Hmm, one of the mods should just make a sticky "bkchurch's inane, noob, CRT questions" so I won't keep spamming the boards with my noobish CRT questions :p . Anyway as we all know (even me) one of the biggest advantages to CRT is their deep inky blacks but I got to thinking recently after reading some stuff on the digital pj forum, how does a CRT pj produce black? I know direct view CRTs just don't scan an area that's supposed to be black (at least from what I've heard) and a DLP pj essentially just projects a very dark gray (again from what I understand) but how does a CRT pj do what it does so well?

At first I thought they did it the same way a direct view CRT does, hence why such a dark environment is required for a CRT but then someone over on the digital forum said they had a CRT that they could get as bright as their 4805 so it could cut through some ambient light and look as good as a low end digital (like say a Mits HD1000U) so then I got to thinking maybe it produced black the same way a digital does only far far better. So someone care to clarify this please? It's not really essential information but I've really started to love this whole home theater thing and it's really fun finding out how these things work so I was kind of curious. Plus my Barco 701s is 1000 lumens so I'm thinking it may be able to cut through some ambient light and produce a decent (although by no means stellar) image if necessary, but I'll find that out when I finally get it set up (hopefully this weekend).

Ok, now on to my second question which will sound even more noobish than the first: Gamma, what is it and how do I go about adjusting it (is it just in the menu somewhere?) since apparently if I crank it down I'll get even more amazing blacks. Thanks for any answers you can give me guys.

It does it the came way direct view does it and the reason you need light controled room is so that the screen does not reflect any ambiant light. this light would turn the black screen area, where no light is being reflected, to the color of that ambiant light.

Some one else with a littl more koledge chime in please especialy about gamma.

Athanasios

CRT does "scan" also black areas, but you adjust black video signal to level where it just barely makes phosphorus to light (adjusting brightness) but so little that it can't be seen in screen.

Light output of phosphorus is not linear to voltage, it follows power law (http://en.wikipedia.org/wiki/Power_law). The numerical value of that power is what we call gamma.

You can't adjust gamma in 701. If your source doesn't have gamma adjustment, your only choice is to use external device. But gamma can be fine without adjustment, that depend about how good your source and projector match.

CRT does "scan" also black areas, but you adjust black video signal to level where it just barely makes phosphorus to light (adjusting brightness) but so little that it can't be seen in screen.

Light output of phosphorus is not linear to voltage, it follows power law (http://en.wikipedia.org/wiki/Power_law). The numerical value of that power is what we call gamma.

You can't adjust gamma in 701. If your source doesn't have gamma adjustment, your only choice is to use external device. But gamma can be fine without adjustment, that depend about how good your source and projector match.

Ok, I get gamma and since I don't have any control over it (since I'm not gonna buy an external device to adjust it) but I'm still lost on black level. If it does indeed scan those black areas does that mean it is projecting black? And if so do you think a bright enough CRT (like mine at 1000 lumens) could match say a Mits HD1000U in terms of performance in low ambient light situations? I know my Barco will blow a Mits out of the water in zero light situations but I'm curious how it would stack up in a low light environment. When I say low light I pretty much mean a little sunlight seeping through around my blackout curtains.

It is not projecting black... Black, being the absence of light, is made simply by cranking down the current the electron beam is emitting so much that there is virtually no phosphor excitation, therefor little or no light output.
The reason that digitals (and film, believe it or not) produce relatively poor blacks is simply that the bulb can not be selectively turned off for a portion of the frame. Therefor the light source must be selectively occluded by the LCD (or film, or color wheel for a 1chip DLP...)

Think of the grid that controls brightness (a control signal gets sent from the set internals to the tube(s) being similar to a pin that someone is sticking in your side.

When the grid is turned off, the pin isn't sticking in your side at all, so you feel no pain, and you emit no sound. At full brightness, the pin is being forced into your stomach by a professional boxer, the pain is therefore intense, and you emit a lot of sound.


(I have no idea where that analogy came from, I'm completely sober!..;))

Think of the grid that controls brightness (a control signal gets sent from the set internals to the tube(s) being similar to a pin that someone is sticking in your side.

When the grid is turned off, the pin isn't sticking in your side at all, so you feel no pain, and you emit no sound. At full brightness, the pin is being forced into your stomach by a professional boxer, the pain is therefore intense, and you emit a lot of sound.


(I have no idea where that analogy came from, I'm completely sober!..;))




Riiiiiiigghhhht.

