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Understanding Projector Specifications and Choosing the right Projector


Church Video Projection:

Many Churches are getting involved in large screen projection. We install motorized and manual projection screens as well as video projectors. These are often used to project songs from a computer, as well as movies from a VCR or DVD player. In an overflow area they can be used as part of a video distribution system to project the church service.

Video projectors have improved significantly in brightness, resolution and picture quality. They have also come down in price. We keep on top of the industry so that you always get the best equipment available, suited to your application and budget.

This page contains a significant amount of information. If you read through it, it will probably answer many of your questions about projectors.

Understanding Video Projector Specifications:

You are probably aware that projector brightness is measured in ANSI Lumens, but do you know what the other specifications mean, and what affect they have on performance? Here are the more common terms and their significance.

Picture Brightness:

Picture Brightness is measured in ANSI lumens. When video projectors first started to become popular, the best you could get was around 200 - 250 lumens. A few years ago, a typical decent portable projector produced about 600 ANSI lumens. Now the smallest one worth considering for portable applications is around 3000 lumens. A more typical size for installation is around 4000 - 5500 lumens.

ANSI lumens is an international standard measurement which ensures that you are comparing apples with apples when you are looking at different manufacturers. If you are using your projector on a small screen such as 6 x 8 foot, a 3000 lumen projector is usually the perfect choice, especially if it is for portable use. This will give you plenty of brightness for word projection, even with the lights on. Although you don't need to, you might want to turn the lights

For larger screens, such as 9 x 12 foot, you will find the 3000 lumen projector marginal with the lights on. You should move up to a 5000 or even 6000 Lumen projector. This handles a 9 x 12 foot screen very nicely for words with the lights on and is also great for video, especially with the lights off.

As you increase your screen size, or if you have serious problems with light, you should consider increasing your projector brightness accordingly. Now portable projectors are available up to 7000 lumens or more..

Keep in mind that when comparing lumens you are dealing with ratios. For example, an 3000 lumen projector will look 50% brighter than a 1500 lumen projector. A 5000 lumen projector will only look 30% brighter than a 3500 lumen projector, even though there is a difference of 1500 lumens in both cases. You can't really see a difference until the ratio becomes significant (assuming the contrast ratio is the same).

Contrast Ratio:

Contrast Ratio refers to the difference between the brightest part of the image and the darkest. In other words, if the contrast ratio is 400:1, this means that if part of the image is at full brightness and another part is as dark as possible, the brightest part will be 400 times brighter than the darkest part.

Contrast Ratio works hand in hand with lumens. A projector with a 1000:1 contrast ratio will look brighter than one with 400:1, even though they have the same lumen rating. This is particularly true in a darkened room. Be very careful when you are comparing projectors. Picture Brightness in lumens doesn't tell the whole story until you you combine it with Contrast Ratio.

The minimum standard for electronic theatre is 300:1 contrast Ratio. The higher the Contrast Ratio, the better your movies and pictures will look. 1000:1 looks significantly sharper.

Resolution:

LCD Projectors use three glass Liquid Crystal Display panels (red, green and blue). Light shines through these panels, through the lens and onto the screen. Each panel is divided into a number of squares (pixels). Each pixel is individually controlled to allow the proper amount of light through. The quality of the projector panels determines the contrast ratio (full on / full off). The quality also determines the thickness of the black area between the squares. The thinner the lines and the higher the contrast ratio, the better the picture looks.

Resolution refers to the number of pixels on each panel. Since these projectors are primarily designed to project computer images, the resolution value follows computer resolution standards. The typical resolution you are likely to find is XGA. This is 1024 pixels wide by 768 pixels high. XGA projectors are quite acceptable for screen sizes up to about 9 or 12 feet, at a normal viewing distance, with a computer image.

When you use a screen larger than 9 x 12, the pixels become more noticeable. An SXGA projector has a resolution of 1400 pixels wide by 1050 high. This makes the dots less noticeable. XGA resolutions are quite common for portable projectors. There are some larger projectors with SXGA and UXGA resolution.

