Cinema related activity seeing as the estimated throw puts it right in the middle of the room. I don’t want a dirty great pylon sticking out a meter from the ceiling all the time.

    Another possibility is the NEC HT410 with its lens shift feature. I think this would allow me to get it nearer the ceiling.
     
  6. Gary Lightfoot

    Gary Lightfoot
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    The NEC HT1000 or HT1100 have quite a big offset and would probably sit very tight to your ceiling. Might be worth a look. My old Ht1000 was about 3.5ins from the ceiling and the 7ft wide image was 19ins from the (7ft) ceiling. Some pics on my website if you're interested.

    I've just got an Optoma H77 and that has lens shift, but it needs to be over 30cms from the ceiling to fit onto the same screen, so it's more obtrusive than the NEC was. It's not a problem as it's a dedicated room, but I prefer the pj to be closer to the ceiling.

    Gary.
     
  7. SimonInd

    SimonInd
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    My BenQ PE8700 is on a Vogels fixed ceiling mount, that I'd recommend - looks nice and esy to install, about 10 inches below the ceiling. Because of the way it projects it is closer to the ceiling than my AE100 was for the same screen. The top of the screen is probably 18 inches from the ceiling ( 8'6" ) from memory.

    I would imagine that if you can accomodate the throw, then given the variety of screens and mounts out there, you should be able to cover all bases. Remember if you want to have the projector a bit higher, you can always raise the screen a little. You'll not know for sure until you get it home, but they do say 'necessity is the mother of invention' so I'm sure a solution can be worked out....

    Good luck

    Simon
     
  8. PJTX100

    PJTX100
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    Though my room is a dedicated AV/study room I had the same concerns, especially as I planned to attach it to an exposed beam. I wanted the drop to be as small as possible. Inspired by Gary L's pics (thanks Gary :thumbsup: ) I made an MDF bracket, the main difference was I fashioned a sliding clamp out of a few pieces of floorboard. The advantages of this are a) 1" drop b) rock solid. The disadvantages are a) rock solid b) hence no adjustment ;) I think I lucked out however because I only had to adjust it twice before everything was perfectly square, and with the horizontal/vertical lens shift on the TX100 the rest was easy. I suspect not many people have a bracket with zero adjustment on it however!
    Before going this route I bid 80 quid for a Vogels on eBay but it didn't meet the reserve price. I had a look at the metal / screw / twisty thumbwheel setups but they looked a bit flimsy for the price. Anyway the MDF cost me a fiver, and I only used a quarter of it, hence it may be worth a try...
    ...PJ
     
  9. t1grm

    t1grm
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    Thanks for the feedback folks. I think I’ll plump for the Screenplay 4805 and mount it tight to the ceiling then adjust the screen height to suit. I can always put the sofa on some telephone directories. :D
     
  10. PJTX100

    PJTX100
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    Now *that* is an interesting idea. :laugh:
    I'd better get started on this wrapping mularky. :rolleyes:
    ...PJ
     
  11. Jack's Dad

    Jack's Dad
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    I've just purchased a 4805 and had the same issue about ceiling mounting mine. You've probably seen this already so forgive me if I'm stating the obvious, but the offset from the centre of the screen is 27% of the screen height.
    I'm using a Vogels universal mount which gives about 4 and half inches between top of PJ and ceiling, and the image is 15 and a half inches from the ceiling. This is with a 71 inch width screen.
    By the way, the image quality is fantastic with my Pioneer 575 via component.
     
  12. Jack's Dad

    Jack's Dad
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    Oops - meant to say offset is from centre of lense NOT screen. doh!
     

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