Waiter, I'll have what he's having!

It is not projecting black... Black, being the absence of light, is made simply by cranking down the current the electron beam is emitting so much that there is virtually no phosphor excitation, therefor little or no light output.
The reason that digitals (and film, believe it or not) produce relatively poor blacks is simply that the bulb can not be selectively turned off for a portion of the frame. Therefor the light source must be selectively occluded by the LCD (or film, or color wheel for a 1chip DLP...)

I see, so then IF I interpreted that properly then my Barco 701s though a poor performer in low light situations should still be able to handle the job as well or slightly better than a 1chip DLP such as an HD70 or HD1000U correct? It's not a terribly pressing issue I'm fretting about at the moment but if my roommate in college has a desklight on while studying or something while I am screwing off (after completing all my work of course) I just wonder if the image is gonna make me yearn for one of those so called 1chip flashlights as I believe I've heard them called once or twice around here :rolleyes: .

Btw Curt you scare the bajesus out of me man, but in a good way. I just wish I could come up with simple yet effective analogies like that.

What color are the walls? I could live with ambient light once and a while as long as it's not projecting on the screen, but if the walls are light colored then forget it...you're never going to do that CRT justice.

I might consider getting a digital since im sure size is an issue, and I don't think you're going to get very good black levels anyways, but lets hear more about the room setup.

What color are the walls? I could live with ambient light once and a while as long as it's not projecting on the screen, but if the walls are light colored then forget it...you're never going to do that CRT justice.

I might consider getting a digital since I'm sure size is an issue, and I don't think you're going to get very good black levels anyways, but lets hear more about the room setup.

Yea, the walls in my dorm are more than likely going to be concrete blocks painted bright white.

I don't get it...how are you planning to setup front projection in a dorm room? A CRT projector would take up all the floor space.

Curt. It would take so long to flush all that alcohol out of your system, I doubt you could ever be completely sober. :)

Ok, actually had another thought here. Does that mean even digital projectors that supposedly perform well with a little ambient light are still gonna look like crap because that light will be reflecting on the screen and murdering the contrast? Comparing say a Mitsu HD1000U to my Barco Data 701s which do you think would look worse? Do you think either of these could produce a good image with a little ambient light?

And NautikaL to answer your questions I've checked it out and my projector can fit comfortably in my dorm, the room is big enough and the pj is small enough.

Ok, actually had another thought here.Don't hurt yourself. :D
Does that mean even digital projectors that supposedly perform well with a little ambient light are still gonna look like crap because that light will be reflecting on the screen and murdering the contrast?Exactly.

Try this: turn off your projector. (This experiment works even if you don't have a projector yet. :)) Now look at your screen, or a piece of white paper, or something like that.

There is NO light from your projector hitting that screen/paper. That is as "black" as your picture can get. Your projector can't make it darker than it is now. If you have lights on in the room, your "black" screen isn't very black.

Now try the same experiment in the middle of the night with the lights off. Chances are the screen/paper is mighty dark now. You probably can't see it at all. :) THAT "black" is a WHOLE lot blacker than the "black" you saw with the lights on.

Now let's say your projector throws out enough light to project 15 foot-lamberts onto the screen. Let's say the "black" screen with the lights on has a brightness of about 2 ftL. And the "black" screen in the dark is really pitch dark, let's say 0.001 ftL.

So the contrast ratio for the lights-on screen is (15+2)/2 = 8.5:1. It looks really washed out. You can't see any dark details because the ambient light covers them up.

The CR for the lights-out screen is (15+.001)/.01 = 15001:1.

Now *IF* your projector is a properly-configured CRT, it should be able to go just about totally dark when the picture content goes dark, and you'll see almost all of that 15001:1 CR. But if it's a digital, it still throws a lot of light in dark scenes, so your "black" screen isn't as "black" as it was with the projector off. You lose some of the CR.

Or think of it as if it was audio. Let's say your stereo has a 10000:1 volume ratio. At a full volume=10000, your ears start to bleed. At the lowest possible volume=1, you can barely barely hear it.

Now, what happens if there's a hair dryer running in the room? You can still hear the ear-bleed stuff just fine, and it'll probably drown out the hair dryer. But anything quiet in the music is gone, totally covered up by the hair dryer.

In this audio example, the hair dryer is ambient noise, like ambient light on your screen.

