convergence

Discussion in 'Displays' started by SteveL, Apr 19, 2004.

  1. SteveL

    SteveL Agent

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    I have adjusted the convergence on my Hitachi Ultrascan rear proj. tv, but as you get farther(further) from the center the lines go off. Is this just the way things are, or is there some other way of adjusting the pic. that I am not aware of, perhaps I could get a pro to come in and adjust it?
    Any thoughts would be helpful. Hope I am in the right forum>
    Steve L.
     
  2. Dan Wesnor

    Dan Wesnor Second Unit

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    That's just the way things are. It shouldn't be real bad, but you'll never get it perfect at the edge.
     
  3. Jason Charlton

    Jason Charlton Ambassador

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    With RPTV's the CRT focus also worsens the closer you get to the edges and especially the corners - this may also be a cause for the problem you observed. That's in part why any manual convergence should be done from the middle of the picture outwards. In addition, I've been told that the blue CRT is often defocused slightly in many sets, though I'm not sure why or what purpose this would serve (perhaps it's related to the endless loop of issues that includes the tendency to give everything a bluish hue, the red push from overcorrection, and the resulting poorly designed color decoders... but that's a rant for another day [​IMG] ).

    Regardless, when I do a manual convergence on my set and get near the edges, I just do my best to center everything and make it as good as I can.

    -Jason
     
  4. Rick_FL

    Rick_FL Stunt Coordinator

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    edge and corner focus really isn't a top priority for manufacturers of CRT RPTV's. 99% of people focus their eyes onto the center of the screen, this is also where most of the action in movies takes place. Now if you use it for any computer work or videogames that may have static images in corners and along the sides, then it may be an issue. But with CRT RPTV's you really shouldn't be keeping static images on the screen for long periods of time.
     
  5. DustinLC

    DustinLC Supporting Actor

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    That might be true watching a movie but it is really annoying for me when I use my Direct TV guide where there's text everywhere, and also when watch movies with subtitles (the far left and far right.)
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    You should be able to get convergence very tight across the screen with proper adjustments. Electron beam focus at the edges may be problematic, but this is an advanced adjustment, and I am not familiar to the extent that RPTVs have good control over beam focus and astig across the screen. And it shouldn't really control the ability to have good convergence, unless focus is quite poor, and line thickness varies (i.e. one gun is well-focused, and another isn't, be that by poor optical, or poor beam focus), and then one line will be fatter than another until the source of the problem is corrected.



    Blue is often defocused (this is electron beam defocusing *NOT* optical focus!!! This has nothing to do with optical lens focus, don't go defocusing your blue lenses! [​IMG] ) to provide better grayscale tracking abilities at high-light output. It has little to do with redpush per se. However, to be able to provide a bright white field without losing blue output, perhaps you could say it is somewhat related. Blue defocusing is not equivalent to redpush as something to rail against. Blue is usually the tube driven hardest, we can't see blue very well anyway (difficult to focus on blue, just throw up blue and try to focus, it's hard to do). A large beam size allows for more phosphor to light, and thus be brighter. Otherwise, you will reach maximum output at blue before you do with the other two guns, and you will lose blue at the upper end of brightness as the phosphor saturates, which makes grayscale difficult to maintain in bright pictures, thus the defocus, which gives you that extra "oomph" to track grayscale properly.

    Edge and corner optical focus is another issue as well, that often does not have as thorough adjustments such as lens flapping as with CRT front projectors. Combine that with usually a shorter throw which requires more severe gun toe-in, and optical focus is difficult to achieve over the entire screen.

    *FYI: Electron beam, and Optical focus are two very different things. Optical focus uses lenses to focus the light onto the screen. The beam focus uses magnetic lenses in essence, to control the electron beam inside the actual tube.
     

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