[mikkelp]

Hi


Everybody talks about how important it is to increase the raster size in connection to basic setup procedure. The impression to me is that it will prolong the life of the tubes... So yesterday I took of the lenses off and filled out the tube surface according to the general guidelines. Then I looked at my picture and thought, oh, it is a bit darker than before... I thought about it and then I realized that even if you do use more phosphor, you get a bigger picture that is darker with unchanged color setup... Then I'm thinking that the only way to get a brighter picture is to crank up the contrast. Back to square one...

Why is it so important to maximize the raster? Bigger is darker, smaller is brighter. If you go big you need to crank up the contrast and you introduce more wear to the tubes, no?


Any thoughts?

 

[Bert Randolph]

Hm,


good question. If it really behaves like this, i would think that the total energy of the electron beam remains the same, regardless how wide the raster is. That would cause a brighter - but smaller - image, if the raster is small. In that case you could raise the contrast a bit when going wider without stressing the tubes more.

But I am only guessing - does anybody know for sure?


Daniel.

 

[RoBro]

Wider raster makes picture less bright. You have to move the PJ closer to the screen to get back your previous picture size, then it will be just as bright as before.

Brightness is due to the beam current that does not increase with raster widening.

Raster widening spreads the same current over more phosphor and causes less wear.

Roland

 

[mikkelp]

So I'm right in the assumption that with widening the raster you will have to crank up the contrast to get the same colors as when you had the smaller raster? Would you then have more or less wear of the tube as before when increasing the contrast to make the same colors?

 

[RoBro]

With the same throw distance as before you have to crank up contrast and the resulting wear will be the same as before, but you have a larger picture on the screen.

If you maximize the raster and move your PJ forward to get the same picture size on the screen as before you will not have to change the contrast setting, keep your picture size and brightness, but you will get less wear and so longer tube lifetime (10% more raster width will give you 20% less average beam current per phosphor area which should result in about 30% increase in tube life, and that is not negligible.

Also you will get 10% more resolution without having to tweak astig or focus...

Roland

 

[mikkelp]

Well explained Roland! Thank you. Maybe that's why some people cannot agree if having contrast at 80 is too much? For people with small raters that is to high and for people with big rasters that is a normal value... Still talking CRT

 

[igroucho]

RoBros explanation is only partially correct, or should I say that he is not correctly saying what he means:

"With the same throw distance as before you have to crank up contrast and the resulting wear will be the same as before, but you have a larger picture on the screen." He should've said: With the same TD as before and using max T-face you can ( equals: MUST!) have a larger screen but THEN OTH you will have to crank up CON. But if you use max of T-face you will have to move the pj closer to the screen (in order to display the whole resulting pic) and thus you can maintain CON-value as previous (= at least unaltered wear).

So I don't think he really proposes to crank up CON but that the shorter TD makes up for a weaker light emission.

 

[Mark_A_W]

From your other thread I think you have a NEC.


NEC's can change brightness as you play with the amplitude - bring the blanking up to the side of the image will usually fix it.

 

[Niels Nielsen]

Quote:

Originally posted by Mark_A_W From your other thread I think you have a NEC. NEC's can change brightness as you play with the amplitude - bring the blanking up to the side of the image will usually fix it.

Ups, think I forgot blanking ! Moved my projector a bit in, and raised brightness 5 steps. Noticed on "Missing" tonight that I see the phosfor area not used light up dimly under my screen.......

 

[benny]

Maximising the raster size also allows one other very important benefit -- it permits a higher vertical resolution to be used before the onset of scanline overlap. When this new resolution is optomised there should be a resultant increase of light output from the tube, provided you stay within the limits of the projectors greyscale tracking capabilities.


Cheers


Russ

 

[deronmoped]

Let me get this guy even more confused


The image area is what you are shooting for, the raster is unseen and contains the image.


When you expand the image on the face of the tube it spreads the image out so it will look dimmer, but the overall brightness is the same. A small image looks bright because the light is concentrated into a smaller area. It would be kinda like a magnifying glass, hold the magniflying glass so the light is focused it will be small and bright, as you move the magnifying out of focus the image gets bigger and dimmer.


Now Russ is getting at what you want to do. Increase the size of the image area and this will let you squeeze in more scan lines. More scan lines at the same contrast you were running before means you will have a brighter picture on the same size screen. At this point you can lower the contast to give you the same brightness as before and that will make the tubes last longer or you can run a bigger screen at the old contrast setting and still have the same tube life as you did on the smaller screen.


Say you have a flashlight with a very narrow beam. You take that flashlight and draw a line across the screen with it. One line will give you only so much brightness. Now draw 400 lines on the screen with it, the image will be of a certain brightness, (now you have just increased the amount of area of the tube you can use to draw lines) now draw 800 lines with that flash light on the same size screen. The screen should be twice as bright. And your arm just flew off into the next room


Deron.

 

[RoBro]

Disagree.

You have double the scanlines but the beam is twice as fast so the average current stays the same. Light output is a function of beam current and beam current can only increase if you increase contrast setting or brightness setting.

Roland

 

[deronmoped]

Roland


So if you change the refresh rate the brightness of the image will change?


Going form a 72Hz to a 48Hz will make the image brighter? And going from 72Hz to 120Hz will make the image dimmer?


Confused, Deron.

 

[deronmoped]

Roland


Forget what I just said, I read what you said again


The image has a certain amount of time to be drawn before it has to be redrawn with a new image, how does that work its way into the brightness of the image? Or is that have to do with flicker?


Deron.

 

[RoBro]

No

I meant if you increase the resolution while keeping the refresh rate the same as before you will not get a brighter image.

If you have 10% more scanlines then the horiz frq has to be 10% higher and the single scanlines get 10% dimmer as the beam hits them a 10% shorter time.


If you just increase the refresh rate by 10% the horiz frq has to be 10% higher as in the example before but you are hitting those same scanlines 10% more often so the overall brightness stays the same.

Roland

P.S.:

Are you now even more confused?

I am !

 

[mikkelp]

"This guy" as well

 

[mikkelp]

Hm... well I'm still not satisfied with the brightness of the picture. One thing is that if I turn the brightness over 49% the blue tube lights up and "ruins" the blacks. The problem with blue is the the Black gain setting is set to 0% so I cannot adjust it further down... What to do?


Mikkel

 

[RoBro]

Gain is for the whites. There should be a blue bias somewhere...

Roland

 

[mikkelp]

Sorry. I meant "B" is 0% in the kelvin menu for the blue tube... If it is turned over 3% background lights up...

 

[mikkelp]

No one can tell me tips for brightening up me image? If I crank up the brightness it shows the raster on screen so that is not an option. There must be something one can do... Otherwise I can just put it on the junk yard...

Mind you a movie like finding Nemo or Monsters inc works fine, but the title screen for LOTR I can barely make out the Newline logo... no matter what I crank up the dark areas light up before the middle tones get visible...

For example I cannot get to see the 2 black bars in the brightness test using the "Ultimate DVD Platinum" calibration DVD...


Any help? (And no I did not touch any pots).


Mikkel