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Jeff
January 16th, 2007, 01:09 PM
I know how LCD works; HAL's screen in front of me is LCD. But how does a rear projection LCD TV work? The LCD itself is supposed to light up. What's with the rear projection? Projection on to what? Where does the "LCD" part come into the picture?

- Jeff

davidh
January 16th, 2007, 02:02 PM
I know how LCD works; HAL's screen in front of me is LCD. But how does a rear projection LCD TV work? The LCD itself is supposed to light up. What's with the rear projection? Projection on to what? Where does the "LCD" part come into the picture?

- Jeff
Years ago they used to sell transparent color LCD screens that you could lay on the horizontal glass plate of an overhead projector and attach the transparent LCD screen to a PC.

I don't know if these things are still manufactured.

I also don't know if they are related to what you are talking about.

I think I read somewhere recently about a laser projector being available in a cell phone and/or a PDA of some sort? I wonder if that idea (laser projection) is any way similar to the digital alarm clocks that project the time onto the ceiling?

DH

Dan in Saint Louis
January 16th, 2007, 02:21 PM
I know how LCD works; HAL's screen in front of me is LCD. But how does a rear projection LCD TV work? The LCD itself is supposed to light up. What's with the rear projection? Projection on to what? Where does the "LCD" part come into the picture?
The screen in front of you now probably has a fluorescent backlight shining through an LCD panel.

The projectors use a brighter light through a smaller LCD, and lenses and mirrors to expand the picture and focus it on an opaque screen (front projection) or translucent screen (rear projection).

Jeff
January 18th, 2007, 01:28 PM
The screen in front of you now probably has a fluorescent backlight shining through an LCD panel.

The projectors use a brighter light through a smaller LCD, and lenses and mirrors to expand the picture and focus it on an opaque screen (front projection) or translucent screen (rear projection).

Thanks, Dan. I understand, I think. Do you know where there might be a diagram of how rear projection LCD works? I'm thinking of a 42" Sony, but Sony's site has no such explanation.

- Jeff

Dan in Saint Louis
January 18th, 2007, 01:40 PM
Do you know where there might be a diagram of how rear projection LCD works?
Here (http://www.myhometheater.homestead.com/VideoBasics2.html) is a sketch of one using three CRTs. The LCD version would use just one lamp instead, and shine it through the LCD module to define the colors. Think of it as a slide projector but the slide is not static!

Judy G. Russell
January 18th, 2007, 10:03 PM
Thanks, Dan. I understand, I think. Do you know where there might be a diagram of how rear projection LCD works? I'm thinking of a 42" Sony, but Sony's site has no such explanation.I could swear I posted this the other day. I guess I hit cancel instead of submit. But check this (http://electronics.howstuffworks.com/projection-tv.htm) out for some diagrams and more links that may help.

Jeff
January 19th, 2007, 01:28 PM
I could swear I posted this the other day. I guess I hit cancel instead of submit. But check this (http://electronics.howstuffworks.com/projection-tv.htm) out for some diagrams and more links that may help.

Ah, good. Between Dan's site and your site I should be able to figure out how a non-notebook LCD screen works. If it is, as it appears to be, a smoke and mirrors affair I'm astounded that a box with a bunch of mirrors could be shipped with the mirrors still in focus, against a 42" or larger screen, on arrival.

- Jeff

Judy G. Russell
January 19th, 2007, 02:03 PM
Ah, good. Between Dan's site and your site I should be able to figure out how a non-notebook LCD screen works.Glad to help.

Gary Maltzen
January 19th, 2007, 05:35 PM
...I'm astounded that a box with a bunch of mirrors could be shipped with the mirrors still in focus, against a 42" or larger screen, on arrival.On my Sony (DLP) rear-projection system part of initial setup is a focussing operation where it (automatically) lines up R, B and G cross-hairs on the screen.

sidney
January 23rd, 2007, 07:56 PM
Jeff, here's another explanation of LCD projection displays (http://hometheater.about.com/cs/television/a/aarearprotv_2.htm) that goes into a bit more detail than those other two links.

-- sidney

Jeff
January 24th, 2007, 12:38 PM
Jeff, here's another explanation of LCD projection displays (http://hometheater.about.com/cs/television/a/aarearprotv_2.htm) that goes into a bit more detail than those other two links.

Thanks Sidney. Two days ago, for some reason, I got curious about the screen as turned off reflections as from windows are not reflected, but are just a blurred light source. It turns out that the screen is not glass, but is some sort of composite plastic and the fastest way to ruin it is to use Windex. In fact, it comes very close to not being able to be cleaned. Bummer.

- Jeff

James Day
January 26th, 2007, 12:44 AM
Jeff, try a drop of dish detergent in a pint of cold water; wash gently a foot square piece at a time and dry scrupulosly with several dry pieces of kitchen towel or softer dry material. It's vital that you dry completely and rapidly to avoid streaking.

You may want to consider the use of a very soft brush for normal dust removal and the washing routine only once a year.

Jeff
January 26th, 2007, 01:20 PM
Jeff, try a drop of dish detergent in a pint of cold water; wash gently a foot square piece at a time and dry scrupulosly with several dry pieces of kitchen towel or softer dry material. It's vital that you dry completely and rapidly to avoid streaking.

You may want to consider the use of a very soft brush for normal dust removal and the washing routine only once a year.

Thanks for the suggestions. Why in hell couldn't they put a thin glass plate in front of the screen? Yeah, the reflections would get worse, but I could get little fingerprints off of it with good olde Windex.

- Jeff

James Day
January 26th, 2007, 10:01 PM
Thin would be vulnerable to breakage, thick enough to not be vulnerable would be too heavy. The plastic solves both problems. Either should have an anti-reflective coating and that's what the Windex prevents from working by leaving a film on its surface. Among other thing the coating enhances contrast.