RPTV and Optimal Focus

Discussion in 'Displays' started by Dave H, Nov 10, 2005.

  1. Dave H

    Dave H Producer

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    I have a one year old Sony KP-57WS520 (CRT RPTV).

    Can my TV be considered to have good focus if the scanlines are very defined close-up....and even sometimes slightly noticable by sitting 10 feet away? Is this a good test?

    I'm just asking, as I was wondering if they could even be improved upon. However, my ISF tech who calibrated the set said the focus was good and didn't think he could get it better. I've also heard Sony RPTV have good focus out of the box.
     
  2. ChrisWiggles

    ChrisWiggles Producer

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    Yes this is good generally, but obviously you don't want to see the scanlines so you'll want to be running a high enough resolution that they aren't visible, or be sitting far enough away. Keep in mind that there are two projection systems in a CRT projection display, the tube itself/beam setup, and optical focus of the tube to the screen surface. If there is a "focus problem" you need to understand that there are two systems and problems can be caused by either. If things are well-focused at the screen, this indicates that both are working well and setup properly. Also keep in mind that you should check all three colors independantly, because it may look like you're resolving scanlines on white for instance, but it may only be one color and the others are not well focused. Also rememeber that blue is both difficult for your eyes to focus on so it will never appear as sharp, in addition it is often electronically defocused slightly for better light output/linearity.
     
  3. Dave H

    Dave H Producer

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    I went into the service menu and shut off two colors at a time (using the service manual). Red and green were extremely sharp...the scanlines just as visible as before.

    However, when I viewed blue by itself...NO scanlines were visible at all. And, the service menu text of the screen was slightly blurry..not nearly as sharp as red and green as you suggested.

    Is this normal? It makes me think it was done deliberately or that it's the best it can do. What do you think?
     
  4. ChrisWiggles

    ChrisWiggles Producer

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    I said: "Also rememeber that blue is both difficult for your eyes to focus on so it will never appear as sharp, in addition it is often electronically defocused slightly for better light output/linearity."

    [​IMG]

    So it is not abnormal. If is is terribly out of focus then there is a problem. Viewing a dots pattern can help the dots will sill seem somewhat blurrier than the other colors, but should remain about the same size of course.
     
  5. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Blue will always be fatter and less focused than the other two colors. Regards
     
  6. ChrisWiggles

    ChrisWiggles Producer

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    indeed! blue needs the atkins diet! [​IMG] [​IMG]
     
  7. Dave H

    Dave H Producer

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    I understand what you are saying. But, I have a question.
    Just curious...when doing manual focus (twisting the lid of the pot for the CRT) for blue....if someone doesn't get it quite as sharp as it's capable....say just a bit off.....will this be perceivable during normal viewing? I mean if it's not as perfect as it's possible. I know blue can't get as sharp as the other two colors....but if someone doesn't quite "maximize" the focus for blue, doesn't really matter?

    I've heard it's not quite as important for blue to be as focused as you can make it; it's really with red and green.

    I'm just trying to understand the nature of blue here.
     
  8. ChrisWiggles

    ChrisWiggles Producer

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    Yes and no. I mean, obviously at some point you're going to lose a sense of sharpness and detail as the blue beam (not the lens!!!) gets out of focus. If it's a little bit off, I don't think you will notice much at all.

    The blue beam is often intentionally defocused slightly, this gives a larger spot size and increases light output, because the beam intensity is spread out over a larger area. If very tightly focused, the beam will saturate the phosphor and blue light output will max out. Defocusing slightly can increase the blue light output headroom and help maintain good grayscale tracking through bright whites.

    You may also notice that if you are focusing the blue beam, it may be very difficult to tell where it is most focused. Generally, you'll see a large range where it doesn't seem to change much, and looks about as focused as it's going to get, yet still appears sort of fuzzy because of your poor ability to focus very well on it. Being familiar with the fact that blue light output will decrease as it comes into very tght focus with a bright line, you can pay attention to the much smaller zone of adjustment where light output decreases slightly. This is the most focused spot for blue. If you need to maintain more blue output, you can defocus from this slightly just until you get that increase in light output, but no more. Paying attention to this light output change is an excellent way to see where blue is best focused, regardless of your eyes' abilities.

    hope that helps!
     
  9. Dave H

    Dave H Producer

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    Yes, it helps alot! I had my ISF tech out and he re-did focus. I just noticed when he was doing blue, it seemed very hard to do with the beam (or pot). The electro seemed easier. But, for beam, it almost seemed like a certain small range was good and that it may or may not have been quite perfect. I mean hard to tell! Kind of hard to explain, but I think you pretty much know what I am trying to describe. If anything I know he got it in the 95-99% sweet spot correct range. With the other two colors, it was much easier and like 100% accurate. I just wondered if being off very slightly with blue, if it would even be perceivable when watching movies. And, it sounds like it would not be.
     
  10. ChrisWiggles

    ChrisWiggles Producer

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    sounds good then, you won't really notice it at all unless it's off a significant amount, and even still a lot of people wouldn't notice it still.
     

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