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Choosing a Projector
Choosing a Projector

ducanhtran11cdth02 > 10-08-2012, 03:01 AM

Projectors provide the ultimate home theater experience. Nothing else comes as close to truly re-creating the viewing experience of a movie theater. Imagine the leathery hide of a Tyrannosaurus rex, up close and personal. Or a tight shot of Norah Jones at the piano that reveals her freckles. Picture a 240-pound linebacker barreling straight at you. Or a video game villain swinging a sword big enough to splinter your coffee table. Front-projection TV delivers all that and more — images bursting with cinematic detail and color across a larger-than-life screen measured in feet, not inches.

Enjoy your favorite TV shows, sports, and video games on a screen measuring up to 10 feet. Invite friends over for the latest Blu-ray release.
Projectors: The basics

Compact, lightweight digital projectors are making front-projection TV more practical and affordable for home theater fans.
A front-projection TV is a two-piece system: the projector and the screen. Today's digital projectors use LCD or LCoS technology. Many projectors are compact and lightweight enough to be considered portable. They're a snap to set up and use, and best of all, they're much more affordable than old CRT projectors.
You can place a digital projector on a coffee table or out of view on a bookcase, or you can mount it to the ceiling (we have custom mounts for most of the models we carry). Projector screens come in a variety of sizes, and can be free-standing, wall-mounted, or retractable (manual or motorized). Displaying images on a wall can look OK, but a screen delivers a smoother, more consistent image, and helps any projector perform at its best.
Since the image is projected onto a separate screen, everything inside a projector's compact case is dedicated to creating the sharpest, most realistic picture possible. You'll find a high-resolution imager (DLP, LCD, or LCoS), an ultra-high-intensity lamp, superb scaling circuitry, top-grade optics, and a wide selection of video inputs. What you won't find is a built-in screen or stereo speakers. Also, a projector has no built-in TV tuner of any kind, but it will display signals from an HDTV tuner, satellite receiver, or cable box.
Projectors not only deliver the largest — and some of the highest-quality — images available for home theater, they're also frequently a better value than other display types if you figure the cost per inch of screen. Most projectors can display signals from a video game console as well as a PC — it's an unbelievably engaging gaming experience. And because you're projecting an image onto a wall or separate screen, there's no glass involved, so you'll see absolutely no reflection or glare from the screen.
So pass the popcorn, dim the lights, and get ready for real home theater.
Is a projector for you?
There are a couple of key things to be aware of if you're considering a projector. First, your room lighting: for the best projector performance in a home theater, you should be able to substantially reduce or eliminate light in the room, whether it's daylight or room lights. Rooms with few windows are good candidates. If you plan to use a projector in a room that gets a lot of sunlight, you may need to limit your viewing to after dark, or consider installing blackout shades on the windows. Because of the lighting issue, projector owners generally use other TVs for some or most of their everyday viewing, and reserve the projector for "event" viewing or gaming.
Second, your viewing habits and the life of your projector's lamp: LCD and DLP projectors typically have a lamp life of 2000-4000 hours, compared to 8000 hours for digital big-screen rear-projection models. The hour rating actually represents the lamp's "half-life" — the point where its brightness has diminished by half. A lamp will still work past its half-life, but it will continue to gradually lose brightness. When you replace the lamp (it's easily user-replaceable), picture quality returns to like-new brightness. But you won't be able to simply run to the hardware store for a lamp. These projectors use special high-pressure lamps that cost between $200 and $500. Projector owners who primarily watch movies and special events run their projectors an average of about 8 hours a week. For a projector with a 2000-hour lamp, that translates to 4-5 years of use. But if you use a projector as your main TV, logging say 4 hours per day, you'll be looking at lamp replacement in under a year and a half.
Features to look for when shopping for a projector
These days, the projectors from major manufacturers all look impressive. But of course, each has its own unique strengths and weaknesses, and no single model will be the best choice for all rooms and signal sources. You can get a general idea about how a projector will perform by comparing these three key specifications.
Resolution: For digital projectors, resolution is the number of pixels measured from side to side and top to bottom of the imaging chip. High-definition projectors will have resolutions of 720p or 1080p. Projectors with greater resolution can more accurately reproduce high-resolution signals; because each pixel is smaller, images look more seamless, with less noticeable "pixel structure." A projector's built-in scaler will upconvert or downconvert all incoming signals to precisely match its "native resolution." See our article about HDTV resolution for more info.
Contrast ratio: This measures the difference between the whitest whites and the blackest blacks a projector can show. A higher contrast ratio makes it possible to display deeper blacks and more subtle color detail. Good contrast is critical for home theater projectors. In fact, many models include multiple lamp settings that let you reduce brightness and boost contrast ratio for optimum viewing in a darkened room.
Light output (brightness): Home theater projectors typically have brightness ratings of 700-2500 lumens. All projectors have plenty of brightness for watching movies in a dimly-lit or darkened room. A higher brightness rating will come in handy for viewing when there's more ambient room light. It's also helpful if you're projecting onto a wall (it's less reflective than a screen), or if you're displaying an extra-large image (110" across or larger).