Now imagine you have a crap stereo, and it's got a really loud hiss in it. Again, that hiss will cover up any quiet sounds. That hiss is like the light leak that you get in a digital projector. It keeps you from hearing the quiet sounds just like light leak in a digital projector keeps you from seeing the dark details.

Gary

QUOTE "Hmm, one of the mods should just make a sticky "bkchurch's insane"

I agree 100% with what you said above. However ,I answered your question yesterday about the barco data 701s and the HD1000U. (own both). If I was you I would buy a small projector (in4805) for your dorm and be done with it. key word....DORM

Now let's say your projector throws out enough light to project 15 foot-lamberts onto the screen. Let's say the "black" screen with the lights on has a brightness of about 2 ftL. And the "black" screen in the dark is really pitch dark, let's say 0.001 ftL.

So the contrast ratio for the lights-on screen is (15+2)/2 = 8.5:1. It looks really washed out. You can't see any dark details because the ambient light covers them up.While that is basically true, there is also the factor of the white level. If a person gets a digital that is twice as bright and a screen that is half as bright (gray) then the white is still 15 ft-lamberts for the projector and the ambient light is now 1 ft-lambert, for 16:1 CR. And then there is the issue of simultaneous CR, where if you are talking about dark details in mixed scenes, the ANSI CR factor comes into play and a person isn't getting 15k:1 in a single scene with dark details and a fair amount of bright stuff with the CRT or the digital even with no other lighting.

The main way to fight that other lighting is with a high white level (a bright projector), with or without a dark screen. This can be seen easily with 2 ft-lamberts of other lighting leading to CRs of 2:1 for a 2 ft-lambert projector to 16:1 with a 30 ft-lambert projector (assuming the same white screen). Many of the digitals (like the Panasonic AX100U) have different modes for dark room viewing and bright room viewing.

--Darin

Honestly if I were you I'd just stay away from front projection in a dorm room. Just get a rear projection DLP or even an LCD, although the DLP would be better. I have a 37" widescreen DLP for the living room and the picture is pretty good, although the fleshtones are horrid. Otherwise its nice, bright, sharp, and good enough for watching TV. Plus, I wouldn't really want a screen sitting out in a dorm for obvious reasons.

Honestly if I were you I'd just stay away from front projection in a dorm room. Just get a rear projection DLP or even an LCD, although the DLP would be better. I have a 37" widescreen DLP for the living room and the picture is pretty good, although the fleshtones are horrid. Otherwise its nice, bright, sharp, and good enough for watching TV. Plus, I wouldn't really want a screen sitting out in a dorm for obvious reasons.

I've seriously thought about it, I pretty much just wanted a big screen for me and my friends to hang out and watch movies on and it would happen to give me a big screen to play my games on. Over time I got hypnotized by the idea of a projector. I think there's a 50" Toshiba DLP available at CC for $999 right now, maybe I'll check that out. Hell if I give up all hope maybe I'll just pick up an XBR970 over on Amazon before they're gone.

Edit: I'm aware the 970 is a 34" screen btw and therefor not very big.

I'm still kinda confused though...of every college I've visited, the dorms are no where near big enough to fit a TV, let alone a 80" + screen + projector. Are you talking about a rec room in a dorm or are you in an apartment :confused:?

I'm still kinda confused though...of every college I've visited, the dorms are no where near big enough to fit a TV, let alone a 80" + screen + projector. Are you talking about a rec room in a dorm or are you in an apartment :confused:?

O yea, forgot to mention I'm shooting for a 60" screen. I know it's small for a projector but hell where else can you get a 60" screen for $425? The room is about 13'x15' so I figure I can do it. As for the screen it's gonna be a piece of Wilsonart Designer White laminate so I figure I can just roll it up and stick it in the corner since the stuff is both washable and nearly indestructible (not to mention reasonably priced) it should hold up well in a dorm. Believe it or not I did put a little thought into this before I bought it :p. Unfortunately I didn't think everything through lol.

Anyway if in fact I do end up selling it how much do you think I can get for it? I bought it for $375 plus $50 shipping but hell if I can make a profit on it why not? It's a Barco Data 701s if I've failed to mention it thus far in this thread. It's in excellent shape and nothings wrong with it, it's got 8000 hours left on the tubes, and it's got HD-145 lenses (not tinted though unfortunately).

Well there are two more problems with your plan...
1. I don't think the projector with those lenses can focus properly on a 60" screen. These lenses are meant for a 100"+ screen.

