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Discussion Starter · #1 ·
Hi All,


Lately, I've noticed something on my XG1350 that I haven;t nocticed before, when there is a bright object on the screen, it always has a blue shadow or halo around it. It is more pronounced up and down, but is also visible to a lesser extent to the left and right. If I look through the lens, I can see it on the tube face, only on the blue tube, the red and green are clear.


Turning blue focus on and off makes no difference, and turning the contrast down to 0 also has no difference, the halo is still there.


Does anyone have any ideas?


Regards


John
 

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Hi John,


I have noticed the same "Halo" effect on my XG-1350 around bright objects. I remember reading about this here on AVS some time ago. It seems that all non liquid coupled (LC) Projectors suffer from this. That's my guess. However I could be wrong.


If you do a search on AVS for Halo, Liquid, Coulped you will see heaps of posts about it. Like this:



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Fundamentals of liquid coupling:



The reason for liquid coupling is to provide a medium for light to travel through that more closely matches the optical impedance of the lenses.


What this means is that reflections from the air/glass interface where a lens meets the air is reduced to the point where it's almost entirely eliminated.

Those reflections cause noticeable artifacts in the projected picture, most especially when a bright object is shown against a dark background in the picture. This may manifest itself as a halo of considerable size, or may appear to be a faint ghost image very near the main image, or may appear even as a faint replica of the image but at location exactly opposite the main image, 180 degrees around the rim of the CRT. A spot at 3 o'clock may have a counterpart echo at the 9 o'clock position.


Liquid coupling reduces these artifacts by acting as an impedance matching medium. Impedance is the resistance that any medium exerts against the travel of any signal through that medium. This holds true for waves in water, electrons in wire, and light in optics, too.


Where impedance changes abruptly, reflections occur. This also happens whether you're talking about sound, waves, light, or electrical impulses.


The fluid makes the change in impedance from medium to medium a less abrupt one, and hence it causes the reflections to be weaker and the transmission performance to be higher.


The optical coatings on all good quality optical devices (lenses of all kinds included) also serve exactly the same function. They are impedance matching coatings, enhancing the efficiency at which a lens transmits light and reducing reflections, which are losses.


CJ

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Taken from this thread:

http://www.avsforum.com/avs-vb/showt...hreadid=334094


Or



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If you have a pair side-by-side, then you need to take a closer look, I don't think there's anything subtle about the difference.

If you own Theatertek take a look at the white Theatertek logo against it's black background...notice how the none LC'ed unit has a rather large halo around it? Now look at the LC'ed unit, it's halo is almost non-existent. (or it should be)

It doesn't take a trained eye to see it, I had a LC'ed XG, then went to two different non-LC'ed projectors...the difference was noticeable, and I have finally gone back to an LC'ed XG...I've learned my lesson, I'll never go back.

Don't get me wrong, the XG1350 is a very good unit, and if you haven't owned an LC'ed unit, you will be very happy.

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Taken from this thread:

http://www.avsforum.com/avs-vb/showt...hreadid=247151


But there are heaps more.


Mark
 

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Hi,

just to add my $0.02 to the LC...

in an LC unit the fluid and the "C-Element" form the field flattener which is the lens nearest to the CRT in an AC lens.

Because there is no air between the tube face and the field flattener lens you get rid of 2 possible reflecting surfaces.

What counts more is that:

You get rid of the flat glas-air transition close to the tube face.

As the reflections depend on the angle the light hits the tansition, you will get the following effect on an AC unit: If you have a very small white spot, there will be a dark ring surrounding the spot and then there will be a light ring around the dark ring.

The further the transition is away from the phosphor, the wider is the diameter of the black ring.

As the transition from the c-element to the air is convex (seen from the phosphor side) it acts as a convex mirror which magnifies the dark ring, so that it ideally extends over the whole phosphor area. The light ring around the dark one will then be over the tube edge and generate no halo...

Roland
 

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It could be electronic or mechanical focus. If it is more pronounced on top and bottom the asigmation is in question. A high hour tube could also be the cause. Blue is the hardest to focus. Before making any electronic adjustments, make note of their numbers.


Chip
 

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It sounds too simple, but it really sounds like an electronic focus pot is set incorrectly. If you see it in the CRT face when peering into the blue lense, then you have an electronic focus issue. I always get tight tiny blue dots when I am done.....


Jeff in Detroit
 

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Discussion Starter · #6 ·
Hi everyone,


Thanks very much for the replies so far.


The tube has 2000 hours on it, and is unmarked. I changed it myself a little over a year ago, it is an original NEC tube.


