The least expensive type of large TV is a rear-projection LCD TV. Some projection TVs have three cathode-ray picture tubes (CRTs), which are like smaller versions of the tubes used in conventional sets. The images from those small tubes are projected onto the back of a 40 inch to 60 inch plus screen, giving them the name rear projection TV. Other rear projection TV sets use LCD, digital light processing (DLP), or liquid crystal on silicon (LCoS) technology in place of CRTs. These high tech rear projection TV sets are thinner, lighter, and as a result more expensive than comparable CRT-based sets – but they produce a higher-quality picture.
Major brands of rear projection LCD TV sets include Hitachi, Mitsubishi, Panasonic, Philips, RCA, Samsung, Sony, and Toshiba. The most popular models are HD capable, and there are three basic types of HD TVs.
So how do you choose the right rear projection LCD TV for you and your viewing needs? First, consider the space you have available before you worry about the screen size itself. Most rear projection LCD TVs have screens measuring from 42 to well over 60 inches. You might be tempted to purchase one of the biggest screens, which can span as much as 70 inches or more, but first determine how much floor space you can spare, and plan to view the TV from around 7 to 10 feet away for optimal picture quality.
Also consider depth and price. Once you know how much room you have, decide whether size or price is more important. CRT-based sets are floor-standing models with deep cabinets mounted on casters. Some take up as much space as an armchair or loveseat. Many rear projection LCD TV sets are tabletop units, or you can buy a separate stand for a few hundred dollars.
Then focus on picture quality. The best rear projection LCD TV sets deliver very good picture quality with HD content and good picture quality for DVDs and regular TV programming. Rear projection LCD TV screens provide much better picture quality than CRT models.
Also check the viewing angle. Some rear projection LCD TV sets display a better image from off-center than older sets did, which is important if your TV will be watched by several people at the same time. Before buying a particular model, see how the picture looks if you step off to the side or move up and down. With some rear projection LCD TV sets you'll see a dimmer, washed-out image as your viewing position angles away.
Once you’ve made your choice, it pays to think about whether you want an extended warranty on your rear projection LCD TV. While extended warranties may not be worth it for most products, they may be for high-priced TVs. Because rear projection LCD TV sets are expensive, check into the cost of a service plan. Find out whether in-home service is covered and whether a replacement is provided if your rear projection LCD TV can't be repaired.
Author : Linda Harrison
P R O J E C T I O N T E L E V I S I O N G U I D E S
Monday, July 9, 2007
Rear Projection LCD TV Secrets
Wednesday, July 4, 2007
Lens Flare - The Hidden Enemy Of Rear-Projection TVs
While one expects CRT-based rear projection televisions to deliver good black levels, there is a factor that can compromise black level performance in any rear-projection display.
This factor is something called lens flare. Lens flare is most commonly seen in photographs. It usually occurs when the photographer is shooting in the general direction of the sun. Bright sunlight enters the lens at an angle and bounces around inside the lens body. As it reflects off of the interior parts of the lens, some of it ends up getting on to the film, usually in the form of bright circles or shapes, broad smears of light, or lines.
Binocular, telescope, and camera lens manufacturers all try to make the inside of their optical assemblies as dark as possible and also add light baffles to try to waylay the misdirected light so that it does not spoil the image
Rear projection televisions also suffer from lens flare. The best place to see lens flare is usually during the end titles of a film. Often the titles are bright white on a black background. Look for a small single title, and pause the player at that point. Look at the black areas of the screen around the title. Is there a halo, ring , or general smear of light of the same color as the title? That unwanted light is most likely due to lens flare.
If you want to see the flare at its source, pull the screen off the TV and look into the lenses while a bright field is being displayed by the TV. Look for light being reflected off of shiny interior parts of the lens assemblies by moving your head around so you can look down into the lenses and see the insides of the lens assemblies. (Don't run your head into the mirror while trying to do this.) The light bouncing off of those interior edges and surfaces is the problem.
Your "black screen" black level very probably is quite good on your RPTV, especially if you have done the work to line the interior of the cabinet with light absorbing material, and view your TV in a darkened room. However, one small bright object on a otherwise black screen may cause light pollution on the supposedly black areas of the screen due to this problem. In images with a lot of bright areas mixed with some supposedly black areas, the black level of the supposedly black areas will suffer considerably.
