DLP vs. CRT

Discussion in 'Archived Threads 2001-2004' started by Robert P. Jones, Mar 16, 2002.

  1. Robert P. Jones

    Robert P. Jones Second Unit

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    The following are some comments I made recently at the SPot, in reply to some questions on this issue. I thought I'd share them here also.

    ALL the DLP RPTVs I have seen yet, including the ones I saw at CES in January, have optics that are made for the pricepoint, and show it. As such, they all have refraction error for the entire last foot or so of their picture, at both the right and left sides.

    This appears as/looks like convergence error, but of course is not. No convergence error possible on these, since they are single chip with color wheel, and as such use only one lens.

    Which means that the extremely short throw causes this irritating refraction error once the angle from center is great enough. Which of course is at the sides.

    With CRT technology, we can make those areas perfect. With DLP technology, we cannot. We are stuck with those refraction errors for a full foot of picture on each side.

    Other than that, and the fact that they will always be just a little more pixellated than CRT whenever you are sitting close enough, they're great.

    But I would want a display device where any convergence error could be corrected essentially completely, as in the current CRT systems - Mit has one of the best - and where there would be none of this distracting refraction error.

    Fully and properly tweaked, my 65" last year's CRT-based Panny has it all over anything I saw at CES, as far as DLP goes. No DLP RPTV will beat it. As far as I am concerned, that goes for the Mits CRT-based units also, once fully tweaked.

    Except for the master DLP projector at the Texas Instrument booth, the one Lucas is touting as the future of the movies we go out to see, and where he wants to show his future Star Wars movies, being digital as they will be - Episode II was shot completely in digital.

    The huge picture from this movie theater grade projector was picture perfect, having no short throw to have to worry about; it will save tons of money in not having to make and transport cumbersome reels of the miles of film it currently takes for our mall theater movies, its anamorphic lenses are custom made per projector by Minolta, and only costs the theater using it $250,000...

    Mr Bob
     
  2. Robert P. Jones

    Robert P. Jones Second Unit

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    A question was asked in the Mit forum about the density of the mirrors vs. the pixels/resolution. This is an answer to that question, thought I'd share it here also.

    With DLP - Digital Light Processing - another word for MMMD - Moving Micro Mirror Device - each mirror is a pixel, direct linkage.

    The 2002 DLP RPTVs I saw at CES, no matter what the brand, are all 720p capable, as are also the plasmas for 2002. With the CRT based RPTVs, you had a hard time finding 720p capable this year because Panny, which was almost the only native 720p capable one the year before, has now gone to having the 720p be downconverted to 1080i, because it's cheaper that way. Evidently conversion circuitry finalizing in 1080i is cheaper than native circuitry for each. This is straight from the head service section cheese at the Panasonic booth. A very spectacular and huge section - "booth" is actally a massive understatement on my part, truth be told - I might add, it really blew me away.

    The chip used in the big guy for the mall theaters has a 1280 x 1024 pixel/mirror device/array in it, squeezed down to 16x9 or whatever the "filmed" aspect ratio of any particular movie will be, via anamorphic lensing - which of course the theaters in the malls have been already been using for decades, to get cineramic widescreen up there. This of course would improve vertical resolution, by an optical anamorphic squeeze factor of 1024 down to 720, or roughly 4 to 3. Therefore the mall theater projector will have an image that will be substantially tighter than the RPTV projector. It has to. Its projected image is huge, in comparison.

    The ones used in the 16x9 HDready RPTVs are actually 16x9 arrays, with evidently ? x 720 pixels, or mirrors. The math would call for 1280 for the question mark, tho I don't know the exact specs from them.

    I did see the 16x9 TI chip at Runco when I attended their onsite training, shortly after the ISF training I attended there in Hayward, in November of '01. This is evidently what everybody is/all the brands are using this year, as TI has the proprietary monopoly on this device.

    I also learned while I was there - and this is straight from Sam Runco, at a pre-briefing to AVS Forum members an hour before the actual press briefing addressing the same issues: their new products - the truth behind the allegations that Runco is just a re-badger of other brands. Sam was looking particularly dapper and well dressed for his meet with the press, immaculate dark - pinstripe, as I recall - suit and tie, with not a thread or a strand of hair out of place, a mode I had not seen him in before. I also observed that all the guys at the Runco booth had fresh haircuts...

    The truth is that they not only rebadge them, they get in there and substantially redo the circuitry and programming, to their own and usually much more demanding specs, specs that are sometimes not even still within confining NTSC standards and are actually Runco proprietary, for making their CRT based units look so dazzling as they do.

    In this case, Runco has actually sought and received from TI the key to TI's back door, for revamping whatever TI DLP chips Runco uses. That is why a Runco will, as usual, look substantially better than a similar device that does the same thing.

    This "look" is true of plasma as well as DLP. And they blew the press away with their new products for this year, esp. with markedly decreased pricepoints on the newer technology equipment.

    They blew us away also, at this private AVS Forum showing, and it's not easy to blow away a SPottie OR an AVS Forum member.

    At this pre-briefing he also stood by CRT-based technology and said they have no plans to discontinue producing CRT projectors, because CRT is still the only medium which can accurately and faithfully capture true blacks.

    Mr Bob
     
  3. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Q ... So what are those momentary convergence error flashes that I see on the units like the Runcos and Dreamvisions and what not? On the less expensive DLP units, I see this "flash" of R/G/B colours every minute or so.

    On the better more expensive units, I see it every 3 minutes or so ...

    I find that effect maddening and wonder if it can be stopped? Simply cannot see myself getting a unit like this until this issue can be solved.

    Regards
     
  4. Robert P. Jones

    Robert P. Jones Second Unit

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    Sorry, have not observed anything like this. I didn't sit down and watch an entire episode of anything, or entire movie.

