Optimizing the LT150(z) Using a Color Filter and Recalibration

Discussion in 'Archived Threads 2001-2004' started by Guy Kuo, Feb 17, 2002.

  1. Guy Kuo

    Guy Kuo Supporting Actor

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    This post pertains specifically to the NEC LT150 and NEC LT150Z DLP projectors, but much of the underlying information is applicable to other digital projectors.
    Out of the box, the NEC LT150 and its successor the LT150z have been low cost favorites for HT enthusiasts wishing for a reasonably priced entry level front projector. I picked up an LT150Z and after some experimentation have found or verified some techniques for quite massively boosting the image quality. Some of my internal mods like white segment silvering, lens aperture modification, light dump improvement, and light box blackout are probably similar to the secret mods done to the projector by KBK over at the AVS Forum, those are beyond the range of most users. Ultimately, it is possible to more than double the contrast ratio of the machine over the stock configuration, but doing everything would void the warranty.
    This does, however, leave an easy non-warranty voiding maneuver to take advantage of the full range of the DLP chip for each of the three primaries. It is possible to make an LT150 or LT150Z look more like a CRT in terms of black level, contrast and white balance using an appropriate color filter and adjustment of white balance.
    Think of the digital projector as being a set red, green and blue light valves. The state in which your projector reaches maximal contrast ratio is when each light valve is adjusted such that black makes each one go to its fully off state and white makes each one go to its fully on state. Pretty easy to understand since all three fully off means minimal light and all three fully on means maximal light. Maximal:minimal is the highest contrast ratio possible.
    The default or neutral setting of color temperature and white balance is not necessarily the setting that gets all three light valves adjusted for maximal dynamic range. You can use test pattern from AVIA to adjust each light valve so it is at maximal range (just short of clipping both black and white). So you do that to your projector first. Now you have the maximal contrast ratio possible on your projector. I will cover how that is done later.
    The color of the grayscale is now probably quite badly tinted by the native color of the projector bulb and color separation system. The trick now is to fix that tint in the grayscale by using a color filter rather than using the digital controls. Remember, that you just set the digital controls to the settings that yield maximal contrast range. Any deviation from those settings decreases contrast range since that would necessarily deviate the light valve away form either/or full off and full on for black and white. The trick is to do as much of the color correction as possible with a high quality coated optical filter. By use of a filter to perform white balance you get to use the full modulation range of the light valves AND get a good white balance.
    For NSH and UHP bulbs which have an excess of blue and green and paucity of red output, a filter which works well for correcting the excessive green and blue is a Hoya monocoated (or even better multi-coated) FLD filter (aka FL Day). One can be had from www.2filter.com for under $30. You need one at least 49 mm in diameter for the LT150(z). Yet larger is fine. Placed in front of the projection lens, the Hoya FLD filter corrects down the green and blue most of the way, so very little deviation from the ideal maximal dynamic range settings for the primaries is needed to achieve final white balance. You sacrifice a little of the contrast ratio slightly touching up the white balance electronically, but much less than doing white balance electronically. If you did it all electronically you cut the dynamic range of the green valve to almost half of its maximum capability.
    The result is a greater contrast range than if you used a bigger amount of digital adjustment to achieve good white balance. The overall light output is lowered, and this makes black blacker. The projector has plenty of light output anyway so the overall darker but higher contrast picture is considerably superior to one without a filter AND appropriate adjustment of the controls. You may initially think the image is too dim because you are used to the DLP blasting the screen. Give yourself a day to once more learn that bright = good. You learned that the first time you calibrated your display with AVIA. Most people need to learn that lesson all over again when they get a digital projector.
    As an aside, do not even consider a lower grade non-coated filter like the commonly available Tiffens. The Hoya and even higher grade B&W filters have much less light scatter and reflection. Also pick up a bottle of Formula MC lens cleaner. Nothing else I have tried leaves less residue when cleaning a coated lens or filter, but that is another story.
    So how do you set the red, green, and blue light valves for maximal dynamic range? You take advantage of the moving black and moving white bars in AVIA or Home Theater Tune-up. Those are special features for looking for signal clipping found only on those two DVDs. They can be found in multiple patterns on those discs but you could just use the ones in the basic brightness pattern and the color bar pattern.
    If you are connected via a RGB cable which you can disconnect the other two primary colors while adjusting the gain and bias for the remaining visible color. Recall that the moving black and white bars can be used to quite sensitively detect when clipping occurs. The darker black bar disappears when bottom end clips more than 1 IRE. The brighter white bar disappears if the top end clips more than 1 IRE. You adjust the controls for each primary so the darkest black bar and the brightest white bars are barely short of being clipped while viewing only that color.
    If you cannot isolate the individual primaries you can intentionally force the other two colors into clipping and that would allow you to see the changes in the remaining, unclipped color. You would write down the settings for that color, then go on to find the settings for the other colors. Once all three colors are done you go back and enter in the values you found.
    An alternative technique would be to use a 100 IRE full field pattern and a light meter. The meter needs to be absolutely immobile and could even be a solar cell and milliammeter. You would display the 100 IRE Field and then adjust each primary gain until you reach the point for each at which clicking upward on the digital control no long creates an increment in light output. The dark end you would have to do using the technique just preceding.
    If you are using an LT150, you will find the white balance controls in the advanced menu mode. First set color temperature to middle, do an initial brightness and contrast adjustment with AVIA, then go into the advanced menu mode and find the white balance controls. Once the three are adjusted for maximal range without clipping, do not change the main brightness and contrast controls any more. Put the filter in front of the projector and enjoy. You might need some very slight tweaks to white balance to get the grayscale even, but it will probably already be pretty good.
    One warning, do not just pop the filter in front of the projector without doing the readjustment of the three primary color ranges. You will be sorely disappointed and discouraged by the lazy approach since the primaries will not be at the correct levels to work with the filter.
    When done with the filter and reworked white balance, the machine will seem completely different.
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    Guy,
    I want to thank you for your work with this projector. I have read closely your posts on AVS in regard to the color wheel mod and the filter (as well as the other insane shit you've done, like the injection of RTV from a TB syringe to fill gaps in the wheel, or the purple glass inside the lamp module [which exploded]).
    http://www.avsforum.com/avs-vb/showt...hreadid=106909
    I was wondering when you'd post some details over here. I'm waiting until someone gets around to posting some pictures of the inside before I open up my LT150 and black out teh clear wheel.
    Just wondering if you could post exactly which patterns (title/ch number) to use to find the clipping level. I usually tend to use VE more often (sorry)- so I'm not 100% familiar with what is where.
    Also, do you have a direct link to the right filter on the www.2filter.com siet: I didn't nee a FLD referenced at first glance.
    Thanks for all your work on this- maybe sometime you can come over and take me to school on Video sciences since my video skills don't hold up to my audio knowledges.
     
