RPTV screen order?

Discussion in 'Archived Threads 2001-2004' started by Dan Driscoll, Dec 13, 2001.

  1. Dan Driscoll

    Dan Driscoll Supporting Actor

    Joined:
    Aug 1, 2000
    Messages:
    937
    Likes Received:
    2
    Trophy Points:
    0
    I just restacked the screens on my Pioneer SD-533 using Michael TLV's instructions to get started (thanks Michael). But I am curious as to whether there is a reason for the order the screens are arranged in.
    From the inside out, the screens on my 533 are fresnel, lenticular, contrast (glare). When restacking screens to eliminate glare, typically the contrast screen is moved to the back of the stack, so the new order becomes contrast, fresnel, lenticular.
    But there are quite a few people who advocated completely removing the contrast screen, contending that putting it on the inside of the stack simply increases reflections inside the cabinet, causing halos, poor blacks and other undesirable effects. But the contrast screen provides most of the strength and rigidity for the stack and removing it increases the potential for bowing.
    This made me curious. As a compromise, could the contrast screen be placed between the fresnel and lenticular screens? That would make the screen order, from the inside out, fresnel, contrast, lenticular. The potential problem here is that I have heard that the fresnel and lenticular screens are designed to work together as a unit and the putting the contrast screen between them would degrade picture quality.
    If this is the case, then complete removal of the contrast screen would seem to be the better alternative.
    Any comments would be appreciated.
     
  2. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

    Joined:
    Mar 16, 2000
    Messages:
    2,909
    Likes Received:
    1
    Trophy Points:
    0
    Location:
    Calgary, Alberta
    Real Name:
    Michael Chen
    Greetings

    Did you notice that the fresnel lens is just as reflective as the protective screen?

    As long as there is a mirror in there, you will always have internal reflections.

    Placing the stack as you described may result in a focus problem since the L+F are to work in direct contact with each other. You will also likely end up with a light dispersion issues as well.

    But it cannot hurt to try. You can always undo it.

    Regards
     
  3. Dan Driscoll

    Dan Driscoll Supporting Actor

    Joined:
    Aug 1, 2000
    Messages:
    937
    Likes Received:
    2
    Trophy Points:
    0
    Hello Michael, thanks for the quick reply.
    It appeared to me that the fresnel had more of a satin appearance. The fresnel is definitely still reflective, but the contrast screen is almost like glass.
    I realize I can never completely eliminate reflections, even with duvetyne there will still be some. But I would like to take whatever reasonable steps are available to minimize them. Because the interior of the 533 is black plastic, I think a lens hood might be a faster and easier addition than duvetyne.
    Since I moved the contrast screen between the fresnel and lenticular I have noticed that the edges of images in high contrast areas seem to be a little jagged. It is very minor, but I am wondering if I am seeing the ridges of the lenticular?
    I'm going to try putting the contrast screen in the back of the stack tonight and then maybe taking it out completely. I need to settle on something very quickly, Bob (Mr. Bob) will be over to cal it tomorrow.
     
  4. Allan Jayne

    Allan Jayne Cinematographer

    Joined:
    Nov 1, 1998
    Messages:
    2,404
    Likes Received:
    0
    Trophy Points:
    0
    Be sure the smooth side of the fresnel faces back, towards the mirror and projection optics. This reduces halos, although the difference may be slight.
    The fresnel lens turns the ever spreading light rays from the CRT and lens assemblies to be parallel. If the fresnel is not molded with absolute precision to match the optics of that model of RPTV (it probably isn't), the rays won't be fully parallel. Then, the closer the fresnel is to the lenticular, giving the rays less distance to get out of position, the more correct the picture will be. Where the ray hits the lenticular screen rib is where a pixel will be seen to be.
    More:
    http://members.aol.com/ajaynejr/vidfres.htm
     
  5. Dan Driscoll

    Dan Driscoll Supporting Actor

    Joined:
    Aug 1, 2000
    Messages:
    937
    Likes Received:
    2
    Trophy Points:
    0
    Allan, thanks for the info and the link, it was very helpful.
     
  6. Todd Hochard

    Todd Hochard Cinematographer

    Joined:
    Jan 24, 1999
    Messages:
    2,312
    Likes Received:
    0
    Trophy Points:
    0
    I wouldn't put anything other than optical-grade glass at the back of the stack. It doesn't make any sense to me- why put a piece of plastic in the light path, if you're not going to use it for its intended purpose (to keep you from scratching the lenticular)?
    I wonder why it provides most of the rigidity, when on a set like mine (the Elite 510), it's optional? I've put mine on, simply because I have a young daughter getting ready to walk. I'll put up with the glare- I cannot put up with fingernail marks and crayon on the lenticular.[​IMG]
    I have noticed that on my 510, it actually can improve contrast. Of course, at all the wrong times. When the room is awash with light, the contrast screen does make the contrast higher, because it doesn't appear as white as the bare lenticular. Again, this is when the lights are up, or during daytime viewing. However, the crazy glare from my living room windows drives me to the 27" in the bedroom.[​IMG]
    I say remove it, and use spacers to make up the difference if necessary.
    Todd
     

Share This Page