2. You can't just put up a screen and then roll it away and stick it in the corner because the next time you set it up it will be in a slightly different location. You could do this if you want to touch up convergence and maybe some optical focus every time before use.

Just get a DLP rear projection...everything will be so much simpler.

Anyway if in fact I do end up selling it how much do you think I can get for it? I bought it for $375 plus $50 shipping but hell if I can make a profit on it why not? It's a Barco Data 701s if I've failed to mention it thus far in this thread. It's in excellent shape and nothings wrong with it, it's got 8000 hours left on the tubes, and it's got HD-145 lenses (not tinted though unfortunately).

I wouldn't give you $100 for a 701. You can get a good 8" pj for under $1k. NEC PGs can be had for under $500 all day long.

BK read this video primer (http://www.extremetech.com/article2/0,1697,1752639,00.asp).




Well there are two more problems with your plan...
1. I don't think the projector with those lenses can focus properly on a 60" screen. These lenses are meant for a 100"+ screen.


Umm, no. The 145s will do a 60" wide screen.

Well there are two more problems with your plan...
1. I don't think the projector with those lenses can focus properly on a 60" screen. These lenses are meant for a 100"+ screen.

2. You can't just put up a screen and then roll it away and stick it in the corner because the next time you set it up it will be in a slightly different location. You could do this if you want to touch up convergence and maybe some optical focus every time before use.

Just get a DLP rear projection...everything will be so much simpler.


Alright, it's looking like I'll strongly consider that. Anyone have any suggestions what I should sell this thing for?

Btw if I annoy anyone with my constant seemingly simple questions I'm sorry but this stuff is really interesting to me and I'm trying to figure it out and I'm definately going to make A LOT of mistakes. Think of me as the annoying younger brother of the CRT questions who asks way too many simple questions but really means well :D. I'm actually going for my degree in communications next year with a focus in audio engineering so imagine what I'll come out of there knowing in four years haha, maybe I'll be able to learn you guys something one day :p.

I wouldn't give you $100 for a 701. You can get a good 8" pj for under $1k. NEC PGs can be had for under $500 all day long.


Really? Then how come Curt can manage to sell the same and similar projector for $500 on his site? (That's not a sarcastic remark btw it's a legitimate question). I understand Curt's a very reliable source of course but still $100 seems kind've low even for a 7".

Umm, no. The 145s will do a 60" wide screen.

Okay, I wasn't sure, but I know there are some people who have had issues properly converging and focusing a small screen.


Alright, it's looking like I'll strongly consider that. Anyone have any suggestions what I should sell this thing for?

Btw if I annoy anyone with my constant seemingly simple questions I'm sorry but this stuff is really interesting to me and I'm trying to figure it out and I'm definately going to make A LOT of mistakes. Think of me as the annoying younger brother of the CRT questions who asks way too many simple questions but really means well :D. I'm actually going for my degree in communications next year with a focus in audio engineering so imagine what I'll come out of there knowing in four years haha, maybe I'll be able to learn you guys something one day :p.

Honestly, I don't think you'd be even able to sell the 701 until after summer and I don't know if you could sell it then. By the time you go through the trouble of shipping or picking up a CRT projector you might as well have spent at least $500, and as Eric said, this buys you a PG which is far superior to a barco 701. What about setting up the 701 in your parents house for when you come back for breaks? This is what I'll have to do when I go to college...no way I'm bringing the XG with me :p.

Asking questions is fine, and you don't need a degree to learn about CRT projectors and audio and other HT areas. However, a background in engineering and physics (magnetism and electric fields) certainly helps. Just make sure you read stuff on Curt's site, especially the CRT primer.

Really? Then how come Curt can manage to sell the same and similar projector for $500 on his site? (That's not a sarcastic remark btw it's a legitimate question). I understand Curt's a very reliable source of course but still $100 seems kind've low even for a 7".

Curt is an established seller with a very high reputation. He also performs modifications on many of the projectors he sells for increased reliablity and sometimes performance. The problem is that as I stated above, if someone's in the market for a CRT projector, they might as well spend at least 500$ on a projector by the time they pay for shipping or for the time/gas to pick it up. I can only think of the 701 being sold very locally to someone who wants a backup projector. Your best bet would be to set this up at your parents place so you can use it when you're home.

Okay, I wasn't sure, but I know there are some people who have had issues properly converging and focusing a small screen.




