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Silver Screen...?

Discussion in 'Projectors, Screens & Video Processors' started by cyberheater, Jun 13, 2003.

  1. cyberheater

    cyberheater
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    I've been reading some threads about using a silver screen which gives you the same dark blacks as a grey screen but with better gain.

    Has anyone else got any experience of these.

    Also, from a DIY point of view. How do I go about painting my screen silver. What kind of paint and technique?
     
  2. LV426

    LV426
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    I suspect that the danger with using silver is that you get some direct reflection from the projector lens - by way of a bright or 'hot' spot somewhere on the image, depending on where you sit. Taken to its extreme, imagine projecting onto a mirror - all you'd see is a reflection of the PJ - with a very bright spot where the lens is. Obviously a silver painted surface will be more diffuse, but, to an extent, the same thing will occur, I suspect.
     
  3. Anders_UK

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    Strange but true, there are two ways to improve contrast of a system by changing the screen properties. Theory is easier to understand if you are in a curved screen environment and you are sitting at the centre of the curvature.

    OK, if you have a screen gain of 1 (lambertian surface) then any light will scatter back and hit the other side of the screen, basically what is known as an integrating sphere. This has the effect of washing out the entire image and trashing your contrast.

    Now change the screen by reducing the gain this has the effect of absorbing more of the unwanted scattered light BUT reduces overall system brightness.

    Again, change the gain to a higher number. You may say that this will have the effect of scattering more light...yes but it scatters it in a more 'focussed' direction and if you are at sphere centre then it will be directed at you improving both contrast and system brightness. The major downfall is that a high gain coating is difficult to apply correctly, and a very big risk of image uniformity errors if the layout hasn't been done properly.

    A good idea if you can control the parameters that effect performance. However if you get a bad one it WILL be bad.
     
  4. zoolap

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    Sorry to interrupt the thread, but I can't help thinking of Highlander and its wooden lead actor :D
     
  5. cyberheater

    cyberheater
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    I've got a screen, blackout lining stretched over a frame and painted Icestorm 5. I went out today and bought some enable spray paint from Homebase. The colour says Aluminium and have just finished the first coat. I think another 2 coats will do it. I'll let you know how I get on!

    This thread inspired me to try this out. The difference using the silver screen looked amazing.

    http://www.avsforum.com/avs-vb/showthread.php?threadid=262466
     
  6. John_N

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    Hmm.

    The problem is that we are not in a curved screen environment for home viewing. Therefore using high gain screens brings all kind of problems. I'm sure this has been covered before in this forum and I'm getting a sense of deja vu.

    As you increase the screen gain you will reduce the angle that the screen can be viewed at without losing brightness. The same geometry appears in a curved screen environment except that the size of the "sweet spot" will get smaller and smaller so you have to sit/stand in a certain position.

    Also, because the majority of viewing rooms will tend to be relatively small and therefore use projectors with a short throw, the angle from the lens to the screen will be more extreme and hence the system will be prone to hot-spotting. This will not be as much of a problem in a system where the projector and screen are at opposite ends of a long narrow room.

    A high gain screen will reflect ambient light more efficiently than a lower gain screen, therefore the placement of the ambient light becomes more critical. Since most viewing rooms are lit by diffuse scattered light from a myriad of sources, using a high gain screen will not prove to be a good idea since it will be prone to wash out. There is no magic bullet. Contrast reduction in ambient light conditions affects all display technologies from plasma & CRT to front projection and is unavoidable due to the nature of the fact that the display is trying to show 'black' in an environment where light exists and no way exists of sucking light out of the environment!

    If you want to improve system contrast, the best thing you can do is to reduce the ambient light in the room using curtains and paint the walls a dark colour. In my viewing room the walls are dark red and this in itself makes a big difference compared to magnolia walls.

    As for spraying my own screen... the main issue again here is going to be uniformity of the optical coating. Just remember - just because a screen "looks" silver doesn't mean it will have the same optical properties as a spray on silver coat of paint, just like painting a wall icestorm grey does not have the same optical properties as a stewart grey screen.

    If you want to see the extent of the problem with a sprayed screen, just try showing a medium 50IRE grey field and see if you can see hot spotting. What you should see is a completely uniform grey field. What you will probably see is a grey screen brighter in the middle than at the edges, as if someone is shining a torch at the screen.

    All in all it might be fun painting the wall & screen grey or silver or whatever and believe me I've tried it, but overall you will get a better picture if you use a professional screen with gain of about 1.0 - 1.2 and try to cut out the ambient light in your viewing room.

    J
     
  7. theritz

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    I've done a silver screen and the primary difficulty is "hot-spotting" - the paint I used was not sufficiently matt. Another difficulty is getting a completely uniform surface - practically impossible without spraying, imo. Other concerns are a slight "push" on blue, and some "sparkling" - the mica in the paint I was using wasn't fine enough. Spray paint should be alot better though.

    I've located some silver material which is completely matt, and will be trying that out in a week's time or so.

    Where the silver was not hot-spotting though, the effect on colours was tremendous - far more depth to the image, an almost "3D" effect, and I can understand why Tryg over at avsforum was so impressed by it.

    Sean G.
     
  8. cyberheater

    cyberheater
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    Results: A bit of a disaster. theritz is right. You need a completely uniform surface cause the silver really shows any underlying surface structure.
    I will experiment with some mdf board.

    Also, hotspotting was a issue. Is there any thing I can spray on top of the silver to 'matt' is up a bit. Suggestions welcome.

    It has to be said that when you get the angle right. The colours do leap off the screen. I think this could be quite promising.
     
  9. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    I've viewed the VutEC SILVERSTAR 6 gain screen material that seems to be becoming more popular. I found it quite nasty to look at. White detail seemed crushed somehow and black level was raised. It was bright in a bright environment but for home theatre use I feel you are wasting your time going down this route.

    Gordon
     
  10. John_N

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    No surprises there (about the disaster). I think you really are wasting time and money. Even if you try and make the coating more 'matt' it will still hot-spot. It is not easy to make an optically uniform coating. This is why projector screens are expensive. Spraying a coating using a spray-can will likely still not be good enough because the particles from a spray-can are too large and not uniform. Even if you use a compressed-air professional spray-gun and use a professional operator to spray it to produce a car-paint type finish, it will still not work very well because the materials that make up paint are not designed for projector screen use and hence are not designed to reflect all colours of the spectrum totally evenly, scatter evenly, or even to have totally uniform reflectance throughout the mixture - since paint is a mixture of substances and is not designed to stand up to intense scrutiny.

    I considered the viewtex silverstar 6.0 material and like Gordon I didn't like it after viewing a sample. There really is no such thing as a free lunch or a magic bullet.

    Lose the ambient light and calibrate the projector properly. It really is the best way...
     

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