Although higher resolution looks better, because the image appears smoother with smaller dots, it has no affect at all on how well you can see the image. This is of course unless the words are so small that the lines are smaller than a couple of pixels. If this is the case however, they will probably be too small for most people to read anyway. What higher resolution does do, is make your pictures and words look sharper, and reduce the visibility of the dots.

As projector brightness increases, generally resolution also increases. This is partly because it is assumed that a brighter projector will be used on a larger screen and therefore the resolution will become more noticeable.

One thing to keep in mind is that although computers can take advantage of higher resolution, video sources such as DVD, VCR and most Cameras can't. A video tape has a resolution of less than half that of a SVGA projector. Even high resolution cameras and DVDs don't come up to XGA resolution. Blue Ray Discs do acheive this high resolution however.

Uniformity:

This refers to the consistency of brightness over the entire image. For example, if a projector has a Uniformity of 90%, and it is projecting a pure white (or single colour) image on the entire screen there will be no more than 10% variation in intensity across the entire screen.

Better quality projectors have higher % of Uniformity, and therefore produce a more accurate image.

LCD Panel System:

This refers to the size, number and type of LCD panels the projector is using.

Number of Pixels:

This refers to the number of tiny squares which make up the projected image. The number is determined by the resolution and aspect ratio of the projector. For example, an XGA projector with an aspect ratio of 4:3 has 768,432 pixels per LCD panel making a total of 2,359,296 pixels.

Aspect Ratio:

Aspect ratio refers to the ratio of width to height of the projected image. Typical computer images are 4 units wide by 3 units high. This is also the ratio for standard television. Therefore for church applications, a 4:3 ratio is usually ideal. For home theatre on the other hand, the newer 16:9 ratio might be more desirable.

When choosing a projector, keep in mind that all projectors will handle all aspect ratios. The question is, which one will you usually be projecting. At this point in time, if it is primarily for computer projection, 4:3 is probably your best choice.

Image Size:

This refers to the minimum and maximum size image the projector is capable of projecting and still be in focus. It is not usually of concern when selecting projectors.

Throw Distance:

This is very similar to Image Size. It refers to the minimum and maximum distance within which the projector will focus.

Motorized Zoom & Focus:

This means that you can control the size of the image and focus it right from your remote control. If you don't have motorized zoom and focus, you need to actually go to the projector and manually adjust them. For a portable projector, this may not be a problem. For an ceiling mounted projector, once it is installed and adjusted, the focus and zoom don't need to be readjusted unless you want to change the image size on the screen. Sometimes this is desired however.

Zoom Ratio:

This refers to the amount of difference between the smallest image size and the largest, without moving the projector. A typical projector has a zoom ratio of 1:1.3. This means that if the smallest image for a given screen distance is 10 feet, the largest will be 13 feet.

Throw Ratio:

This is tied to the Zoom Ratio. It tells you the minimum and maximum distance the projector can be from a given size screen. The minimum distance will be (screen width x smaller number) and the maximum distance will be (screen width x larger number). For example, a projector with a Throw ratio of 1.7 - 2.2 can fill a 10 foot screen when placed between 17 feet and 22 feet from the screen.

Digital Zoom:

Digital Zoom is a feature which allows you to "zoom in" on a section of the image. If you are showing a steady computer image, you can choose a portion of the image and enlarge it. Some projectors can enlarge it up to 49 times the original size.

Freeze Frame:

This is a feature which "freezes" the projector image regardless of the projector input. When using a computer, this will lock the present image on the screen and keep it there while you do whatever you like on the computer. When you "unfreeze" the projector, it changes to whatever is then coming out of the computer.

Freeze Frame also works on Composite Video inputs. You can "freeze" the image from a Video Tape, DVD or Camera with no picture quality degradation.

No Show:

No Show, simply causes the projected image to become black. Pressing the button a second time, brings back the image.

Computer Compatibility:

This specification refers to the different computer video resolutions the projector will accept. For example an XGA projector will probably accept VGA, SVGA, XGA and SXGA. Although its native resolution is XGA, it will process the other ones internally to provide the best image possible.

