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Haloing effect on CRT

Discussion in 'Projectors, Screens & Video Processors' started by Boris Blank, Jul 19, 2002.

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  1. Boris Blank

    Boris Blank
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    Thought I'd post this just to let you see something odd - haloing around bright objects. The effect is barely visible on the screen but on investigating further and removing the lens from my crt, this is what it looks like on the tube face itself.

    The haloing covers almost the entire tube face, not just the raster area.
    Paul
     

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  2. Boris Blank

    Boris Blank
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    And this is what its like once I turned the brightness up (beyond an acceptable level).

    Paul
     

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  3. Boris Blank

    Boris Blank
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    Looks horredous on the tube face but on the actual screen it ain't too bad at all. Oh, the movie is Pitch Black by the way and its the exact same scene in both pictures. I'd noticed some haloing whilst watching the movie and tried to figure out whats going on and why.

    Thought it was a reflection at first but its the tubes themselves. The photographs are with the lenses off looking directly at the tubes.
    Paul
     
  4. Roland @ B4

    Roland @ B4
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    Pic 1 is light relecting withing the lens and back onto the CRT face. They do that I'm afraid green and blue are most noticeable. That's why liquid coupled lenses are slightly better. However it shows your black levels are set right.

    Pic 2 It gone becasue you are illuminating the raster hence no reflection.

    What's the projector as a matter of interest?
     
  5. Roland @ B4

    Roland @ B4
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    Oh now! he says the lenses are off..:blush:

    the only thing I can think is that light being spread out from the bright bit
     
  6. Boris Blank

    Boris Blank
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    Hi Roland,
    Really weird (and interesting!) isn't it! This is on a Barco 801s - I had adusted the G2 a few days ago after accidently twisting the wrong knob whilst tweaking the focus. Actually made quite a good job on the colour temp but noticed (after a few movies) that bright objects in dark scenes had a VERY faint halo around them, also noticed some faint horizontal streaking as well.

    I investigated it all this afternoon finally taking off the lens to check if it was indeed a reflection from the lens only to find its the tubes themselves (they all have it). Checked sources etc but definately tube related as far as I can see. Talking about it on the AVS forums, others have the same thing or have seen it in other crts but no solution as yet other than re-setting brightness/contrast levels.

    It does seem very odd though in that all tubes have it - seems like its not so much of a fault, rather its a combination of things coming into play perhaps?

    There is a good discussion of it here;
    http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=147698&perpage=20&pagenumber=1

    I wonder if maybe the haloing is quite common but most folks don't actually notice it - certainly the guys in the thread that went to check on it found they could see it?

    Paul
     
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