Home Theater Projector Selection Basics

2. Projector Type (Technology)

There is no perfect technology but each one has its positives and negatives. This can be a determining factor in selecting a projector. It is nevertheless important to figure out the higher end the unit, the more efforts are made by manufacturers to overcome the technology drawback.
As an illustration, LCD technology is known for not being the best in black level due to its operating nature. The high end Epson (UB) does not suffer from poor black level, but it is even said to rival or exceed similarly priced DLP units.
The bottom line: below information is generally speaking but is neither a universal guide to technology limitations nor works exhaustively for all models. It is just the pros and cons of each technology in general.

The main types of projectors are:
• CRT (Cathodic Ray Tube)
• LCD (Liquid Crystal Display)
• DLP (Digital light processing)
• LCoS (Liquid Crystal on Silicon)

• CRT:
This is the oldest projection technology and it works basically like our old televisions. The difference is the primary colors (Red, Green and Blue) are displayed through 3 independent CRTs coupled with a lens. Contrarily to other technologies, it does not have a single native resolution and therefore it is an excellent choice for displaying different source materials.

Pros:
- Unfixed pixel field resolution
- No screen door effect
- Best (deepest) blacks
- Long life (up to 20000 Hours or more)


Cons:
- Large and heavy (as big as a 20" TV)
- Costs much more than other technologies
- If a CRT fails all of them have to be replaced to re-establish a balanced picture.
- Precise alignment or RGB CRTs are required to avoid halos (most of the time requires a professional)

• LCD:
It is about passing a light from a bulb through transparent LCD chip(s) and then projected through a lens. This is first digital technology that was made commercially available

Pros:
- Small/compact
- More installation flexibility
- High color accuracy (3LCD)
- Low power consumption
- Bright
- Inexpensive

Cons:
- Screen door effect
- Not the best blacks
- Pixels are prone to burn-out
- Lamp replacement periodically required

• DLP:

This technology works with switching DMD (digital micro-mirror device). Available in 1 or 2 Million / unit which determines the projector resolution, these mirrors modulate the reflected light according to the incoming video signal.

Pros
- Small/compact
- No screen door effect
- Excellent color accuracy
- High Brightness and native contrast ratio
- Low power consumption

Cons:
- Rainbow effect
- Lamp replacement periodically required
- More expensive than LCD


• LCoS:

Liquid Crystal on Silicon technology can be considered as a combination between LCD and DLP technologies where liquid crystals are applied to a reflective mirror substrate.

Pros

- High pixel fill rate, no screendoor effect
- Excellent color accuracy
- No rainbow effect due to no color wheel

Cons
- Relatively lower contrast ratio
- Limited lamp life (1000-2000 Hours)

What does all that tell us? Here are some examples:

- If you don't have the necessary space or don't want to spend a fortune CRT is probably not for you.
- If you want an entry projector with acceptable black level, you may want to target a DLP projector
- If you're sensitive to rainbow effect and looking for a native 1080p projector, LCD might do….And so on, But But But, the assessment at this stage is far from being complete… keep on reading!

3. Will it work in your setup?

A fatal mistake would be to chose a projector that could not fill your screen or one that does not have the installation flexibility and result would be a distorted image.

• Zoom range:

Make sure to use a projection calculator to check if the projector will fit in your installation. A 2.0:1 zoom factor will give twice as big a picture at its widest angle than its telescopic, and therefore more placement flexibility options. That is fine with many setups, but that does not mean avoiding a 1.2:1 lens projector. Just make the maths to figure out weather it works for your setup of not
LCDs are the most flexible in this regard.

• Lens shift:

lens shift allows to throw the image up and down, left and right which enables you to place the projector anywhere within the range of shift.
Same here, LCDs are more flexible, DLPs generally do not allow more than a bit vertical lens shift.
Make sure picture alignment is made through lens shift rather than Keystoning which will likely deteriorate resolution and soften the picture. And generally speaking avoid any lens shift at all if possible in order to minimize any plausible anomalies like uneven brightness and Chromatic Aberration

4. Resolution:

Resolution is simply the no. of pixels the projector can display. I won't talk about all types of resolutions but for a practical consideration they will be limited to 1280* 720 (720p) and 1920 * 1080 (1080p) for Home theater projectors.

When budget allows, shoot for the highest resolution (it is understood the more resolution the more expensive it will be). Higher resolution embodies more detail in the picture (assuming a supporting video signal), and it reduces or eliminates screen door effect.
If you are willing to stick with THX size screen requirements, you probably need 1080p to avoid screen door effect of an LCD projector. Moreover 1080p is the resolution of Blu-ray and HD-DVD and therefore no processing (upscaling deinterlacing) needs to be done….That is a huge advantage as far as PQ is concerned.

Nevertheless resolution is not the most important criteria for picture quality, contrast ratio comes in mind first, then a 720p projectors can deliver an excellent picture for less than 1000$ assuming it has the other picture elements juce.

5. Brightness:

The perceived illumination depends on both the projector light output and the screen reflective properties. The screen can be used to raise the appearing brightness or to lower it (referred to as screen gain).
The ANSI lumen rating takes into account the quantity of light emitted by the projector, whereas Foot-Lamberts adds into consideration the screen reflective surface that will end up with what we truly see. Of course when selecting a projector, "think Foot-lamberts" otherwise may result a picture that is too bright or too dark.

Do not refer to manufacturers' brightness specification to begin with. That is not to say they are cheating or that it is not accurate. Manufacturers indicate the ultimate brightness possible regardless of picture fidelity. This can be useful for presentation projectors but not so for home theaters. Sometimes in home theaters projectors best mode(s) a light filter is applied to obtain a balance or primary colors, thus reducing light output toas little as 25% of the published lumen rating... To illustrate that, the TW-2000 has been measured to output more than its rated ANSI brightness (1600 Lumen), but in its best mode it cannot output more than 350-400 Lumens.
It is also not uncommon to see a projector rated 1000 ANSI Lumens being brighter than another rated 1500 in their best modes. Read reviews!

In a nutshell, brighter is not necessarily better, but a combination of lumen output and screen material resulting in 12-20 FL in a dark room should be fine for movies.

6. Contrast:

On/off Contrast is the Ratio in brightness between maximum white and blackest black the projector can do at all. Native Contrast ratio is IMO the most important parameter of picture quality, the greater the difference, the better. Poor native contrast is synonymous of a washed out picture. Native contrast is illustrative of intra-image contrast and it is what we actually see.
On/off contrast is associated with the used of dynamic iris. Its effect is beneficial for dark pictures where it reduces the overall brightness leading to better blacks, but not contrast ratio! Go for the highest native contrast ratio producing machine you can afford for greater enjoyment!
Note: Screen reflective properties can raise or lower the perceived brightness, but there is no way they can do anything about contrast. It can increase the overall picture brightness so that both whites and blacks will be grighter, or vice versa. The use of a "high contrast grey" screen can be helpful with some ambient light, as blacks will be blacker and will apear less washed out. It helps "fool our brain" contrast is better, but again it will do nothing in reality to the native contrast ratio itself.