Scanning Frequency:

Different computer outputs have different vertical and horizontal scanning frequencies. For example VGA (640 x 480 resolution) can be as low as 32 Hz Horizontal and 60 Hz Vertical, and SXGA can be up to 81 Hz Horizontal and 76 Hz Vertical. In order for the projector to be compatible with your computer, it must have a range which covers your requirement.

Most of the XGA projectors we sell have a Horizontal range from 15 Hz to 80 Hz and a Vertical range of 50 Hz to 100 Hz.

Dot Clock:

Dot Clock is the speed at which the information is processed to make up an image in 1/60 of a second. This specification comes from the computer's Video Card. The projector must have the ability to match the speed of the Computer Video. A VGA resolution (640 x 480 or 307,200 dots) has a significantly lower clock speed than SXGA (1280 x 1024 or 1,310,720 dots). For most XGA Video Cards, the speed is about 140 MHz and up. UXGA will require a minimum speed of 230 MHz.

Dot Clocks are downward compatible, meaning that as long as the projector's speed is higher than the computer, it will work. In terms of economics, the faster the Dot Clock speed, the higher the cost.

Power Lens Shift:

This is a pretty neat feature. Using a motor drive, the lens is actually physically shifted up and down using the remote control in order to position the image properly on the screen. If the projector is not positioned exactly at the bottom (or top for ceiling mount) of the screen, this Lens Shift feature will move the image up or down to make it square with the screen.

Some projectors have both vertical and horizontal lens shift. This means that the projector can be off axis to the screen both vertically and horizontally and the image can still be squared up.

Lens Shift corrects the picture without using Keystone Correction (which has its side affects). It also allows you to stack two similar projectors on top of each other, doubling the light output.

Up/Down & Left/Right ratio:

Up/Down ratio is the image movement possible in relation to the lens center of the projector. In the PLCXT20 this is variable due to the lens shift feature. The Up/Down ratio for the PLCXT20 is 10:0 - 1:1. It also has a Left/Right ratio of 13:7 - 7:13.

Colour System:

There are two major Video standards in the world. One is used in North America and the other is used by the rest of the world. This generally creates a problem because you can't show a European Video Tape on a North American VCR or vice-versa. The VCRs and TVs are not compatible. Fortunately, this is not true with the Video Projectors we sell. They accept PAL and NTSC as well as SECAM Colour Formats.

Rear Screen Projection:

This is a feature which reverses (mirror image) the projection so that it can be used for Rear Screen Projection. It is simply a function on the menu which you can turn On and Off.

Ceiling Mountable:

Unlike Overhead Projectors which need to be positioned in the center of the screen to give a square image, Video Projectors are designed to be even with the bottom of the screen. When a projector is ceiling mounted, obviously you don't want to locate it at the bottom of the screen, so we turn the projector upside down and position it at the top of the screen. In order for the projector to be Ceiling Mountable, it must invert the image (turn it upside down), so that we can mount the projector upside down.

Digital Progressive Scanning:

This is feature which converts interlace video signals (standard TV) into progressive scan signals in order to provide excellent picture quality.

Digital Signal Processing:

A computer's image signals are digital. In order for us to see this signal, the video card changes this digital signal to analog so it can be displayed in monitors. This analog signal is fed it to a projector (a digital processing device) where it changes the analog signal back to digital. Digital signal processing bypasses the digital to analog and analog to digital conversions. The digital to digital transfer eliminates several shortcoming i.e. image noise, signal degradation, and ghosting. However, computers must be equipped with a DVI (more popular) or DFP terminals to make this happen. Digital processing is sometimes referred to as pixel to pixel processing.


Digital Keystone Correction:

If you can position the projector exactly even with the bottom of the screen (or top for ceiling mount), you will get a perfectly square image on the screen. If you can't, you will see the wedge shaped image you are probably familiar with when you use an Overhead Projector. Most projectors now have Digital Keystone Correction. This feature processes the image inside the projector electronics to correct for the projection angle, giving you a square image. Some projectors have both Vertical and Horizontal Keystone Correction. They can be positioned off axis both vertically and horizontally relative to the screen.

