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Vertical Refresh Rates

Discussion in 'Projectors, Screens & Video Processors' started by Leon Rees, Apr 21, 2003.

  1. Leon Rees

    Leon Rees
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    There's been some discussion here in the past about how increasing vertical refresh can improve image quality, particuarly slow left to rigtht pans...

    I'm wondering, with something like a Barco 808s, would a 72Hz or 75Hz vertical refresh put additional strain on the projector?

    I would have thought that there's is no free lunch with increased vertical refresh rates. Does projector have to work harder? Is the focus as sharp at higher refresh rates?

    Thanks for any help!

    Leon
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Leon,

    The projector has to work harder. Dependant on the phosphor used in tubes you might also find that the green hasn't had a chance to "calm down" before being zapped again. This could result in blooming and lack of detail (softening of image). Roland will be able to advise on optimum for an 808 I'd think.

    Using 72Hz refresh requires 3:3 reconstruction of film source material. There are few devices that can do this. Rock, Original Leeza, Terranex, Interpolator, probably HTPC can do it. Immersive Assimilator is supposed to as should HD-Leeza when they come out.

    If the intentio jnis to use higher refresh rates then it's adviseable to do complete focus and set up at the rate you are going to end up using. IE start from scratch again.

    Gordon
     
  3. Roland @ B4

    Roland @ B4
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    Leon
    Most people move to the higher refresh rates to remove the flicker that is associated with 50 and 60 hz. More of that in a mo.

    To answer your question the projector will deal with it easily, it will get slightly warmer because its working a bit more.
    In pure resolution terms an 808s with good tubes working on a 16x9 screen should be able to reproduce 720 lines any more and they will overlap and the image will start to become softer.

    The standard phospors in an 808s will more than cope with 75hz

    The smothing of the image and juddering during panning shots tends to be more associated with how a device can deal with recognising film or video.
    Most of the material we watch in our home cinemas will be film based. It's been covered before but a quick recap. Film is shot at 24 frames per second (fps)which is comparativly slow. Often panning shots have judder just from this slow shooting speed. However for those who are new to the "film to video" conversions a quick recap.
    Video in the UK works at 50hz (based on our mains supply) in the states its 60hz.
    To copy film in the UK is relativly easy you just speed it up to 25 fps and then shoot each frame twice. ( uk films don't last as long)
    Speeding up to 30fps would just make the vioces higher and the action a bit strange so for (NTSC, region1, the states) they had to do something clever. the still shoot each frame of film twice but every third frame is shot again. This gets the running times correct but is a nightmare for scallers and the like to work out. Most of the BIG scallers that Gordon mentioned have the processing power to cope withgoing to the fater refresh rates and they work best in multiples of what ever conversion system was used. Therefore 75hz for the UK (multiple of 25 fps)and 72hz for the States mutilpe of 24 fps.

    So the projector will cope with it it a question of weather your scaller can?
     
  4. fatrich

    fatrich
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    Roland
    Just out of curiosity i run every thing through my computer as you know and are uding the Holo3dgraph card, for NTSC i run it at 59.94Htz (which is what Immersive recomend) and when i get sky fitted in the cinema room next week end i will try it @ 50Htz, my question is what will happen if i bang the pj up to 100Htz (will it blow up?) whilst watching pal and why do they recomend 59.94 Htz in stead of the normal 72 for NTSC.

    P.S. can you please e-mail me with some dates so u can visit Halifax and recalibrate my BG808.

    cheers

    richard
     
  5. Jeff

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    Richard,

    NTSC is 59.94Hz, 72Hz (or 71.928Hz) works well with NTSC films because the 3:2 sequence gets reconstructed as 3:3, so smoother. 72Hz however doesn't appear to be an easy thing to do since very few scalers support it. The standard H3D software can't do 72Hz properly, DScaler can do it due to the Judder terminator software.
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Reason for not doing 72Hz for NTSC is that video sourced NTSC is recorded at 30fields per second. It's designed for playback at 60Hz (59.94) 72Hz is ideal for FIlmsource as Jeff says.

    Gordon
     
  7. fatrich

    fatrich
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    Jeff,Gorgon
    thanks, what about the 100Htz pal question though?

    cheers

    rich
     
  8. Roland @ B4

    Roland @ B4
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    Of the few times I've seen it, the image becomes too stable and just doesn't look right not soft exactly just not film.
    I suspect the phosphor is not gettting sufficient time to decay.

    The projector will do it ok so give it a go an let us know what you think.
     
  9. fatrich

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    Just to let you know i tried 100htz and your right it didnt look right out of 50htz and 75 htz the 75htz looks the better, but still having more fiddeling and fine tuning to do yet.
    Roland can you please email when its cinvinient to come and recalibrate my bg808

    ta

    richard
     

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