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Help a newbie...rainbow effect with a CRT?

Discussion in 'Projectors, Screens & Video Processors' started by Nebby, Apr 6, 2004.

  1. Nebby

    Nebby
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    Hi All

    I've just begun to dip my toes into the wonderful world of CRT!

    I've recently purchased a second hand Seleco 320...

    While I have the option of paying for a professional install, I am keen to learn more about this new 'toy', and have had a crack at setting things up myself.

    After a few nights spent tweaking under dimmed lights, I'd say I'm within touching distance of a nice picture. However...

    The CRT is currently connected to a DVD player (Pioneer DV-353)by SVHS cable (will switch to component video output soon). When watching a movie (I've tested a few), I seem to be experiencing what I can only liken to a 'rainbow effect' if I happen to glance away from the screen. This sometimes occurs if the action involves fast movement.

    I've experienced the 'rainbow effect' before when looking at a dlp projector, but was under the impression that I shouldn't experience the condition with a CRT. This leads me to believe that I've gone wrong somewhere during set-up, although I've started from scratch two or three times now, just in case I' missed something along the way.

    While I'm happy to pay for the professional install, I can't stand being beaten! Given my lack of CRT experience, if the above suggests a particular problem or setting I need to look at, I'd be most grateful for any help / advice.

    Cheers
     
  2. mrxfilms

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    Don't panic, i think you'll find this is normal. I run a Barco 7LT froma Denon 2900 and expereince the same. The PJ was professionally installed. You may find that you are particularly sensitive to the effect. I found that DLP gave me a headache and was very distracting, whereas with CRT it is only on light against black, and in fairness you do have to exagerate your eye movement dramatically to see it. Sit back, relax and enjoy the world's best projectors.... CRT
     
  3. Nebby

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    Hi mrxfilms

    Thanks for the reply and encouragement. I guess I'll keep tweaking...it's all part of the fun, I guess...and experimenting with "Y/C delay", "blue stretch", "peaking", "comb filter" and so on.

    Do you think there's some kind of conspiracy going on with av equipment manufacturers? The manual that came with the Seleco is a classic...it shows you how to adjust the settings outlined above, but then fails to explain what effect any adjustment will have on the picture!!!

    Do you know of any glossary's that I might find on-line, that explain these dark arts?

    Nebby
     
  4. cessquill

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    I've got a fair amount of information with just google searches. My manual is the same. Yes, I'm aware how to turn things up and down - all the settings adjust exactly the same. I want to know what they do.

    Some of the Italian-English translation in mine means that when they do try to explain, it just sounds like rubbish.
     
  5. mrxfilms

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    Hello Nebby,
    There is a web site called crtprojectors.co.uk who have bags of info on CRT's. They have a slight bias towards Barco but plenty of info on others. When i first decide to go the way of CRT 2 years ago, this site provided a good grounding of info. Print the FAQ section out and you will have plenty of toilet reading.
    Regards
    Pete B
     
  6. LV426

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    Some 'experts' initially deny that CRT rainbows are possible. Indeed, a few years ago at 'The Event' I saw this effect, commented on it, and it was dismissed as imagination by the expert presenter.

    Yet there they are. Others have seen them too (although very few people have 'fast' enough vision).

    I can only assume that the the coloured tubes are not energised concurrently, but consecutively, and, coupled with the intermittent nature inherent (ie unavoidably flickering) of any CRT presentation, this does indeed produce, effectively, the same thing as 1-chip DLPs do.

    To reduce (but never remove) it for a CRT you need to use an external scaler to ramp up the refresh rate as high as the projector will take.
     
  7. Nebby

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    Hi Pete

    Just had a quick look at the site you suggested...looks like I've got plenty of reading material!

    Thanks for the help
     
  8. Nebby

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    And thanks to you too Nigel...although I have to admit, being such a newbie I only understood the last paragraph of your post (I tend to pick up on things that involve spending money!) and, of course, your sign-off reference to one of the greatest movies ever made!
     
  9. Jeff

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    This has a serious impact on picture quality, if you see rainbows on CRTs and flicker bothers you a lot then I would suggest that CRT isn't a solution for you.

    Despite the fact that I see rainbows on even the best single chip DLP projectors and 50Hz bothers me on large(28"+) CRT TV's, I run my CRT projector at 48Hz for NTSC film and 50Hz for PAL and enjoy the experience greatly.