This is a great feature, especially for portable use, but it does have disadvantages. A corrected image is slightly rough along the edges, although this is not very noticeable if the edges are on the black border of the screen. It also reduces the resolution of the image. It digitally compresses the portion which is being made narrow, and turns off the pixels along the edges which are not being used. The number of horizontal pixels in the narrow part of the picture is less than that of the wider part.

A projector with Lens Shift, can accomplish the same thing with no side affects.

Electronic Workstation Compatible:

This means that in addition to PC (windows based systems) and MAC computers, the projector is also compatible with Workstations such as SUN Microsystems which use different hardware and operating systems.

PC-Less Presentation:

This is an option on some projectors which allows you to plug a preprogrammed card into it. The card has the video presentation already programmed on it. The projector can then present the slide show without connecting a computer to is.

This feature might be useful for a continuous slide presentation at a trade show, or other repetitive public event, but I don't see much use for it in a Church setting.

Auto Image:

There are many different computer outputs such as VGA, SVGA, XGA, Super-XGA, MAC. The Auto Image feature enables the projector to accept any of these signals and Automatically adjust itself to project it properly.

HDTV Compatible:

The new High Definition Television format is a ratio of 16 units wide by 9 units high. Most projectors are designed to handle this as well as the standard 4:3 computer and TV ratio.

Computer Inputs:

Almost all multimedia projectors have the standard HDB-15 pin connector used for the computer's monitor output. Some projectors have two computer inputs allowing you to switch between the computers using the projector remote control. Some projectors also have other types of computer inputs such as the new DVI (Digital Video Interface) connector or RGBHV which allows you to use high quality coaxial cable to connect from the computer to the projector.

Monitor Output:

This is usually a HDB-15 connector which loops the signal coming into the projector from the computer back out of the projector. It can be used to feed the same image from one projector into another, or to a computer monitor.

Video Inputs:

Along with computer inputs, a projector also needs Composite Video inputs. This allows you to connect a VCR, DVD player or Camera into the projector.

The most common, and basic, input of course is the single Composite Video input using an RCA connector. This is usually used to connect a VCR or Camera to the projector.

The next step up is the S-VIDEO connector. This is a miniature multi pin pin connector commonly used to connect from a DVD player to the projector. The S-VIDEO connection usually offers a slightly higher quality picture depending on the cables you use, but cable length is quite limited.

The third input which some projectors have is Component Video. This consists of three RCA connectors which can again be used with some DVD players. Choosing this input and using high camera quality coaxial cable gives you the next step up in quality.

Although the higher resolution inputs can show a bit of an improvement for DVD videos, nothing beats the resolution of a DVD played through a computer using the VGA input on the projector.

USB and/or PS2 Port:

Some projectors allow you to connect a cable between the projector and the computer USB or PS2 port. This enables you to use the projector remote control to operate as a wireless computer mouse. In my experience, this only works if the interconnecting cable is short (up to about 10 feet)

Optional Lenses:

Some projectors have interchangeable lenses. The PLCXT20 for example comes with a standard medium throw lens, but you can purchase optional lenses for short or long throw. The lenses are baronet mount, so they can easily be changed back and forth.

Although extra lenses are expensive (around $2000) they allow you to operate the projector at a wide range of distances depending on your room requirements.

dB Rating:

This refers to the amount of fan noise the projector produces. Don't overlook this specification, it may be the loudest noise source you have in the room. A lower number means that the projector is quieter. Since every 3 dB is a doubling of sound, a projector with a rating of 36 dB is twice as noisy as one with a rating of 33 dB.

Generally, the larger projectors are quieter than the smaller ones.

Power Management:

Power Management is a feature which turns the projector lamp off if no video signal is present, or no button is pressed, for over 5 minutes. This can be very useful if you might forget to turn the projector off when it is not in use.

 

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