  3. Guy Kuo

    Guy Kuo Supporting Actor

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    Yes, I started with a Cokin, then a Tiffen, and finally the Hoya. Save your money and go straight for the Hoya. By comparison the other two were much lower optical quality and it shows during ANSI contrast measurements.

    Use the Brightness and Color bar patterns in the Basic Video Test patterns section of AVIA. Those are probably the easiest to access in the "Advanced AVIA" section.

    Just to clarify about clipping the other two colors if you cannot disconnect them.

    While adjusting red, set the blue and green bias to minimum and gain to maximum to that blue and green clip. That makes the visual effect of blue and green clipping go away so you only see what is happening to red.

    While adjusting green set the blue and red bias to minimum and gain to maximum to that blue and red clip. That makes the visual effect of blue and red clipping go away so you only see what is happening to green

    While adjusting blue set the red and green bias to minimum and gain to maximum to that red and green clip. That makes the visual effect of red and green clipping go away so you only see what is happening to blue.

    Once you have done the above to figure out what the contrast and brightness (aka bias and gain) should be for each color, set them all to the settings that you found.

    The service menu mode of the LT150(z) is useful because it puts numbers under the sliders in the white balance. Just don't go changing parameters you shouldn't in service mode. To enter service mode.

    1. Press in sequence: help help help enter menu. The button presses should be about the pace that allows each next help screen to appear.

    2. A dialog box will pop up prompting for a password. Press in sequence: down up right up, enter

    3. The existing menus will now be enhanced with additional menu items until the projector is turned off

    I'm considering putting together the advanced mods into a more unified document, but that would definitely have to go into the Advanced DIY section of this board. Most of that isn't something regular users should even think of doing.
     