    Each to his own as they say.
     
  10. chrisgeary

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    yes i can detect a slight rainbow effect with my 801s, but i have to rapidly move my eye from left to right to get it (a thoroughly unnatural experience - even after a bottle of wine!) - just moving your eye from the left of the screen to the right isnt enough - so i never notice it! if you haven't seen an LCD or DLP projector, you should.. you only have move a millimeter and the rainbow effect strikes!
     
  11. LV426

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    Do you mean that BOTH DLPs AND LCDs have rainbows?

    If yes - you are seriously misguided. Although they aren't without their other shortcomings - LCDs do not, and never have, suffered form any rainbow or any other temporal artefact. They all produce a constant, unflickering image (assuming, of course, that they are working correctly).
     
  12. chrisgeary

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    yeah i have seen LCDs produce the rainbow effect. i have a friend who has a compaq jobby.. its very noticeable. no its not DLP ;o)
     
  13. Jeff

    Jeff
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    Nigel, see what you've started. Rainbows on LCOS anyone?
     
  14. LV426

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    I started it?

    I'm sorry chrisgeary. With some (only some) knowledge about how these things work I seriously doubt that what you saw was anything other than the product of a deranged mind. In any case, if true in the specific case, it's probably unique; certainly very very rare for an LCD to produce any kind of temporal artefact. Really - they just can't.
     
  15. Jeff

    Jeff
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    Isn't this what was said when you claimed to see rainbows with CRTs? :)
     
  16. rob_w

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    I can catch a rainbow on my barco 800 (720x480x72Hz):(

    But only with white on black stuff (credits etc), and only if I move my eyes about.....

    My old dlp on the other hand :rotfl:

    Never noticed it on lcd though....

    Could it be linked to the screen gain? - I use harkness hall perlux140. Meant to be quite a small viewing angle.

    Rob
     
  17. chrisgeary

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    nigel: i really don't appreciate your tone. so far you have stated that i have a deranged and misguided mind without any real reason. i think you could show some respect for the views and opinions of others. why must you resort to patronising personal attacks rather than just debating the issues and opinions presented?
    the thread is rainbow effects with CRT. perhaps we are not talking about the same thing so ill be clear about what i mean: i have seen, quite vividly, a streak of multicolour as my eyes move from one part of an LCD projected image to another. i can barely discern it with CRT, as can the thread-starter and as mrxfilms stated, you have to really try to see it. i stated that it is much more noticeable with LCD/DLP forgetting that nebby already knows this! duh, sorry.
    you seem quite sure that your view is the only and correct one regarding LCD and rainbows and that my experience is invalid. yet by your own admission in other threads, some people see it, some don't. so can you not accept that i can see it, really quite vividly and am not deranged nor misguided?? perhaps there was some other factor that lead to me seeing it, and it was not the LCD equipment at all.. perhaps the DVD player and the connection used at the time. so lets hold the personal comments eh?

    Chris

    *white flag*
     
  18. LV426

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    I'm sorry.

    Let me put it another way.

    LCDs don't produce a rainbow effect. At all.
     
  19. rob12770

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    No Lcd's dont, I have notice this phenomenon on crt, but I would not call it a rainbow effect, I have noticed its worse if the convergance is not right, thus I have come to the conclusion that is all it is, when properly converged I cannot see it even if if i scan quickly accrosss the screen. suggest this topic be closed.
     
  20. Nebby

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    Hi rob12770

    This is just what I wanted to hear! I can't look at some dlp's for more than a minute or so, before pretty patterns start to appear before my eyes. Never had the problem with my Mitsubishi lcd...just a naff picture. If what you're suggesting is that my crt "rainbow" problem is due to how I've set the pj up, then I'll be a very happy bunny! Guess it's just a case of try and try again...

    To confirm, when you say 'properly converged', you mean the red, green and blue tubes should sit perfectly, one on top of the other, don't you...not just 'hidden' behind the green?
     