Preparations for Reducing Lens Flare
CAUTION!
The following actions if performed carelessly will ruin your television. Further, lens flare can be reduced but don't expect to completely eliminate it. The cathode ray tubes which are the light source for many RPTV's emit lots of light at all angles, and it is really tough to keep some small amount of it from getting out of the lens in a direction we don't want. Expect that you'll be able to make some improvement, but you will not completely eliminate the problem.
If you do not know how to get at your lens assembly, do not consider yourself qualified to attempt this procedure. If you have butterfingers, do not even think of trying to do this. Read the whole process first, and familiarize yourself with the required steps before commencing. Scared? Good!
All of the above been said, those who are not scared off can see IF they can remove the first lens assembly. I'm going to assume you have purchased the service manual for your TV so that you know how to do this. BIG CAUTION!!!! Some lens assemblies also hold down the cover which seals in the cooling fluid that sits on top of the CRT's. The service manual will tell you about this, usually by indicating which of the screws on the CRT top cover/cap/lens assembly MUST NOT be removed. If you ignore these warnings, you could be buying a new TV. (Don't ask how I know this.)
If the lens assembly frame cannot be removed, it may still be possible to rotate the inner lens assembly to its highest position, and then pull the inner lens assembly up out of the frame. This will require the removal of the locking wingnut assembly which is used to lock the inner assembly for proper focus. Yes, that's right, you will also have to re-focus the 3 lenses after this whole job.
Find a CLEAN, WELL-LIT, UNDISTURBED place to work. No kids, pets, significant others, etc. should be able to disturb you.
Get some clean, washed cotton cloths on hand. Used White T-shirts are good choice. Clean white cotton gloves are also a good thing to have when doing this job. In addition, I highly recommend you obtain a source of clean, dry compressed air.
Examine the lens assembly. Determine how the lens assembly comes apart. In the case of the " Delta Digital 265 " lens assembly from Corning Precision Lens Inc, (This assembly is used in the Toshiba 50HDX82 RPTV, and this lens assembly is what I will refer to throughout this discussion.) the threaded screw which carries the wing nut used to lock the mechanical adjustments of focus must be removed. The end of the screw has been squared off. A small "Vise-Grip" plier can be used to gently turn this screw counterclockwise to remove it from the plastic assembly it mounts in.
Then the whole internal lens assembly can be rotated fully clockwise. Note that as you rotate this assembly that two plastic studs are turning in a couple of spiral slots to move the lens assembly up and down in the lens frame. If the lens assembly is rotated fully counterclockwise the studs will hit the end of the slot. You'll then notice that there is a groove running up the inside of the lens frame to allow those two studs to slip up inside the frame so that the inner lens assembly can be removed from or inserted into the frame. You may want to use a small hobby knife to put a bevel on the start of that groove to make it easier to push the lens assembly up out of the frame. Some gentle prying and cursing may also be necessary.
Realize that any contact with the front or rear lens while you are doing this may mean either a dirty or damaged lens. Wearing clean cotton gloves at this point is a good idea.
The lens assembly can now be disassembled by removing the screws holding the two halves together. Remove one half in such a way as to leave the lenses resting in the other half of the lens shell. Make a drawing at this point of exactly how the lenses fit into the lens shell. Which lens goes in which position, and which way does the lens face? Be sure about this, as you don't want to keep handling these lenses unnecessarily.
Note that the Corning lens assembly has glass AND plastic lenses! Glass or plastic, all of them must be handled with the utmost care. ONLY TOUCH THE EDGES OF THE LENSES, AND THEN WITH GLOVED FINGERS. The plastic lenses are shaped like cups, and thus can be safely rested on a flat clean surface with the curved side up. The center glass lens should be supported only by its edges. Some sort of cloth-lined trough of an appropriate size to support the lens should be arranged.
Now that the lenses are out of the way, you can take a look at the plastic shell that held them. In the case of the Corning assembly, the shell is molded out of black, but shiny, plastic. We want to get rid of the shine.
In addition to the shine problem, the lens retaining rings inside the lens shell may have blunt edges which also can reflect the light. Those blunt edges can be sharpened to knife edges through careful carving or through shaping with a Dremel tool. This step is time-consuming, and any burrs generated must be cleaned up, or the flare could be worsened, not made better. Afterwards, wash the shell halves thoroughly to prepare them for painting.