Projectors have the same video inputs you find on most HDTVs, including HDMI and component video for high-def content.
Projector technologies
Many projectors today rely on one of two digital technologies: LCD and LCoS. We've outlined how they each work below.
LCD: It's not just for flat-panel TVs
You're probably familiar with flat-panel LCD screens in TVs and laptop PCs, but LCD technology also lends itself to projection displays.

The 3-panel LCD light engine of a Sony Grand Wega TV. Light from the lamp (left) passes through special "beam-splitting" mirrors. The white light is split into beams of pure red, green, and blue light. Each beam is fed through its own dedicated LCD image panel. The resulting three monochrome images are then combined to form the full-color image, which is projected through the lens.
Liquid crystals are rod-shaped molecules that bend light in response to an electric current. Each crystal acts like a shutter either passing or blocking light; the pattern of transparent and dark crystals forms the image you see.
LCD-based projectors use three high-resolution LCD image chips, one each for red, green and blue. Think of these chips as miniature flat-panel LCDs — each chip contains up to one million pixels, or more, and each pixel is driven by its own transistor and electrical conductors.
Light from the high-powered lamp is split into isolated red, green, and blue beams using special "beam-splitting" mirrors (see illustration, above). Because there's a dedicated LCD panel for each primary color, the color accuracy is excellent. Once the three single-color images are created by the LCD image chips, a prism combines them into a full-color image, which is projected through the lens.
LCoS: A more advanced form of LCD
An LCoS image chip is a complex, multi-layered design. Lots of projector manufacturers have proprietary names for their LCoS technology — for example, Sony's SXRD™. As with an LCD chip, there is a layer of liquid crystal material. But beneath that is a reflective metal layer. As the liquid crystal layer responds to the signal voltage, the molecules shift and align in corresponding patterns to create an image.
The circuitry controlling the crystals' alignment is etched into the silicon base of the chip, so it's out of the way, behind the liquid crystal layer. Light efficiency is higher because the light doesn't have to pass through the drive electronics (as it does in LCD chips). So, for a given amount of light, an LCoS panel will yield a brighter image than an LCD panel.
Most of the models currently available are the more successful 3-chip designs like Sony's SXRD projectors. 3-chip systems (both LCoS and LCD) use an elaborate light path employing "beam-splitters" that divide the light into pure red, green and blue. Each beam shines onto a dedicated image chip. Then the three monochrome images are combined by a prism to form the full-color image, which is then projected through the lens. To see how this process works, check out this short animation.
Projector placement tips
If you plan to use your projector mainly for "event viewing" — movies at night, along with the occasional sports broadcast — the simplest option is to place the projector on a table or other flat surface, and keep it stowed away in a closet or cupboard when you're not using it. Remember: a projector doesn't do sound, so to watch a Blu-ray movie, you'll need to connect your player's video output to the projector, and run the audio to your A/V receiver. And speaking of sound, if the projector will be located near you, look for a model with a quiet cooling fan.
If you have more of a dedicated home theater in mind (or if you want to keep your projector out of the reach of small children), you can ceiling-mount it. This makes for a neat, uncluttered look, but it does call for some DIY skills. We carry custom ceiling mounts for most of our projectors, so that part is straightforward. But, the projector also needs AC power, plus a video connection from any source you want to feed to it. It's not a problem for new construction, or if you're remodeling, but trickier in a finished room (especially if there's not an attic overhead). Check out our guide to in-wall wiring for installation tips.

