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Does your CRT hold black in presence of white?

531 Views 13 Replies 10 Participants Last post by cmjohnson, Mar 3, 2005

phil_999

Discussion Starter · Mar 3, 2005

My Vision One CRT (same as EH9501LC) does not seem to hold black in presence of white. I use an HTPC to display a pattern with a flashing white box in the middle of a black screen. When the white goes on, the black border turns to grey-ish. What is the cause of this?

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cmjohnson

· #2 · Mar 3, 2005

This may be due to your eyes doing their automatic dark adaptation thing.

The way to determine this is to put up a cardboard wall between the white

box and the rest of the screen. Position yourself so that the flashing box

is completely invisible to you, while watching the border area on your side

of the wall.

There's a really good chance that the projector is holding blacks better

than you realize.

And if it's not, the projector is worthless. Send it to me for proper disposal,

adnd I won't even charge you for it!

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darinp2

· #3 · Mar 3, 2005

Quote:

Originally posted by cmjohnson
This may be due to your eyes doing their automatic dark adaptation thing.

Actually, your eyes automatic adaptation should go the other direction. That is, make the same light level look darker when white is present next to it.

I think this effect seen is probably due to both the room and the projector. Basically, this is what ANSI CR is all about. Washout from bright parts to dark parts.
Quote:

The way to determine this is to put up a cardboard wall between the white

box and the rest of the screen. Position yourself so that the flashing box

is completely invisible to you, while watching the border area on your side

of the wall.

And what he should see is that the border will looking even brighter gray doing this while the white box is up than if his eyes were seeing the white box and adjusting to it. Or at worst be a wash.

--Darin

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garyfritz

· #4 · Mar 3, 2005

If it's equivalent to a 9501LC, it should have a mighty good ANSI CR. Have you checked the lenses? Dirty lenses can scatter a lot of light and mess up your CR.

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phil_999

Discussion Starter · #5 · Mar 3, 2005

My HD10 lens are clean. I have to try blocking off the white with a big card board and just concentrate on the black. When the white comes on, it could fool the eye.

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HoustonHoyaFan

· #6 · Mar 3, 2005

Quote:

Originally posted by cmjohnson
This may be due to your eyes doing their automatic dark adaptation thing.

CJ

Adaptation would have the opposite result. the blacks would look darker as your eyes adjusted to a brighter white.

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Mark_A_W

· #7 · Mar 3, 2005

This is just the relatively poor ANSI contrast of CRT projectors.

You choose your compromises....

(But dirty lenses will make it worse.)

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dokworm

· #8 · Mar 3, 2005

Dirty lenses, reflective (light coloured) walls, lack of screen masking and so on will make this problem worse.

CRT projectors suffer badly from this, even LC models.

If you search the threads and look for ANSI CR you will see a lot of discussion about this.

Part of the reason it happens is that the light part of the picture hits the front glass and lens assembly and some of the bright light reflects back onto the face off the crt, and light generally scatters all over the place - effectively creating a bit of ambient light in the image and washing out the black making it grey.

There is also the phosphor problem where lit phosphors cause phosphors around them to light up (This is even worse on your TV and causes 'halos).

Masking your crts and screen and making your room as light soaking as possible, cleaning the lens assembly etc. can all help - but eventually you come down to the flaws in the projector itself.

This is why in some scenes digital projectors deliver better shadow detail and better blacks than CRTs, but in all dark scenes (like a lot of AvP and Underworld and Buffy and so on) there is no bright light in scene to cause the problem, so the CRT picture has more detail.

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deronmoped

· #9 · Mar 3, 2005

This can be even caused by the cameras that the original film was shot with. The cameras that video or film was shot on are not perfect for ANSI CR, with some worse then others. After you know what to look for and start to watch movies you will see that the ANSI CR can be less, depending on the quality of the camera. I would bet the transfer process could even degrade the ANSI CR.

When it comes to a good LC PJ, the ANSI CR can for the most part look awesome, better then real life. I remember one image that I saw where there were some people about ready to go into a wharehouse, the door was open and doorway looked like what you would expect a black hole to look like! It was a real good movie, but that is what I remember the best, that super black doorway.

Deron.

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ChrisWiggles

· #10 · Mar 3, 2005

It's most likely just ANSI light spill in the room and in the projector, this is normal. As long as there is no defined streaking that is being caused by the white, then all you are seeing is spill.

You can tell if there is a problem in the projector itself by putting on some sunglasses and looking in the tubes. You will see in a tube (let's just say the green one) that the part that is the white box will be all lit up green, and the rest of the phosphor face will be lit up whitish green from the spill, but not be emitting light from the tube itself.

All displays have ANSI CR limitations. It's hard to describe what is "normal" spill on a display, and what is a display problem, however.

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draganm

· #11 · Mar 3, 2005

A vision 1 is basically a 9500LC with a fancy black case. Unlike the Sony G90, unmodified Marquee's are not known for having the greatest dynamic range. When I swapped in Mike Parker modded VIM and neck boards in my M8500, the intra-scene washout was greatly reduced because I was able to dial in the picture using a lot less contrast and Brightness than with the stock boards. My final settings using a Radeon 9600 as the source and a good Canare 25 foot cable are C-37 B-50. I have recently painted my cieling a dark color and I expect even more improvement from that after I dial everything in again.

Basically, what others are saying about ANSI CR is true, but I believe you can make a lot of improvement from where your at. In mixed scenes black areas won't be as black as they are in dark scenes, but they they should never be DLP Grey iether.

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phil_999

Discussion Starter · #12 · Mar 3, 2005

Thanks for the inputs. Sending my VIM & neck boards to Tim for upgrades are in the very near future plan. I know the VIM, but need to figure out which ones are the neck boards (are there 3 of them or only 1 neck board?)

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draganm

· #13 · Mar 3, 2005

there are 3 neck boards, 1 on each end of the tube necks

They are easy to swap on a bench, but kind of a pain on the cieling. I did mine on the cieling by swinging the rear panel up and hooking it with some wire. Then removing the 3 gold covers over the back of the tube. The neck-boards slide straight back off the tube after unplugging all the leads to it. Pay special attention to the white wire in the clocking window. There are 2 pins in the window, If you put it back on the wrong pin you won't have any G2 control and you will smoke your tube. If you have to, take a pic before unplugging anything, you can't be too careful considering how much parts and tubes cost. The only other issue is the HDM and Focus board want to drop down when uoi unscrew their cages from the rear heatsink, just be aware and secure them somehow.

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cmjohnson

· #14 · Mar 3, 2005

The truth about the white G2 wire: If you power up the projector with that lead

off its pin, the tube won't be hurt while the projector is running.

But when you power it OFF, the electron beam is sure to rake the tube face

and leave an ugly mark.

What would you do if you had the projector running and discovered that you

hadn't connected the g2 pin?

Put on a set of rubber gloves and connect the pin! I guarantee it will not do

any harm, or at the very least, it'll do far less harm than shutting down the

machine with that pin disconnected.

There are other ways you could shut the projector down safely with the G2

pin disconnected, but they're all for advanced servicemen to deal with.

The anode voltage has to be killed. Simulate a sweep failure so the HV kill

circuit kicks in. Feeling really crazy, try popping the anode leads out of the

splitter block! Maybe even yank the HVPS module out while the projector

is running, but that would probably save the tubes at the expense of

something that likely costs more!

CJ

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