  4. Guy Kuo

    Guy Kuo Supporting Actor

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    You have to look under the catalog and then Hoya filters on the www.2filter.com web site. They don't take web orders any way so one may as well just call and tell them the filter spec. Just make sure it is a FL-Day (FLD) Hoya with at least a 49 mm diameter. Monocoated is okay (that's what I have), but the multicoated version would be better. There has been such a run on the FLD's since my postings at AVS that they are actually aware of what we are up to with digital projectors and have gotten in a extra shipment to keep up with demand.
    BTW, I'm not kidding about the Formula MC. It's really cheap like under $5 for a bottle and nothing will beat it under the intense scrutiny of projection light. Just don't ever clean a lens for filter unless you have to. Every cleaning means a risk of scratching. But if you have to clean, Formula MC and a microfiber cloth are the way to go.
     
  5. Guy Kuo

    Guy Kuo Supporting Actor

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    Was all the insane stuff worth it? Yes.

    Today, my wife said, " I really like this little guy."

    And that is from someone who is used to our above average CRT projector.
     
  6. Vince Maskeeper

    Vince Maskeeper Producer

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  7. John Kotches

    John Kotches Cinematographer

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    Vince,
    I'm not Guy Kuo, and I don't play him on TV [​IMG]
    I believe that Guy has not posted pictures due to liability issues...... Stupid but true, and a definite downside to living in a litigous society. Perhaps we should become a liturgical society instead [​IMG]
    Regards,
     
  8. Guy Kuo

    Guy Kuo Supporting Actor

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    John is largely right about why I'm reluctant to make things seem simple. I don't agree with keeping people safe by keeping them ignorant, so I DO discuss and describe some of my (mis)adventures. People learn and get ideas from such threads. However, the majority of people are much more readily rendered just knowledgable enough to be dangerous rather than to the point of safe understanding. Case in point is the repeated bad advice the semi-knowledgable give to newbies to fix red push by adjusting red gain. If you really know what you are doing, you'd never make that mistake.

    If I make advanced (aka difficult or dangerous) techniques appear too easy with step by step instructions, people lose their protective fear and jump off the plane before they even realize they don't know how to do it safely. That's why I tend to give enough detail so those who are already skilled can duplicate the work, but the much more numerous, overly enthusiastic klutzes don't over reach their bounds.
     
  9. Hugh M

    Hugh M Second Unit

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    Thanks Guy.
     
  10. Vince Maskeeper

    Vince Maskeeper Producer

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    Guy,

    I certainly understand your logic behind the lack of pictures-- and I read your similar explainations on AVS.

    However, on the other hand-- in the name of education I think that some photos of the things you are doing would be very helpful. While I'm sure you're right that some might be tempted to conduct unskilled modifications to their equipment, there are equal number like myself who are simply yearn to learn more about the technology and the science behind display devices.

    I am personally a visual person- and while your info and descriptions have been wonderful, I find myself frustrated as I would love to just be able to see what it is that you are doing- how these pieces and elements fit together- and why they work they way they do.

    Sometimes there is simply no substitute for a visual representation to allow someone to learn. Again, I completely understand your reluctance to provide what might be, for some, a tempting invitation down a path of projector destruction... however I would also like to make sure you know there are quite a few of us wanna-be tech geeks who seek only to understand the concepts of what you've done a little better!

    -Vince
     
  11. Matt Stryker

    Matt Stryker Screenwriter

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    Guy-

    I'm interested in using the FLD filter (we had talked about it in the short-lived FPTV forum over here), but my LT150 is in a strange mount. Is there any good way to get the filter in front of the lens on a ceiling mount?

    And thanks again for all the LT150 help/mods you've explored for both forums, I really think its convinced some that smaller DLP machines are viable FPTV contenders.

    -Matt
     
  12. Guy Kuo

    Guy Kuo Supporting Actor

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    Huey over in the other forum basically used a hose clamp around the filter and then attached the hose clamp at right angles to a bar which sits on the projector. Not super elegant, but it did the job.
     
  13. Parker Clack

    Parker Clack Schizophrenic Man
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    Guy:

    I am going to make this post a "sticky" that is it will stay at the top of this area for a couple of weeks so it doesn't just lost in the shuffle.

    Now you are making it even harder for me to stay away from picking one of these projectors up.

