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gain ? some info please..

Discussion in 'Projectors, Screens & Video Processors' started by the klang, Apr 23, 2005.

  1. the klang

    the klang
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    sorry to ask old questions but...
    im ordering a pt ae700 next week and im having problems finding the right screen for it .can anyone recommend a level of gain or at least point me in the right direction as to how you understand what gain is .
    any help would be great !
     
  2. MikeK

    MikeK
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    It depends on how big you want the screen, what the audience viewing angle is, the level of light control in the room, how the projector is mounted, the light output power of the projector, and your own personal preference as to how bright you like the image.... amongst other things :).

    There is no magic one-fits-all, unfortunately!
    What type you should get depends on all these factors, amongst others (such as price, type of screen (ie foldaways, fixed etc))

    Gain itself, is the amount of light a screen reflects back relative to a standard white screen (there is an ANSI standard for this I think), which has a gain of 1.0.
    This type of screen reflects light in as uniform a fashion as possible (ie diffused - it does not direct the reflected light in any particular direction) and has a wide viewing angle.

    No screen can reflect back more light than is actually shone onto it - that's the first thing to understand about positive gain screens (ie screen with a gain of more than 1.0)

    What positive gain screens do is to start to direct the reflection of the light, similar to a reflector in a torch. The higher the gain, the more directional the reflected light becomes. The screen will appear brighter when you are in front of it, but will dim off as you move to the side. The higher the gain, the more noticable the effect, and the narrower the ideal viewing angle becomes.
    One thing you need to consider with a high gain screen, is the angle of the projector in relation to the screen, and it's position relative to the screen.
    With a standard high gain screen, if you project from below the screen (ie coffee table), the majority of the light will be refected upwards towards the ceiling, not back towards the viewer, essentially defeating the purpose of the high gain. Use a ceiling mounted projector, and you're OK - as it's above the screen, the majority of the light will be reflected downwards, more towards the viewers.
    For coffee table mounting, you need to investigate retro-reflective screens, which, within limits, tend to reflect the light back towards the direction it actually came from!
    There are some variations to these norms though, such as special purpose designs etc, so you'd have to look at each on it's merits.

    What negative gain screens do (screens with a gain of less than 1.0), is absorb some of the light shone onto them - ie they don't reflect back all the light which is shone onto them. They are usually grey in colour (as grey is neutral) - the shade of grey dictating the level of gain.
    However, it's possible to have postive gain grey screens too - what these do is absorb some of the light, but are more directional reflecting back the rest!
    The actual grey colour of the screen gives deeper blacks, which is always something of an issue with projectors to one degree or another.
     
  3. the klang

    the klang
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    mikek,thanks for that!
    the room is small and dark and the pj puts out 1,000 ansi and the size of the screen will work out about 2meters across and just over 1meter down ish .the pj will be mounted dead opposit the screen in the wall about 4 meters away.
    cheers again.
     

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