A high-quality flat black paint should be applied to all of the interior surfaces of the shell. (A search of the Web recently did not produce any "super" flat black paints available to us ordinary mortals. 3M Corp. used to make something nice, but they discontinued it. Arg!)
I ended up using Badger brand "Model Flex" No. 16-119 flat black paint. This is a water-based acrylic paint of good quality. It is available at better hobby shops.
Brush or spray a THIN, EVEN coat of the paint onto all of the interior surfaces of the lens shells halves. Set them aside to dry thoroughly.
Working on the Lenses
The plastic lenses in the Corning lens assembly do not have painted edges. This allows light to bounce around the inside edges of the lens and bounce back out where it should not. For painting the lenses, a top-quality small brush should be obtained at the same place where you bought the paint. The flat faces along the outer circumference of the plastic lenses, the flat outer edges of the lenses, and the outer portion of the rim of the curved face of the lenses should be painted black. As you might guess, one slip or drip could mean the purchase of a new lens assembly.
The center glass lens set in the Corning lens assembly already has some painted edges. Do not add more paint as painting the glass any more actually worsens the internal reflections from the glass lens assembly. (Don't ask how I know this, either!)
Before you start painting, put the lenses back in the shell once the paint is dry in the shell. Look through the lens assembly, particularly at the curved outer faces of the lenses. You want to identify how far in from the edge of the lens you can paint without blocking light coming through the lens assembly. I ended up painting the outer rim of the curved face of the lens on a line about 1/8th of an inch in from the circumference defined by the molded plastic retaining rings on the shell.
If you are uncertain about handling this lens painting part of the job, either skip it , or practice painting objects of the same general shape as the lenses until you feel confident. Do not load the brush heavily with paint, as this will promote paint drips running where you don't want them. This lens painting job must be done very carefully, so do not attempt it when you are rushed or distracted.
Once the paint on everything is thoroughly dry, it is time to bring out the compressed air. Blow off all dust particles and dirt from the lenses and the shell assembly halves. Use appropriate lens cleaning material and liquid to remove any fingerprints or smudges. This is another place where it is easy to scratch the lenses, particularly the plastic ones. Take your time, and think about what you're doing.
Place the lenses back in the proper order in one of the shell halves. Use the compressed air again to blow the lenses clean one more time and reassemble the shell around the lenses. Inspect the shell and lens assembly for freedom from dirt, and correct any remaining problems.
Reassemble the shell assembly back into the frame, and reinstall the screw that the focus-locking wing nut rides on. Reinstall the remaining hardware on the lens assembly. Re-inspect the entire lens assembly for cleanliness and any other problems. Correct as necessary and then set the lens assembly aside in a clean place, if you were able to safely remove the whole lens assembly.
In the Toshiba 50HDX82, the lens assembly sits atop the main CRT gun assembly. The top of the main CRT assembly just under the lens assembly consists of a cooling liquid-filled chamber with a lens molded into the top. This lens is shaped like a cup, and thus automatically gathers dust particles and dirt at the bottom, right in the main path of light going up to the lens. Use your compressed air to blow that dust out of this cup-shaped lens. The top inside rim of the cup has been blackened, but it still has a somewhat shiny finish which contributes to the lens flare.
A tremendously brave person could try to paint that blackened edge with the flat black paint we used previously on the lenses. I'm not that brave. Instead, here's what I recommend you do:
Order some black "flock paper" from Edmund Optical Supply. This paper has one side which has a light-absorbing texture. Get the thin stuff without the adhesive backing. Cut a ring-shaped piece of this flock paper. (A drawing compass is very helpful in drawing circles of the right diameter on the back of the flock paper to help as a guide for the cutting.) The outer diameter of the ring should just fit into the circular depression which surrounds the cup-shaped lens. The inner diameter of the ring should be small enough to block reflections from the edges of this "cup lens" and other off-axis light without reducing the main light beam brightness too much. I found a 5 centimeter center opening to be about right.
Use small pieces of double-sided tape attached to the back (non-flocked side) of the flock paper ring to attach it in place around the edge of the lens cup. You may want to make several trial pieces with different inside diameters for this flock paper ring before you figure out the best balance between knocking down lens flare at this point in the optical path, and reduction of screen brightness. A smaller center opening in the ring will improve the flare problem, but the main light beam can get choked off too. Another way to estimate this ring's effect is to put the lens back on over the flock paper ring, and look through the lens. If the flock paper ring is not visible through the lens once the lens is in place, go smaller on the center hole size of the ring.
