Joined: 08 Apr 2006 Posts: 7139 Location: Fort Collins, CO
Link Posted: Wed Jun 20, 2007 8:15 pm Post subject:
I'd rather you put your entire post here. The results are great. I'm glad I did it and now i know the technical reasons why
OK, if somebody is too lazy to click on the link here's the post:
Lately the color-filtered HD144 and HD145 lenses have become really popular, and for good reason. They're supposed to have better optics, better corner focus, etc., than the stock HD8b's in Marquee 8500's. More importantly (IMHO anyway), Marquees and other non-color-filtered projectors really benefit from the color filtering in these lenses. In my opinion the stock 8500's colors are very dull, very lifeless. If that's what you're used to, you may not notice a problem. But if you switch from a color-filtered projector like an NEC XG to an 8500, you'll notice a big difference. I recently put a set of HD145's in my Marquee 8500 and the improvement is dramatic.
And it turns out there's a VERY inexpensive way to try out color-filtering to see if it's worth it to you.
Unfortunately my camera is a cheap digital and can't capture the differences in colors that my eye can see. But I have a colorimeter, and I can MEASURE the difference.
Some background: the CIE diagram (below) represents the colors that the human eye can see. You can represent any of these colors with an x,y coordinate, which is what the colorimeter measures. The triangle represents the three "primaries" (red, green, blue) defined by the SMPTE C standard, which (I think) is used for North American broadcast and DVDs. It's also very close to the standards used by HDTV and PAL/SECAM.
If you want to represent an image accurately, your projector must have the SAME primaries as the standard used in your signal source -- SMPTE C if you're in North America, very close to SMPTE C elsewhere. In other words, your CRT phosphors must emit exactly the same color as the SMPTE C color. If they don't, your colors will be wrong.
Why? Think of your projector as a blind paint-by-number artist. He's got 3 pots of paint (R, G, B), and he just paints whatever color the signal tells him. If the video signal says to paint pure green, he goes to his green pot and uses that. If the signal has a yellow color, he mixes red and green together.
Now imagine what would happen if somebody swiped his green paint and substituted a pot of pink paint. He's a blind painter, so he can't correct for the bad color. Obviously his greens would be wrong; grass would be pink. But ALL colors that included any green would also be wrong. Since all colors except pure red, pure blue, and shades of pure magenta include SOME green, this means that ALL other colors will be wrong.
What about the Marquee (and Barco and similar non-color-filtered projectors)? Obviously the green tube isn't pink, but the phosphors in the CRTs don't quite match the SMPTE C standard. You may have heard of "yellowish greens and orangish reds" with the Marquees. That's why.
There's nothing you can do (tuning-wise, e.g. setting your grayscale) to change the projector's primary colors. Those are just the colors that the phosphors produce. However you CAN modify the primaries optically -- changing the color that actually hits the screen -- by putting a colored filter in the optical path. That's what the HD144's/145's do, and you can also do it with inexpensive colored gel filters.
I measured my 8500 with its stock HD8b lenses, with stock lenses & colored gels, and with color-filtered HD145's. For the "colored gel" tests I used 3 Calcolor gel filters: 4430 (light green), 4460 (med green), 4690 (dark red).
I measured the color coordinates of the primaries, which are affected only by the phosphors and the filters. I displayed a 100 IRE window and turned off the other 2 CRTs so I was measuring the pure color of a single tube. I placed the colorimeter sensor in front of the screen, pointed at the projector so the color of the screen didn't affect the measurements. (Caveat: I don't know when this Minolta TV2150 colorimeter was last calibrated. I'm hoping it's reasonably accurate.)
This picture shows the results:
As you can see, blue was already pretty close to the correct color, just a bit more "vivid" than it needs to be. That (and blue's limited light output) is why color-filtered lenses use a clear lens for blue -- it's already good enough.
Green was WAY off, in a very "yellowish" direction. The first (4430) filter moved it a bit, and the second (4460) moved it a bit more. The HD145 lens moves it almost exactly onto the SMPTE C value, just where you want it.
I was a bit surprised by the uncorrected red measurement. With all the "orangish red" comments you hear, I expected it to be above the SMPTE C point and to the left, in a really "orangish" area. To my surprise it was actually pretty close to the correct color, certainly much closer than the green. The HD145's and the red gel moved it farther out into the "intense red" area, but kept the right shade of red.
From these measurements you'd think the green is the biggest contributor to improved colors with color filtering. But it may be that our eyes are extremely sensitive to color variances in red, so the slight red error may cause more visually apparent difference than you might guess. I'm not sure. This picture (a Marquee red CRT with a red filter over one half of the tube face) sure makes it look like the filter makes a huge visual difference, even if the measurement shows a small change.
So, enough geekery, what does this look like on the screen? I found skintones to be much more lifelike. Greens and reds are much more vivid and beautiful. The opening scene of LOTR:FOTR (with Frodo reading in the woods) seemed really dull without filtering, but it's *G*R*E*E*N* and beautiful (not artificially green, just vividly alive-looking) with filtering. The Peony Pavillion scene in "House of Flying Daggers" is stunning.
My R/G primaries with color-filtered HD145 lenses:
R: .668 .330
G: .304 .588
Have you wanted to add filtered lenses to your projector, but you hesitated because of the cost? A set of HD144's or HD145's will run you somewhere around $200-250 with shipping, and you'll probably need a set of adapter plates (another $250 or so) to mount them on your projector. How do you know if it's worth it?
It's easy to find out, and very cheap. Order some Roscoe Calcolor filters. I found a place on eBay (seller jayplayer) that sold me 3 colors of filters for about $11 delivered, and that was enough to make at least 4 sets of filters. You want 4690 (Dark Red) and 4460 (Medium Green), though you may want to experiment with 4430 (Light Green) or 4660 (Medium Red) as well. Cut a piece of filter to fit on the front of your CRTs. Remove the R & G lenses, clean off the front glass of the CRTs with a good glass cleaner and a lint-free cloth, and mist a little cleaner onto the filter. Stick it onto the CRT glass and work out any bubbles. (You probably want to cover it with a tissue while you do this, so you don't get fingerprints on it.) The surface tension will keep the filter attached for a LONG time, without adding any new surfaces to increase reflections or haloes. Re-mount your lenses.
Then (**** VERY IMPORTANT ****) rebalance your grayscale to D6500 !! The colors will look TERRIBLE until you adjust your CRT for the filters. You'll have to drive your red and green a bit harder to make up for the light lost in the filters. (You'd have to do the same with the HD145's.)
But once you do, I think you'll see a dramatic difference! Pick a movie you know well that has colorful scenes. Watch it before you add the filters, and again afterwards. I'll bet you'll like the change!
If you want to go with a budget solution, you may decide to just leave the gels in there. The colors are fine, and it's dirt cheap. If you're happy with it, you've just improved your colors for almost nothing! Only problem: the gels are designed for tinting lighting, not for optical clarity. You may think the image is a bit softer, or you might notice a bit of haze in the image. If so, then you might decide the sharper HD144/145 lenses & adapters are worth the money.
(Thanks to KennyG, cmjohnson, and others for doing some of the initial research on this!)
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