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Using a mirror?

Discussion in 'Projectors, Screens & Video Processors' started by fozziebear39, Apr 8, 2003.

  1. fozziebear39

    fozziebear39
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    Hi

    Has anyone got experience of mounting a projector vertically and using a mirror to get a bigger picture if you have a long throw projector in a short room? Sort of like those old RPTV.

    Is it possible?

    Thanks
    DF
    :suicide:
     
  2. Anders_UK

    Anders_UK
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    Sure it is possible, and very easy to do. Just be careful in chosing the correct mounting positions as most projectors (other than CRT's) use arc lamps and these go pop if you put them in the wrong orientation.

    Use graph paper (or CAD in my case) and layout your system, put in the required screen size and the position of the projector to give you the said size. Then draw in the light rays back to the projector, both horizontal and vertical. At this point the light path/layout won't fit in the room, so place a fold line at the position you want and then re-position the projector so that it works. handy hint if you are drawing by hand is to use a real mirror placed over the sketched fold line to see where the projector will end up.

    The mirror type to choose are of the FRONT silvered variety as these have a reflectivity of around 98% and do not have all the errors that everyday mirrors have. DO NOT USE household mirrors you can buy in a DIY shop.

    Other than that it is a piece of cake.
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Yes it's possible. Roland did a similar trick with a 1209 (crt) at a show once. This is how rear projection displays work incidentally (well some anyway). The mirror will change colouromitry of the image slightly but you may not notice this...unless you use smoked glass mirror:laugh:

    Gordon
    Edited to point out Anders beat me to it......
     
  4. Anders_UK

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    Yeah rear projection displays need a long throw distance to reduce the incident angles hitting the rear of the screeen (unless using a fresnel lens) so to reduce the system footprint you fold the light path up using 2-3 folds. Nice and compact systems.

    I think paradigm has a automatic program on its website for folding projectors, if not it will give info on mirrors for ya.
     
  5. Chris Frost

    Chris Frost
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    Fozzie,
    just be careful about pointing your projector skyward. It will screw up the way the heat dissipates through the body of the machine. Very few LCD/DLP projectors are designed to cope with this. It would be a shame if you cooked yours to death.:eek:

    Try a double mirror rig instead. The layout is like a letter Z. Projector fires at towards screen, image bounces of a small mirror, then back onto a larger mirror and then to the screen. Other benefits are bigger picture for shorter throw distance and less of a problem with keystone correction. Look at Paradigm for a guide, many of their LCD rigs use this principle.

    Regards
     
  6. fozziebear39

    fozziebear39
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    Thanks for the inputs. Yes I am considering the Z way (not that serious yet lol but would like the projector to sit as it was meant to). Seen the Paradigm site, amazing stuff. I use Autocad so can work out the angles etc.

    Would build it into a chimney breast so all hidden away. May chicken out and just build a hush box into the chimney breast and get an extra 1'6" throw.

    I could just build my cinema extension but that it taking the expense of this hobby to extremes lol

    Fozzie.
     
  7. MrSafety

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    Fozzie

    This is a really neat idea which has immediately caught my eye. How big would the mirror need to be? Couldn't you put the PJ on a side wall and project at right angles into the room and use the mirror to turn it back onto the screen? Then you wouldn't need to sit your PJ vertically you could just place it on a table or whatever.

    I am about to have the reverse problem - I have a long throw PJ which needs to project onto an end wall but the end wall is too small to take the full image size even on "no zoom". I had wanted to mount my PJ on the back wall but now I need to either consider a ceiling mount or have it in the middle of the floor somewhere. I don't suppose there is way of using mirrors to get the image size smaller is there ?!?
     
  8. Anders_UK

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    Nope there isn't any way of reducing image size with mirrors. They just give you the option of increasing the throw distance to a screen without massively increasing the footprint.

    Try talk to the projector manufacturer and see if they have another lens option..in your case a longer throw, most do but just don't publicise the fact. Failing that try Buhl and buy a add-on lens that will have the same effect.
     
  9. John_N

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    I'm currently building an experimental hush box based around using a mirror.

    This way, the projector fires "sideways" ie - parallel to the wall and then the mirror folds the image through 90 degrees to exit the hush box at it's half way point and hit the screen. This way, the hot air and noise exhausted out of the front of the projector carries on into the other end of the husbox to be absorbed and extracted through a duct.

    J
     
  10. Chris Frost

    Chris Frost
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    Not quite correct. Manufacturers don't make lenses just to have them sit on a shelf because nobody knows they're available. That isn't good business practise. If a manufacturers range includes optional lenses then these may be designed for specific models. Don't assume that they'll fit your particular projector. Check compatibility before ordering.

    Fozzie, if there is a longer lens available for your projector you should find details on the projector spec sheet, instruction book or their website.

    Many of the Buhl lenses are replacement rather than additional "clip-on" style. Replacing the lens will affect warranty. They are also manufactured to order so you have to be absolutely certain that you've made the right decision. Finally there is the cost.

    Regards
     
  11. MrSafety

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    Still thinking about this option...

    Wouldn't a mirror reverse the image so that left-hand became right-hand? Wouldn't you need two mirrors so that the image wasn't inverted?
     
  12. fozziebear39

    fozziebear39
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    Your projector may have options on menu to flip image horizontal and/or vertical so should be able to use one mirror, not tried it yet, but if you want to look at the mirrors...


    I have this link from some kind member before:

    http://www.vacuumcoatings.co.uk/Autocue-FSmirrors.html
     

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