Once you are satisfied with your treatment of the area underneath the main lens assembly, clean it out one more time with compressed air and reinstall the lens assembly.
Now you only have two more lenses to do, unless you have a TV with a single lens, which may be the case if your rear-projection TV is LCD, DLP, or uses some other new alphabet soup technology instead of the old-fashioned CRT's.
Lens assemblies from other manufacturers will certainly be different in detail, but the general sequence outlined above will still apply.
Conclusion and Results
It must be noted that the television on which I did this lens treatment still exhibits lens flare, it just has been reduced due to this effort. Your mileage will vary. Please look at the image below to see the difference between a treated and untreated lens assembly.
Author : Eli Aloisi
Monday, June 26, 2006
"LIGI HDTV", The New Projection TV
“LIFI HDTV”, I have never heard of this product before, but it is a very bright and beautiful LCD rear projection TV. I was not familiar with it, but it's a new model prepared for this year's CES.
The application of the new “LIFI” light source is one of its key developments; it has such a long lifespan that you no longer need to change the lamps, and it has an extremely short start-up time of 1-2 seconds. Furthermore its range of color reproducibility is 1.44 times more than the HDTV standard. In addition to this phenomenal color reproducibility, it has many other alluring specifications.
Although “LIFI HDTV” is a new line-up that has just been introduced, it certainly has joined the ranks of other alternative full high definition flat-screen TVs.
Saturday, June 17, 2006
PROJECTION TELEVISION WARNING
DO NOT USE YOUR NINTENDO WITH FRONT OR REAR PROJECTION TV
Do not use a front or rear projection television with your Nintendo Entertainment System ® (“NES”), Super Nintendo Entertainment System ® (“Super NES”), Nintendo ® 64 system (“N64”), or any NES, Super NES or N64 games. Your projection television screen may be permanently damaged if video games with stationary scenes or patterns are played on your projection television. Similar damage may occur if you place a video game on hold or pause. If you use your projection television with NES, Super NES or N64 games, neither Nintendo nor any of Nintendo’s licensees will be liable for any damage. This situation is not caused by a defect in the NES, Super NES, N64, or NES, Super NES or N64 games; other fixed or repetitive images may cause similar damage to a projection television
Monday, June 5, 2006
Rear-projection Television
Rear-projection Television
If a very large screen size is important to you, look into rear-projection televisions. These sets don't have the same size constraints as direct-view televisions because they don't use the cathode ray tube for the display. Instead, they use a projection screen. There are lots of different types of rear-projection televisions. They include:
Cathode ray tube (CRT), which uses three CRTs, one each for red, green and blue. These can produce a great picture with good contrast but can also be heavy and bulky.
Digital Light Processing (DLP), which uses one or three digital micromirror devices (DMDs) to create all of the pixels that make up the image. DLP sets also create a good picture, but gaps between the micromirrors can produce a screen door effect. Some users also notice a rainbow effect when moving their focus from one part of the screen to another in sets that use only one DMD.
Liquid Crystal Display (LCD), which directs light through liquid crystals and magnifies it for projection. An LCD TV can be lightweight and slim, but it doesn't have a good black level -- the ability to produce a true black, which is important for good detail and contrast.
Liquid Crystal on Silicon (LCoS), which is like a cross between DLP and LCD. LCoS doesn't have the screen door or rainbow effects that DLP can produce. It isn't as common as other display types, and some sets don't have a very good black level. 
Some rear-projection sets may have a smaller viewing angle than direct view sets. No matter where you sit in front of a direct-view television, the screen maintains the same picture quality. If you look at a rear-projection screen from an extreme angle, the picture may be much darker and you won't be able to see what's happening on the screen. Newer projection sets use high-quality screens that work well from most angles, but older sets may have a fairly narrow viewing area.
If you're looking to buy a rear-projection television, the main things to compare are size, resolution and screen quality. Even a top-notch picture can look muddy on a bad projection screen, so be sure to pay attention to screen material. Darker screens are better because they present an image with better light-and-dark contrast. You should also look for a screen made of glare-resistant material.