    However, I have heard of a rainbow effect on DLPs, where the remedy is to speed up the color wheel to about 3 times normal, or something like around 400 rpm. I believe 180 rpm is normal.

    Mr Bob
     
  5. Allan Jayne

    Allan Jayne Cinematographer

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    If your eyes move at just the right time in just the right direction as you follow the movement of subject matter on the screen, you see color fringing. Some people are more sensitive to this than others.
    It can't be eliminated completely in a system that utilizes a color wheel. It is just minimized by spinning the wheel faster which also means having the DLP chip flip between red, green, blue content faster in sync. with the wheel.
    Folks who are sensitive to this color fringing will have to stick to alternate video technologies, such as CRT or three panel LCD (3 panel DLP is much more expensive and therefore rarer).
    (The refraction error referred to above is known as chromatic aberration. The lens acts as a prism causing light to be split up into component colors as in a rainbow. Using several lens elements made up of glass with different densities (more correctly, indices of refraction) (at added cost), chromatic aberration is reduced.)
    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     
  6. John Kotches

    John Kotches Cinematographer

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    Michael,

    You are seeing what everyone else calls "Rainbows". Some individuals are sensitive to them, others are not.

    The faster the color wheel spins, the less likely you are to see them. On the 5x wheels (Marantz and Sharp FP units) I have never seen a rainbow. On my NEC LT-150 I saw them constantly at first but now only see them occasionally. I think you get "used" to it and are able to tune it out over time to a large extent.

    Regards,
     
  7. Robert P. Jones

    Robert P. Jones Second Unit

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    The following is an answer to a question at the AVS Forum asking how the optics of the Runco DLPs compared to those of other brands, like Marantz.

    Sorry, I did not have a chance to get up close to the Runco DLP, to observe on this. From where I sat in the 3rd row, there were no observable problems, but that was pretty far away.

    Wish I had, now, but I caught myself still at the Runco booth in a basement of one of the CES buildings, as the special showing of their new products - open only to a limited number of AVS members - was starting up at 5pm, and had to rush off and get my booty to an entirely different building - The Beach, a nightspot way down and across the street from the actual show buildings - just to make the last half of the showing. We were then rushed out of this upper-story meeting room at The Beach so the press could come in - I believe the units were all turned off also, as we were leaving - for the bona-fide 6pm press release showing, which I'm sure was a repeat of the showing we had just observed, but most likely with vastly different discussions involved, between the 2 sets of observers, the press and us AVS Forum members.

    There were around half a dozen screens there, carefully set up and stretching across the room - 2 sizes of plasma, DLP RPTVs, and CRT FPTVs. Their Toshiba-based CRT RPTV was disco'd a year or 2 ago, the plasmas replacing it taking up much less space in the warehouse in Hayward, and of course needing no calibration maintenance, compared to plasmas. DLP RPTV followed soon after.

    All looked completely identical, from where I was sitting in the 3rd row, on the HD material being shown.

    At the Runco booth, I had been talking with one of the Runco guys and one of the head guys from Monster Cable about why the D-VHS VCR that Runco uses to show HD on location was screwing up during the show, in their enclosed showroom in the middle of their booth area. It kept tearing and pixellating and breaking up, during their showing of their recording of Gladiator, in HD, which was being displayed at predetermined show times on both their CRT and DLP units, one after the other, in a VERY well equipped self-enclosed room that would keep out the din of the show all around them.

    The Panasonic combo they use is connected via firewire, whose cable is wrapped around a big ferrite core on its way between connecting the one unit with the other unit - the STB and the D-VHS VCR, which evidently records the actual MPEG signal to digital or S-VHS tapes - and according to the Runco guy, had been performing flawlessly until they got it to the show and set it up. Mine performs flawlessly on playback, at my home in suburbia, until or unless a plane flies by, disturbing the UHF, as planes have always done with UHF. This disturbance only messes with the recording process, of course, not the playback process.

    It looked to me like the show, with all its incredible array of electronic devices, was causing some sort of interference in the firewire - some sort of ingress noise which was interfering with the bitstream - which was all we could come up with to explain why they were losing it on their Gladiator recording.

    I observed that the firewire connection cable, even tho impeding - via the ferrite-loaded coil - any super high, possibly superheterodyning frequencies that might be riding the cable, is essentially unshielded. They also have one ferrite-loaded set of windings each, on the 120v. power cables feeding power to each unit in that combo, BTW. Looks like superhigh frequencies really mess with the transmission of the highspeed data needed for HD, which I guess should be no great surprise...

    I asked the Monster guy about this - what is their solution? - and he said they have not done any work on shielding firewire.

    I said, "Well then, get cracking! If you guys aren't on it, you're missing the boat, as that's your field!"

    Then I looked at my watch and discovered that being in the basement of the building I was in, and the showing of Runco's new products being off campus at a nightspot, I was going to be missing the first half of the showing no matter how quickly I got outa there.

    So I said as much, shook hands with both guys, and got outa there. It only took an additional 2 minutes of talking with the bouncer at the nightspot - who didn't want to be letting me in until the official press showing at 6pm - to see that yes, I was supposed to be with the "special group" that had been let in at 5pm, and let me in to see the last half of the showing.

    Steve Brusonski, our intrepid leader of the special AVS dinner at CES, where Joe Kane hisseff appeared and spoke to the over 200 AVS members there, had extensive chats with Sam Runco about these things after our showing, where those rebadging questions had come up. I suspect he could flesh out that discussion much better than I can.

    Can anybody else answer this question, of Runco's DLP optics? Now I'd like to know, myself!

    Mr Bob
     

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