Honestly, I don't think you'd be even able to sell the 701 until after summer and I don't know if you could sell it then. By the time you go through the trouble of shipping or picking up a CRT projector you might as well have spent at least $500, and as Eric said, this buys you a PG which is far superior to a barco 701. What about setting up the 701 in your parents house for when you come back for breaks? This is what I'll have to do when I go to college...no way I'm bringing the XG with me :p.

Asking questions is fine, and you don't need a degree to learn about CRT projectors and audio and other HT areas. However, a background in engineering and physics (magnetism and electric fields) certainly helps. Just make sure you read stuff on Curt's site, especially the CRT primer.



Curt is an established seller with a very high reputation. He also performs modifications on many of the projectors he sells for increased reliablity and sometimes performance. The problem is that as I stated above, if someone's in the market for a CRT projector, they might as well spend at least 500$ on a projector by the time they pay for shipping or for the time/gas to pick it up. I can only think of the 701 being sold very locally to someone who wants a backup projector. Your best bet would be to set this up at your parents place so you can use it when you're home.

Yea, good enough. Maybe I'll just give up on the theater in my dorm idea until I'm in my second year and can get a dorm to myself. I suppose I can always buy a 22" PC monitor and hook my 360, PS3, and Wii up to that for $300 and that'll get me HD gaming in college. Hell how often am I gonna be able to play games in college anyway, between getting straight A's and having a life finding time for that may be difficult lol.

Nobody seems to have clearly answered the second question , what is gamma??

Gamma goes back to the dawn of television , and is based on the fact that tube phosphor has a non linear response ie if you ramped up beam current in a linear fashion you wouldn't get a corresponding linear lumen output but rather a curved ramp . It would be unpractical to have gamma correction built in to every display device , so almost without exception this is done at RGB level either in the video camera or Telecine chain . Yes even your handicam has gamma correction .

I think plasmas and LCD display have to reverse the Gamma effect as they are non CRT

Nobody seems to have clearly answered the second question , what is gamma??Gamma has been adapted to serve many roles simultaneously, obscuring its original purpose. The primary considerations in the creation and calibration of displays are to minimize quantization on a lossy (8 bit) channel, to linearize the display response, and to account for the change in perception of the observer to maintain rendering intent.

Gamma correction is a signal companding process
http://brucelindbloom.com/index.html?CompandCalcHelp.html
which distorts a signal for some purpose, in this case for the purpose of counteracting (downstream) a display device's nonlinear response. Display devices typically exhibit a power-law response, gamma being the value of the power. Hence, gamma correction is an inverse (1/gamma) power-law companding process.

http://www.displaymate.com/ShootOut_Part_2.htm
In practice, the Gamma Curve (Transfer Function) for essentially all displays is so far off from the theoretical inverse of the encoding function that it is totally irrelevant. The perspective that I have taken in the entire Shoot-Out article series is that the goal is for the viewer to see an image that is identical to that seen in a studio by the creators of professionally produced content – generally the director and cinematographer or videographer. So my gold standard has been the Professional Sony Trinitron / Ikegami CRT monitors that are found in just about every production studio. Whenever I have measured the Transfer Function of these monitors it has always been a virtually perfect 2.20 power-law (straight line on a log-log graph) as far down as I measured with accurate photometers, which is below 1 percent of the luminance for Reference White

Gamma goes back to the dawn of television , and is based on the fact that tube phosphor has a non linear response The nonlinearity of a CRT is a function of the electrostatics of the cathode and the grid of an electron gun; it has nothing to do with the phosphor.

Ok, I get gamma and since I don't have any control over it (since I'm not gonna buy an external device to adjust it) but I'm still lost on black level. If it does indeed scan those black areas does that mean it is projecting black? And if so do you think a bright enough CRT (like mine at 1000 lumens) could match say a Mits HD1000U in terms of performance in low ambient light situations? I know my Barco will blow a Mits out of the water in zero light situations but I'm curious how it would stack up in a low light environment. When I say low light I pretty much mean a little sunlight seeping through around my blackout curtains.


A CRT won't come close to the ambient light performance of the HD1000U withouth miscalibrating it. A 1000 lumen CRT is PEAK WHITE lumens, not ANSI lumens. Its ANSI lumens of a 1000 peak white lumen CRT is probably 200-250 lumens.

The only way to come even close to the HD1000U in ambient light is to jack up the contrast several points and jack up the brightness (black level) to elevate absolute black.

DLP is always projecting white light for black, it's just a low enough intentity that on a large screen the light is dim enough to appear dark gray.