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focus error correction on curved screens

Discussion in 'Projectors, Screens & Video Processors' started by Vilya, Jul 11, 2005.

  1. Vilya

    Vilya
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    Hi,

    when projecting onto a curved screen, even with projectors especially designed for the purpose like a Barco 909, the (flat) focal plane of the projector and the curvature of the screen don't align, causing blurring.

    I could not find anything on the net, but is there a hardware solution to this problem? Does a video projector exist whose lens system can correct or at least curve the focal plane of the projector?

    AFAIK the only system capable of this is the Curvulon, a lens used in the 60ies for special curved screen theatres. Or am I mistaken?

    http://www.in70mm.com/newsletter/2004/68/l...er_curvulon.htm

    Best regards,

    Vilya
     
  2. Gary Lightfoot

    Gary Lightfoot
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    Hi Vilya,

    I posted a thread on Torus screens which came from avsforum in the US - is there anything in there that's helpful for you at all?

    Gary.
     
  3. Rich-1000

    Rich-1000
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    Hi Vilya

    I assume you are interested in projecting a 35mm print onto this curved screen. The 35mm curvulon lens used for Dimension-150 and other deeply curved screens for 35mm presentation used a combination of lenses to create a very deep field of focus to correct your problem.

    One lens acted as the primary lens. A second lens basically doubled the focal length of the first lens. Yet another lens then reduces the focal length of the image back to the correct size, but with a great depth of focus.

    The best results come from an image projected 0 degrees off center -- in other words directly projecting "level" at the center of the screen. No keystone issues being added.

    I do not remember if the theatre where I saw this in use was using a reverse anamorphic (such as a drive-in theatre would use for an extremely long throw). I do have photos that I took of the set-up and will try to locate them to see if the scope lens was traditional or a reverse anamorphic.

    I hope this helps you some.

    Rich
     
  4. Rich-1000

    Rich-1000
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    One additional thought that might help. Your light should not be too bright. The perfect projection light is about 15 - 16 f.l. at center screen with the projector running without any film in it. A little less is ok. If you have too much brightness, however, your image can appear to be out of focus even if all adjustments are "right on."

    Thanks

    Rich
     
  5. Mad Mr H

    Mad Mr H
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    There were optional lenses on the 909 (cine9, 1209 etc)

    HFQ904 and another I seem to remember......

    These were designed for curved screens
     

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