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Screen door

Discussion in 'Projectors, Screens & Video Processors' started by phlashman, Apr 14, 2003.

  1. phlashman

    phlashman
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    I'm a noob and don't know what it is and/or how it's avoided.

    Could some one enlighten me. because i sounds bad as it has a kind of 'lock haw' vibe.
     
  2. nathan_silly

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    It's a side effect of LCD projection. It's the gaps between the pixels. For example, look closely at a laptop's screen. You can see a fine grid. This is screendoor- when a LCD matrix is blown upto 10' then the black grid is more noticeable.

    The higher resolution LCD matrix's will show less screendoor.
     
  3. phlashman

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    so it's the same as 'chickenwire'?

    is there anything you can do to make it better if you get it?
     
  4. nathan_silly

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    Yes, similar to chicken wire.

    Solutions..
    Make the image smaller
    Sit further away
    Get a better LCD PJ with a higher LCD matrix rez
    or buy a CRT PJ (superior IMO!)

    Also think if you defocus slightly it'll hide the screen door- at the expensive of detail.
     
  5. Anders_UK

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    Its a inherent problem with a fixed matrix projector, the DLP's suffer slightly more because as well as the spacings of the mirrors, you have to consider the area of the pedestal it is mounted too.

    I would say though with a decent res projector i.e. XGA or SXGA and a sensible size image, and viewing distance then you won't really notice it. The effects are less than what you get on a plasma.
     
  6. phlashman

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    thanks for your help. Hopefully it won't be a problem. I'll know tomorrow as i've just found out that thats when it arrives
     
  7. originalbadboy

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    Personally I dont see what the problem is .. I even see chicken wire at my local Cinema now that they have 'upgraded' to digital projectors ...

    I havent set up my AE300 yet (this weekend!) ... but I cant see it being too much of a problem , if you sit too close to your TV you are gonna see it as well. (Although your face would have to be pretty damn close!)
     
  8. Mr_Belowski

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    Yeah... people can get way too hung up on screen-door. Even when I sit too close to my Z1's image it doesn't really bother me. Yes I can see it, but as soon as I start watching the movie I don't notice it.

    Just enjoy your home cinema and if screen door bothers you, just drink beer till it goes away ;)
     
  9. SpiderManPants

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    LOL @ Mr_Belowski - That's what I'd do... :rotfl:
     
  10. Gary Lightfoot

    Gary Lightfoot
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    I just thought I'd point out that DLP suffers less from screendoor than LCD because the gaps are smaller - LCDs have to run the 'wiring' between the pixels, so the gaps are bigger.

    IIRC, LCD has a fill ratio of about 55% (45% is screendoor) and DLP is about 88% (12% screendoor).

    Rule of thuimb is to sit around 2 x screen width away (or more)from an LCD projected screen, and about 1.75 x screen width for DLP.

    As Nathan said, a common fix is to defocus slightly. Some other people have also said that using a lens filter helps to reduce it, and using a grey screen instead of a white screen can have a similar effect, though this is normaly only noticable when done as a comparison.

    HTH

    Gary.
     
  11. Anders_UK

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    Yeah the spacing is smaller but about 20% ish, of the mirror is taken up with the pedestal mounting area. So yes the pixels are closer but you have a black dot in the middle of them to consider aswell.

    Although I agree that you can't tell that much anyway LCD or DLP.
     
  12. Gary Lightfoot

    Gary Lightfoot
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    The dimple doesn't show as screen door, but allows more light into the image, reducing black level. I can't see the dimple reducing image transmission by 20% though.

    The 'dimple fix' is reputed to be out sometime later this year, and will increase DLP black level even further.

    DLPs currently have better black level than LCD, even without the dimple fix.

    Gary.
     
  13. Anders_UK

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    How can it allow more light into the image - and reduce black level...and how can it let more light in if there is no mirror space to reflect the image from??
     
  14. Gary Lightfoot

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    It allows more light (not image) through the dimple, and this reduces black level (more grey, less black).

    Removing the dimple will mean only reflected image is sent to the screen, and no stray light to wash out the image. Therefore you get an improved black level.

    Sorry if I wasn't clearer.

    Here's a thread you may find interesting, though it doesn't mention the dimple:

    http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=95686&highlight=repost

    If you look closely at the actual pictures (not theoretical), you can see the DLP dimple isn't visible, though in some of the actual LCD images, there is a dimple like artefact which I didn't expect to see...

    Gary.
     
  15. Anders_UK

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    OK, I see what you are saying now - the reduction in black level terminology is actually a worse effect. Should be the other way around. A reduction in black level is a good thing as this is measure in FL's as a absolute unit. So a reduction would result in an improvement.

    The pedestal that the mirror is mounted to takes up a percentage of total reflective area of the pixel, so you see a black square in the middle of each pixel. This obviously is a loss of image and reduction in aperture ratio, and from what you are saying the light reflects off of the top of this and still goes through the lens?? I am pretty sure this is a non-reflective surface (optical deadening).

    Anyway like you say the smaller the pedestal area the better the image quality we should get.
     
  16. avanzato

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    I can clearly see the dimples on the DLP XGA image.

    What is most interesting IMO is that all the real images look better than the theoretical ones. All those manufacturing tolerances seem to smooth the images out a bit.

    If I was buying a PJ again I'd have a more serious look at getting a DLP than I did before buying my Z1.
     
  17. Anders_UK

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    Yep DLP all the way for me...never even considered the 909's or 3 chip LCD's.
     

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