A projector's image doesn't follow the lens precisely, like a flashlight. The image is offset a bit to accommodate placement on a table or ceiling mounting. This means that the image is raised somewhat for table placement (see above), and similarly lowered for ceiling mounting (see below). For ceiling mounting, you'll also turn the projector upside-down.

A quick look at installation considerations
As you compare projector features and performance, it's also a good idea to keep a few installation issues in mind. First, you'll want to have at least a rough idea of how large an image you want to project, because that will affect the distance between the projector and your screen. With any projector, the further you position it from your screen, the bigger the image will be. But different projectors have different "throw ratios." The throw ratio is the relationship between a projector's distance from the screen and the width of the image. A projector with a "short-throw" lens projects a larger image for a given distance from the screen, so it's a smart choice for smaller rooms where the projector is placed relatively close to the screen. Long-throw projectors are good for ceiling-mount situations where the projector will be placed further back in the room, behind the viewing position.
If your projector will be ceiling-mounted, it's important to make sure the lens is parallel to the screen. That helps ensure that your image will be true, with straight edges on all sides. If a projector isn't correctly aligned in relation to the screen, the image will look like a trapezoid instead of a rectangle — the top of the image will be wider than the bottom, or the left side will be taller than the right side, for example.
Fortunately, there are two ways to fix picture shape: lens shift and keystone correction. Lens shift lets you tweak the position of the lens inside the projector, so you can compensate for your projector being slightly off-axis. Keystone correction, on the other hand, adjusts the image's shape using internal processing that can slightly degrade the quality of the image. Nearly all projectors offer keystone correction, but only some offer lens shift. So if you'd like a little installation flexibility, especially if you plan on ceiling-mounting your projector, consider a model that offers lens shift so you can adjust the shape of the image without affecting its quality.
Finally, wherever you end up placing your projector, be sure to leave plenty of space around it to ensure proper ventilation.
A few words about screens — choosing size and type
Because it contains none of the electronics, a projection screen can be literally paper-thin. Whether your screen is free-standing, mounted to the wall, or retractable from the ceiling, it will save considerable floor space compared to a large, free-standing TV. When it comes to screen size, many people feel that bigger is automatically better. But that's not always the case. Projecting too large an image may produce a picture with less than optimum brightness, or noticeable pixel structure.
The size of the image also determines how far you should sit from the screen for optimum viewing. For an HD-capable projector, the general rule of thumb for viewing distance is 1-1/2 times the screen diagonal — so if your screen's diagonal measurement is 96" (8 feet), you would want to sit about 12 feet from the screen. Of course, viewing distance is highly subjective. After all, in a movie theater, folks naturally spread out from the front row to the back, and everywhere in between.
It's a good idea to purchase your projector before you purchase a screen — especially if this is your first experience with a front projector. Install your projector first, do some viewing just using a wall, and then decide which screen size and type best fit your needs.
All of our projectors can display both 4:3 and widescreen 16:9 material. All use an imaging device with a 16:9 "native aspect ratio," which means that all pixels display when showing widescreen signals, but showing 4:3 material causes pixels on the sides to shut off, so you'll see vertical black bars on each side. See our article about aspect ratio for more info.

The screen shot on the left shows how a projector with a native 16:9 imager displays a 4:3 image. On the right, a 16:9 image as displayed by an older 4:3 native projector.
Link bài viết: http://tinhocit.forumvi.com/t2-topic
Ps: Đổi mùi đổi vị chút cả nhà
Choosing a Projector

never.cry > 11-30-2012, 09:33 AM

trời toàn tiếng anh làm sao em hiểu
Choosing a Projector

ducanhtran11cdth02 > 12-02-2012, 11:58 AM

never.cry Đã viết:trời toàn tiếng anh làm sao em hiểu
Thì bởi rứa mới có môn tiếng Anh chuyên ngành. Mà mình cũng ngu Anh lắm huống zì là bạn
Choosing a Projector

caothuday > 12-11-2012, 10:11 AM

thì cũng phải có cả phần dịch thì mọi người mới hiểu chứ
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Choosing a Projector | Diễn Đàn Tuổi Trẻ Việt Nam Uhm.VN

Index

Choosing a Projector

Choosing a Projector

Choosing a Projector

Choosing a Projector