The electronic and optical focus are as tight as can be, I checked them again today just to be sure. Optical focus is set using the phosphor grain method, and the electronic focus set using binoculars.


The problem that I am seeing is actually on the tube face, I took the lens off today just to make sure. Here is a picture directly off the tube face. Notice the halo around the words "SET UP" and "PLAY", the green and red tubes have no such halo. This happens whenever there is a bright object on a dark background. I was suspecting cabling, but normally cable problems make them selves obvious in the horizontal plane, and this problem is worse in the vertical plane, so now I'm not sure sure.



http://www.jrobbo.com/NEC/BlueHalo.jpg


Any advice is very much appreciated, and thanks again to those that have replied already


Regards


John
 

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Discussion Starter · #7 ·
Hi All,


I just did another test. I set up my laptop at the same reolution that I am running (1440 x 816 @ 75Hz), and then connected directly to the projector via a 1.5 metre breakout cable, in an effort to eliminate my cabling as the cause. As suspected, the problem still exists with the laptop.


Any help is very much appreciated


Regards


John
 

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John, the image sample is unfortunately from something without enough fine vertical detail for me to make any guesses as to what I am seeing. Also, that haloing looks more like something authored into the disc menu rather than an display artifact. Can you post close-up images from a crosshatch and a dots pattern? A vertical ghosting is very difficult to blame on cabling issue. The time constants would be far too long.


I'm wondering about astigmation and whether or not your video processor is doing some odd vertical enhancement.
 

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Discussion Starter · #9 ·
Guy,


As usual, you are 100% right, it is in fact authored onto the disk like that, and I've been chasing a red-herring.


I've noticed this effect when watching DTV on my HTPC for a little while now, but haven't been able to freeze the action in time to study it mroe closely. When I saw it on the DVD menu, I just assumed it was the same effect. I did check the DVD on my PC, but I didn't notice the effect at first, only when I turn the brightness way up.


Thanks to everyone that replied, and please accept my apologies for wasting everyones time.


Humbly yours


John
 

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I'm coming over to smack you.
 

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It's simple. Banish him with only a DVD of the Teletubbies (or a VHS recording of Oprah's 50th birthday on EP speed..:)


Curt
 

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Discussion Starter · #12 ·
Quote:
Originally posted by Mark_A_W
I'm coming over to smack you.
Have you checked with your wife to see if you're allowed out? :D
 

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Yeah, Bob's right, that's below the belt. After I've gotten permission, I'm coming over and smacking you TWICE. :D
 

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Discussion Starter · #15 ·
LOL!
 

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John,


If it make you feel any better this is a real effect with the NEC. The best (worst) example of halo is with Dory on Finding Nemo. In many of the scenes she has a distinct blue halo around her.


I just retubed a D50 and the effect is much less pronounced on that machine. It is possible that this is due to running the D50 at 576p 50Hz and the PG Xtra at 720P 75Hz. I'll try 720p 75Hz into the D50 tonight and see if the halo is as bad as the NEC.


This Halo is probably the only defect I can find in the image from the Xtra - so I guess I won't be happy now until I get a LC XG.


Aaron
 

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Quote:

If it make you feel any better this is a real effect with the NEC. The best (worst) example of halo is with Dory on Finding Nemo. In many of the scenes she has a distinct blue halo around her.



THIS IS NOT A PROBLEM WITH THE NEC!! This has been discussed in many areas. Pixar did this on purpose to simulate the optical effect of the real ocean. That is why the image looks a lot clearer in the aquarium scenes. The aquarium has filtered water so it looks very clean. The ocean is dirty, so it gives a soft haze to all the creatures. If you look real good, all the other sea creatures also seem to have this halo, especially Marlin and Dory in the scene right before they meet Bruce the shark.


On a side note. Good for Disney now that Pixar is striking out on their own. Pixar was really getting a raw deal in the negotiations.
 

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Where can John and I get our NEC machines upgraded so they show the image the way WE want it to be, not the way the disc is created.


I would have thought that with all the respect that the NEC XG and Xtra machines have, they would be capable of this level of performance. Perhap we really do need XG LC's to get that level of sophistication.


Aaron
 

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You got it wrong. A projector should only show what the film maker had in mind when creating his movie, no more, no less. If you want to see what you want to see, then getting the unit ISF color calibrated is wasting money unless you want to see the most accurate image. The NEC excels at that. NEC colors, while not perfect is a lot more accurate than the Sony VPH-G90 and Barco industrial units. If you want to get a more accurate image, you would have to pay considerably more money to get units with color corrected lenses to match the colors with the CIE chart, which usually results in a reduced brightness.
 
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