DLP Projectors ???? (1 Viewer)

[Alex Yang]

Hi,

Can somebody explain to me about DLP? I mean how does this technology works, I've read something about "tiny" mirrors in a grid array someplace...

Thanks,

-Alex

 

[Jim_Carlson]

Every mirror is one pixel. All of the mirrors are right on top of a computer chip that angles the mirrors to shine the light on the screen or not. The light being shined on the mirrors is white but it passes threw a color wheel that has the three major colors on 1/3 of the wheel. The wheel is of course spinning so that when the light happens to be shining through red all of the mirrors that need to shine red will be on, the rest off. This happens again with green and blue. This happenes VERY fast and many times...so you get the picture.

 

[Alex Yang]

Jim,

Thanks for the explanation but what exactly makes this DLP technology so much better than let's say a standard Front projection or LCD projector?

-Alex

 

[Sean M]

The chief benefits of DLP over LCD are a lack of pixel structure (comparively at the same resolution), perfect confergence, and greater contrast and black level. Since it is a reflective technology, and not a transmissive one, the mirrors that are in the "off" position reflect light away from the direction of the projected image, instead of merely becoming polarized in order to block the light.
The biggest drawback to the technology (outside of the rainbow, or color sepration artifact) is the low light output of the projectors. Since the color wheel is sequential, only one third of the light output of the projector is being used at any given time. This can vary depending on the type of color wheel being used and how many segments it has, but the net effect is the same.
This is different from from projection technologies that use three seperate chips to produce the image (3-chip DLP, D-ILA, and LCD). To compensate, presentation manufacturers use a clear segment in the color wheel that allows all of the light through but decreases color saturation.
This is all very basic DLP info. You'll get much more detail reading some of the posts in the Digital Projector forum over at www.avsforum.com.
Hope this helps some.

 

[RAF]

Alex,

When I was considering front projectors I had narrowed it down to LCD and DLP. The DLP projectors that I am interested in, the 3 chip models (which don't have the spinning wheels or rainbow effect) were, at the time almost $40,000 so they were out of my league. I just didn't like the 1 chip DLP's, but your tastes may differ. I'm very, very happy with my Sony LCD.

I've always said that, barring some new technology (which is always a possibility), my NEXT projector would probably be a 3 Chip DLP when Moore's law brings it down to the affordable range for me. Time will tell. In the meantime the reliability and lack of maintenance (or even bulb changing) on my VW10HT after two years of use has surprised even me, so I may rethink my five year or so timetable for all this.

One never knows.

 

[Alex Yang]

RAF,

Thanks for the info!!! If price were NOT an issue, theoretically speaking the best of the best front projectors then as of right now is the 3 chip DLP units?

I now understand the technology and from everything I'm reading, this technology gives you the brightest, sharpest and the most color saturated picture out there and the best of the best LCD projectors would come in 2nd because or the "transmissive" vs. "reflected" technology?

Also, exactly HOW bad is the "rainbow" effect on the one chip models?

Thanks,

-Alex

 

[John Kotches]

I'd say that LCOS/D'ILA are the best technology -- but the pricing at present is cost prohibitive for the better D'ILA projectors. The Hitachi 5500 (1365x1024 LCOS) is under US$6K these days so that isn't too expensive. If you don't mind skipping a little bit o' the available pixels it would be a good consideration at that price point.

One thing to comment on from earlier from Sean.

The pixel structure (largest fill/greatest image to smallest) is:

LCOS: 93% fill

DLP: 88% fill

LCD: 84% fill

This ties back to visible pixel structure and the distance required for screen door effect to become invisible. The larger the fill factor the closer you can be to the screen without seeing individual pixels.

I am using an NEC LT-150 proejctor, a 4:3 DLP unit designed principally for the business market. It's loud and it has some other issues.

I've modified it with the "Guy Kuo" method: silver covering of clear segment and intercolor gaps, black velvet lining of the interior, aluminum+soot lining of light path -- all are intended to reduce stray light and increasing the contrast ratio. The overall light output is reduced, but the black levels have reduced even further, allowing for the increase of contrast ratio. Addition of a Hoya FL-D filter (the bulb has a native shift towards green and a little blue), the coloration is extremely good.

Unlike RAF, I think even 1-chip DLPs are where it's at for entry level.

Did anyone notice that JVC is introducing a 48" HD RPTV using D'ILA for an MSRP of US$2400 in the near future? That has the potential for bringing the price of D'ILA PJs down from the stratosphere to pricing levels mere mortals can afford? How so? The RPTV will use the same engine as a projector and more units sold means lower cost for the engine.

Regards,

 

[John Kotches]

Alex,
The rainbow effect is a function of a few things:

• Color wheel speed.... faster is better.
• Amount of motion on the screen.
• The individual

The newer HT projectors are using 5x color wheels (it's spinning at 2.5x speed, with 6 or 7 segment color wheel, making it effectively a 5x spin).
I've watched a few of the PJs with the 5x color wheels in demonstrations, and moved my head from side to side and up and down in an attempt to see a rainbow and never did see one.
With my LT-150 I initially saw them all the time, now that I am used to the projector my brain filters out the vast majority of them. Now I see them only occasionally -- but I can induce them by moving my head from side to side... kind of like shaking my head to indicate no.
Some are much more sensitive to rainbows than others, and you'll have to see for yourself whether you are sensitive or not.
I will warn you that once you go to FPTV, you will go into your local shop, see an RPTV and think to yourself "What a terrible, tiny picture"
Regards,

 

[RAF]

Alex,

As John and others said, the color wheel and rainbow effect is an individual thing. Some people (like myself) are bothered by it and others don't even consider it an issue. On the other hand, the three chip DLP's I saw are great (but costly.) They were using one out in LA at Fox for one of the HTF meets and I was impressed.

My mention of 3 chip DLP as being where it's "at" today was a general comment. I realize that there are other technologies out there that offer good pictures as well and I'm fairly confident that there will be even more technologies introduced by the time I'm ready for my next projector. These will either come to market at attractive pricing or drive down the cost of existing technologies.

When I was waiting (endlessly, sort of like the Outlaw 950 issue) for the release of the Sony VW10HT LCD projector I was offered a JVC DILA alternative at a competitive price. The noise of the unit, however, was so great that there was no way I would have it in my HT. You would have to build a hush box around it or place it in another room, in my estimation. In other words, it wasn't for me. (My SONY is very, very quiet in comparison.)

There are a lot of options out there right now in the FP field at a number of price points. Everyone choose what's important to him or her and takes it from there. This is, of course, not a static situation.

 

[Sean M]

I think the time for me to jump ship from CRT to a digital projector is rapidly approaching. The Sharp 9000 single chip DLP (1280x720 HD1 chip) would make me do it, if it were half the retail price it is now (no, I don't want to buy from Japan). The new HD2 chip projectors might get there, since the chips only cost half as much. I don't think that LCD or LCOS/D-ILA will have the black levels required for me to make the jump and be happy.

Alex, to give you an idea of how bad color wheel sensitivity can be (I have it REAL bad), even at 5x speed, I can still see the rainbow effect in high contrast scenes on the Sharp. The eyestrain/fatigue that I experience on normal presentation DLP's isn't there, though, so I can live with the effect. One thing I noticed, is that if I dart my eyes from left to right quickly while watching high contrast material on my CRT (usually only white letters on a black background), I can see the same effect. So I decided to stop worrying about it. I'll just drive myself crazy otherwise.

 

[Dave Getson]

http://www.dlp.com/
This site has a great video demo of how DLP technology works. Very informative!!