  21. rob_w

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    Just because you've decided that its bad convergence that causes it doesn't really close the topic. I for one would love to know if more people see this on crt's.., and whether they all have badly set up projectors.:confused:

    Cheers
    Rob
     
  22. LV426

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    When I said I'd seen the effect, the first time, it was on a high-end piece of equipment which had been specifically set up to show it at its best - at the first 'Event' in Glasgow. Those who know what I mean by 'Event' will know that the projectors there were all giving of their absolute best. So - yes, they were converged exactly right. I can't tell you exactly what equipment was in use, but I'm pretty sure it was about as good as it gets.

    The next time I saw the effect was at a show at the Renaissance in Manchester in 2002?. The Denon room had, in it, TWO Barco CRTs plus associated scalers and so on - those more directly involved will say what - and, again, had been set up by real experts in the field. Again, they were (all 6 images) converged right.

    On this occasion - on this VERY forum - several others also commented that they had seen rainbows.

    I may be wrong, but, perhaps the common factor in these two experiences is that, in both cases, the screen was very large in relation to viewing distance - exactly how Home Cinema should be.
     
  23. rob12770

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    Nothing that I have decided Rob, I just dont see the point in bitching at each other ?
     
  24. rob_w

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    ""I just dont see the point in bitching at each other ?""

    Fair enough, ain't all of us bitching though;)

    Rob
     
  25. cosmic023

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    I see rainbows on my BD801s.......i'm just glad it's nothin' like an DLP unit !!

    And 'm running the same resolution as Robwells....

    720x576@75hz PAL Material
    720x480@72hz NTSC Material
     
  26. Roland @ B4

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    I have set up close to a 1000 CRT's over the years. I set up both projectors that Nigel refers to, the first was a Barco 808 the second a double stacked Barco 1209 and have I never experienced what I could call rainbow.
    I would be interested if the same effect can be seen on standard CRT televisions are the refresh rate will be low but the phospors will be pretty much the same.

    There are a few people who have glasses that have cromatic problems bending light at differnt angles.
     
  27. rob_w

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    Hi Roland,

    It's not noticable except on thin white lines against black/ dark backgrounds. Try freezing some credits then look straight at the line, then flick your eyes up / down (for horizontal white line/ text), or left/right for vertical lines.

    I don't wear glasses for viewing films (yet!). Maybe it's the same as why some people can't see rainbows on DLP machines. I'm pretty sure I saw blue flashes in the moonlight scenes in Pirates of the Carribean at the little odeon Leicester sq, and that uses a 3 chip machine I believe. - I also notice 'judder' on pans at the flicks too..

    EDIT - never notice it on my TV though (phillips 32"). That's just got a crap picture:(

    Cheers

    Rob
     
  28. LV426

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    ....and I have absolutely no doubt that they were all giving of their absolute best.

    I guess I should say that, at least as far as the Glasgow Event was concerned - I honestly wasn't expecting to see the rainbow effect with CRT technology. When I did see it, it came as a complete surprise. I wasn't looking for it. But there it was. Much less obvious and less nauseating that with 1-chip DLP. But there, nevertheless.

    I guess one way to prove this might be to take either still or movie photographs of the screen image, using a shutter speed on the camera much faster than the refresh rate of the device. This would, I guess, reveal any temporal artefacts.
     
  29. Chris Frost

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    Like Roland, I have set up more CRT projectors than I care to remember, but unlike him I have seen an effect similar to DLP rainbow, but I believe it is more of a 'persistence of vision' thing.

    I can get the same effect flicking my eyes across my PC screen as I type this reply. I am also convinced I could replicate the effect with a high contrast image painted onto card so eliminating any question of this effect being caused by CRT or even three chip DLP.

    My own thoughts as to the likely trigger for this phenomenon is a combination of image brightness and high contrast.

    As for judder in cinema images, I think that is more to do with the frame rate of film (24 f.p.s) producing an animation type effect whenever the camera is panned or there is fast movement across the frame. And yes, it drives me nuts too :)


    Regards
     
  30. LV426

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    Persistence of vision? Plausible, I guess. Is your PC monitor a CRT item? I can't say I've seen anything similar with my LCD monitor - but - as you say, that may be down to lesser contrast.

    One of these days, I will get around to photographing some displays and see, for sure, what if any temporal artefacts there are.

    As for judder - it is an inevitable by-product of a sequence of still-frames. If the camera shutter speed is too high, especially. A prime (intentional) example is the early fight scene in 'Gladiator'.
     

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