1. Join Now

    AVForums.com uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

DLP Convergence

Discussion in 'Televisions' started by NPM108, Feb 28, 2005.

  1. NPM108

    NPM108
    Standard Member

    Joined:
    Nov 6, 2004
    Messages:
    109
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    16
    Ratings:
    +0
    Hi,

    Am curious to know whether all DLPs suffer from horizontal convergence issues at the top of the screen.

    I can only use the Sammy SP46 as an example, but when the screen is not in full widescreen mode and has the black colour bars at the top and the bottom, the top bar has a downwards sloping bend, whereas the bottom of the screen is dead straight (horizontal)

    A mate told me this was well documented on all DLPs....? Is this the case with the Tosh and Sagem models, perhaps owners of these sets can confirm?
     
  2. LV426

    LV426
    Administrator Staff Member

    Joined:
    Jul 14, 2000
    Messages:
    12,789
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Somewhere in South Yorkshire
    Ratings:
    +4,984
    First up - terminology:

    Convergence refers to the alignment of the three colours that make up a TV image. Poor convergence occurs when the three different coloured images are not in the same place on the screen. The result is coloured fringing around the edges of objects. Poor convergence can't occur on a DLP machine unless there is something very, very, very wrong with it. It's also referred to as alignment (in LCD projection).

    What you are describing is poor geometry. Poor geometry on a CRT device is quite common, and can often be improved with service menu tweaks. In the case of DLP RP devices (or LCD for that matter), it can only occur as a result of poor optics or some mechanical misalignment of components; it isn't electrical/electronic in nature and hence isn't a matter for a service menu tweak or other electronic setup issue. And I have to say that the majority of DLP RPs I've seen (in the likes of Curry$, Dixon$, Com€t etc) have had some bowing evident on one or more sides of the image.
     
  3. n00b

    n00b
    Active Member

    Joined:
    Nov 27, 2004
    Messages:
    315
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    18
    Ratings:
    +17
    thanks for clearing that up, i too had the wrong idea of what it meant. i assume the mechanical misalignment of components can be corrected by an engineer.
     
  4. LV426

    LV426
    Administrator Staff Member

    Joined:
    Jul 14, 2000
    Messages:
    12,789
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Somewhere in South Yorkshire
    Ratings:
    +4,984
    I assume so - given that they aren't all equally bad. However we may be straying into the grey area that is "manufacturing tolerance" here..... I wish you well.
     
  5. NPM108

    NPM108
    Standard Member

    Joined:
    Nov 6, 2004
    Messages:
    109
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    16
    Ratings:
    +0
    Thanks for clearing that up, my mistake and good to know. The Bending effect isn't too bad, but was just curious as to possible reasons why
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
    Distinguished Member AVForums Sponsor

    Joined:
    Jul 13, 2000
    Messages:
    13,982
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Living in Surrey, covering UK!
    Ratings:
    +2,786
    As Nigel says it's due to optics. It is unlikely it's fixeable. In a rear pro it's more than likley that most manufacturers are using the same through length lens and, who knows, may be even from the same manufacturer. The lens s what will be creating the barrel distrotion. It is present on some fo the cheaper DLP front projectors too....it doesn't have to be that way....just you need to pay more money.

    Gordon
     
  7. Chris5

    Chris5
    Active Member

    Joined:
    Mar 21, 2004
    Messages:
    1,161
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    63
    Location:
    Herts., uk
    Ratings:
    +122
    having said there are no convergence errors on DLP my green pixels ar misaligned from the red & blue by about 0.5 mm.

    Gordon, I assume u wont be able to help there when you come and ISF it next month.

    Chris
     
  8. Gordon @ Convergent AV

    Gordon @ Convergent AV
    Distinguished Member AVForums Sponsor

    Joined:
    Jul 13, 2000
    Messages:
    13,982
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Living in Surrey, covering UK!
    Ratings:
    +2,786
    Chris,

    The misalingent you see is nothing to do with pixels not being converged. It's the same pixels doing all the colours. The difference will be in how the different frequencies light are refracted through the prisms and lens. It's not fixeable...

    Gordon
     
  9. Chris5

    Chris5
    Active Member

    Joined:
    Mar 21, 2004
    Messages:
    1,161
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    63
    Location:
    Herts., uk
    Ratings:
    +122
    ok, I thought it might have been a timing issue with the wheel, you think this is normal then? I thought it odd that red & blue match perfectly, it is only the green that is out. it gives a green tinge to one side of white text, and purple to the other (you have to stand close to the tv to see it though).
     
  10. Gordon @ Convergent AV

    Gordon @ Convergent AV
    Distinguished Member AVForums Sponsor

    Joined:
    Jul 13, 2000
    Messages:
    13,982
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Living in Surrey, covering UK!
    Ratings:
    +2,786
    It might be a chroma delay issue...The alignment of pixels is the same regardless of what colour is being displayed.

    Gordon
     
  11. Chris5

    Chris5
    Active Member

    Joined:
    Mar 21, 2004
    Messages:
    1,161
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    63
    Location:
    Herts., uk
    Ratings:
    +122
    anyway Gordon, I look forward to meeting you soon.

    Chris
     
  12. LV426

    LV426
    Administrator Staff Member

    Joined:
    Jul 14, 2000
    Messages:
    12,789
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    166
    Location:
    Somewhere in South Yorkshire
    Ratings:
    +4,984
    Chromatic aberration. (Poor quality lens). At a guess.
     
  13. Chris5

    Chris5
    Active Member

    Joined:
    Mar 21, 2004
    Messages:
    1,161
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    63
    Location:
    Herts., uk
    Ratings:
    +122
    but you would expect that to split red from blue even more than red from green, but it does not, red & blue align precisely
     
  14. NPM108

    NPM108
    Standard Member

    Joined:
    Nov 6, 2004
    Messages:
    109
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    16
    Ratings:
    +0
    Guys,

    I had some time to spend this afternoon and have measured the bend effect.

    At the centre of the screen there can be a variance of between 0.5cm and 0.8cm more than on the left and right (although even these vary).

    As you can imagine nearly 1cm creates a noticeable dip down in the centre at the top of the picture when viewing widescreen dvd's which aren't full screen.

    When they are full screen and there is text near the top I've noticed that even that text bends.

    Given that I also have a noisy colour wheel issue on this set and that is only 1 week old, would you say I have a lemon and should return it? As this means not only do I have this geometry issue but also a excessively noisy colour wheel.

    Thanks.

    P.S. Will post pics when the camera's batteries are charged
     
  15. ducati748

    ducati748
    Guest

    Products Owned:
    0
    Products Wanted:
    0
    Ratings:
    +0
    hi NMP108 , hi had almost identical problems with my tosh 46 . I phoned tosh support and they told me lines should be totaly straight and i should not be able to here colour wheel or fan over speakers - even at low volume . i had a comet engineer out who confirmed this and am getting a replacement set next week .

    imho i would get the set exchanged .

    anyway hope this helps
     
  16. NPM108

    NPM108
    Standard Member

    Joined:
    Nov 6, 2004
    Messages:
    109
    Products Owned:
    0
    Products Wanted:
    0
    Trophy Points:
    16
    Ratings:
    +0
    Well its hard to see the bending from these pictures but none the less I have attached them. The black background makes it hard to see the dip but its there!!
     

    Attached Files:

    • 1.jpg
      1.jpg
      Size:
      69.9 KB
      Views:
      127
    • 2.jpg
      2.jpg
      Size:
      76.7 KB
      Views:
      147

Share This Page

Loading...