    Parker
     
  14. John Kotches

    John Kotches Cinematographer

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    Parker,
    Nothing beats DVDs on a really big screen! Well, that's not true. HD on a really big screen beats movies on a really big screen. And a really, really big screen beats a really big screen [​IMG]
    Seriously, given the investment it is probably the best bargain in digital Front PJs today, although the Sony VP-10HT for US$3200 isn't bad either.
    Regards,
     
  15. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    Parker, I'm in the same boat as you -- reading this thread is making me think "Bills or big-ass screen? Hmmm..." Suddenly, my 31" TV just doesn't seem like enough. First, you people make me buy an SVS and now this! [​IMG]
     
  16. Guy Kuo

    Guy Kuo Supporting Actor

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    There is no going back once you start using a front projector. With good setup and screen the image is very clear, dynamic and convincing. It also permanently reprograms your brain so that when you walk into a store and see the RPTV's on display all you can think is, "Ugh! How can anyone stand to watch such a little screen with that quality of picture?" It used to be that the steep price and learning curve of CRT setup badly restricted front projection to only the very skilled or well healed. Now, we are starting to see digital finally get good enough to produce a competitive picture but in a lower cost and much easier to set up package. The out of the box performance can be quite dismal and poor choice of screen fabric is another gotcha, but I think we'll soon see a lot more people get their feet wet and learn how to do it right. Two minutes to aim and focus a digital is a far cry from my usual 12 to 18 hours needed to fully optically and electronically set up a CRT projector.
     
  17. Jeremy Anderson

    Jeremy Anderson Screenwriter

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    So... is the NEC LT150 a good start for getting into front projection? I've got about $4000 coming in July that would MAYBE let me jump into this mess, so what else would I be looking at buying to get set up? Progressive DVD player? What kind of screen? I figure I could mount a screen so that I can use my 31" set for regular tv and then pull the screen down for DVD's, if that's possible.
     
  18. Guy Kuo

    Guy Kuo Supporting Actor

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    The NEC LT150 is actually discontinued, but occasionally avaialable as B-stock for about $2000. The current version, the LT150Z runs more and streets about $3400. I don't think I'd go so far as saying it is an ideal starter projector, but I can say that for the price it gives great performance and there is a great deal of experience with the machine among home theater enthusiasts. I would estimate that my image from the LT150Z would satisfy at least 95% of people - quite a bit better than I'd claim out of the box.

    In addition to the projector one needs to look at screen material and video processing. Your screen can start with something as simple as a flat latex painted wall for a real budget screen. There are other DIY screen possiblities. If even higher contrast and image fidelity are desired, a commercial screen like the very excellent ones from Stewart should be budgeted.

    Video processing is ideally done by a scaler which can output the native resolution of the projector. Some people opt for a home theater PC solution for a lower cost than a high quality scaler. If one is really on a tight budget, then at least a progressive scan DVD player should be used. A progressive scan player won't give as sharp and artifact free an image as a good scaler, but the image will still be enjoyable until one decides to move up to a higher level of image processing.

    Read, learn, ask questions, and don't go rushing into anything is the way to go. However, analysis paralysis means months and months of NOT enjoying an image truely worthy of being called home theater.
     
  19. Mark JM

    Mark JM Agent

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    Guy/ and all

    I am one of those scarey new guys that you speak of that is out of my league for anything but changing batteries in the remote! While researching here and at AVS I am overwhelmed at the need and or availability of professional calibration for both RP and FP units. Like most people, Im used to buying a TV, putting it on the entertainment center, plugging the cable into it and were set for the next 10 years. My question is, after the initial professional installation, will I be happy with my (150Z, VW-10, Z2700) without all of the very cool adjustments you do or do I need to have the time and desire to "tinker" with the unit from time to time?? I am guessing that most of you people in the business see things that I would never notice, so the bottom line is, is out of the box performance on these type of units "good enough for the Jones's?"

    thanks

    Mark

    PS post pics, post videos, dont worry about me, Im NOT gonna try it!!!
     
  20. Chauncey_G

    Chauncey_G Second Unit

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    Greetings, all, and thanks for such a wonderfully informative thread. Guy, you have intimidated me to the point of highly respecting the obvious amount of work you've done to optimize your projector! Like Mark, I'm new at the projector thing and have been researching my first FPTV purchase. Threads like this are fantastic, and thanks again for making your knowledge available to those that want to learn.

    I want to get the best out of whatever I end up purchasing, but am aware enough of my current limitations to not want to just dive into a lot of mods until I learn more (a lot more!:b).

    Therefore, I'd like to take Mark's question another step and ask if professional calibration of an FPTV like yours would produce these results? Or are the things you describe going above and beyond what a professional calibration will do?

    TIA
     

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