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Thursday, March 1, 2007

Digital Projectors For Photographers

Show off your images using the latest in projection technology

digital projectors - mitsubishi
Mitsubishi PK20 Pocket Projector

We may still call our multimedia productions "slideshows," but there’s no way anyone will ever confuse one of today’s digital projectors with the slide projectors of yesteryear. Compared to their analog ancestors, they’re quieter, brighter and more versatile—they’re also more expensive, so here’s what you need to know to prepare for your foray into the world of digital projectors.

Projector Types

There are three main types of digital projectors based on how the image is formed and projected. Two use a reflected-light system, the other uses transmitted light.

Digital Light Processing, or DLP, is a reflected-light system built upon an optical semiconductor known as a Digital Micro-Mirror Device. The DMM consists of an arrangement of mirrors, each of which is less than one-fifth the width of a human hair. Each mirror represents one single pixel. A projector with native resolution of 800 x 600, for example, employs 480,000 tiny mirrors.

White light passing through a color filter wheel falls on the DLP chip as red, green and blue light. Each mirror is controlled electronically to regulate how long it’s on or off, as well as the amount of each color of light that’s reflected into the lens and, subsequently, on the screen. This happens so fast that human eyes perceive a full-color image.

DLP mirrors are spaced less than one micron apart, and that minimizes the gaps between the pixels in the projected image. The result is an image that’s virtually seamless and looks sharp and bright at almost any size.

LCD projectors offer certain advantages when compared to DLP projector models with identical specifications. The main advantage is potentially better control over colors. LCD projectors are said to have superior sharpness and better color saturation. On the other hand, LCD models are sometimes weak when reproducing true blacks (and even dark grays).

LCD projectors denoted as LCDx3 (or 3LCD) indicates that they use three separate LCD panels to produce the color image. The three panels represent red, green or blue light, respectively. Light is projected through the panels and into the lens to form the image. Because of this fixed arrangement, LCD projectors are generally considered to have zero geometric distortion (at native resolution) and excellent sharpness.

digital projectors - casio
Casio XJ-S30

DLP and LCD projectors have been competing against each other for years, so which technology is superior? As with all competing standards, each has advantages and disadvantages. Bottom line: Proponents of both technologies have been striving to overcome every shortcoming, so a generic comparison is futile—each continues to improve. Not all brands of LCD or DLP projectors perform the same; the differences are subjective. If possible, evaluate the image that’s projected by the projector of your choice under typical conditions before you buy.

LCOS is a third technology that was largely ignored until recently. LCOS, or Liquid Crystal on Silicon, is moving into the spotlight because Canon engineers have leveraged its advantages while eliminating its major shortcomings. LCOS is a reflective system like DLP and offers a high fill factor, fully saturated colors and zero aberrations. On the downside, LCOS projectors are larger and still more costly. But as you’ll read in the description of the Canon REALiS X600, LCOS just might end up being the best projection technology of all.

Resolution And Brightness

Native resolution refers to the actual physical pixel count. A projector that provides SVGA resolution has 480,000 usable pixels arranged in an array that measures 800 x 600. Maximum resolution indicates the highest resolution a projector can provide. To achieve maximum resolution greater than native resolution, the image is electronically compressed. This compression can have a detrimental effect on image quality; the degree depends on the machine. It’s something you must judge for yourself.

SVGA is just sufficient to properly display digital image files. VGA (640 x 480) is definitely not a good choice. If it’s within your budget, consider stepping up to XGA (1024 x 768). You’ll get 60 percent more pixels. SXGA (1280 x 1024) is the best yet, but it’s costly.


digital projectors - epsonEpson PowerLite 76c

The larger the projected image or the closer you (and your audience) are to the screen, the more resolution you need. A question often arises as to how this compares to 35mm projectors, but unfortunately, a direct comparison isn't simple because brightness has a strong impact on how people react to the images. In some presentations in which both a 35mm projector and a digital projector were used, we noticed attendees preferred the digital projection because of the brightness.

Resolution isn’t a simple issue, however, as which size is best is somewhat dependent on the viewing distance.

Brightness is measured in lumens. This specification is generally denoted as ANSI lumens to signify that the light output was measured according to the testing procedure established by the American National Standards Institute. Brightness ranges from 1000 to 2000 for most, with the higher number becoming more standard. The advantages of a brighter projector include the ability to overpower ambient room light. For low-ambient or true lights-out productions, you may find that a 1000 to 1500 lumens rating is sufficient. If you project from the back of a big room, you’ll want a 2000 lumens projector.


digital projectors - sanyo
Sanyo PLC-XU48

Contrast Ratio

This specification indicates the projector’s dynamic range, but be careful. There are two ways to measure the contrast ratio. The so-called full on/off method measures the ratio of light output between an all-white (full-on) image and an all-black (full-off) image. This yields a higher number than the ANSI method and therefore is used by most manufacturers. For DLP projectors, look for a contrast ratio of about 2000:1. For LCDs, 300:1 to 500:1 is standard—higher is better.



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