Finding the truth in CRT specs
CRT monitors suffer more than their share of misleading specifications. The good news is that if you're not picky, virtually any monitor on the market today will provide a stable, acceptable image for most applications. But if you're hard to please, beware, because it's easy to get obsessive over tiny differences in image quality.
| Terms you should know |
| CRT: a big
bell of glass with electron guns at one end and a viewing screen at the
other
Trinitron: a type of CRT developed by Sony. It differs from the standard tube types because it employs an aperture grille instead of the usual shadow mask. aperture grille: in Trinitron monitors, the aperture grille is a series of wires stretched vertically down the inside of the CRT (cathode ray tube) to mask the beams from the electron guns at the back of the tube. In other types of monitors, this function falls to a perforated metal plate called a shadow mask. shadow mask: a metal plate with holes in it that focuses the beams from the electron guns at the back of the CRT. The distance between these holes is called the dot pitch. electron gun: a CRT is made up of three electron guns that produce a stream of electrons, each of which causes a red, green, or blue phosphor to light up. Controlled by electromagnetism, the electron guns sweep across the screen, their strength varying so that a collared image is drawn. display area: the measurement taken diagonally from one corner to the opposite corner (the same way it's done for TVs). CRTs include the outer frame, or bezel (which typically adds an extra inch) in the measurement; for LCDs, the viewable screen area is measured. refresh rate: the image on your computer monitor doesn't just appear fully formed on the screen's phosphors: it's drawn line by line with beams fired from three electron guns at the back of the CRT. The frequency at which they redraw the image is called the refresh rate, measured in hertz. |
Another crucial non-numerical issue: the shape of the screen. You might consider paying extra for a so-called flat-flat or true-flat CRT. A flat screen drastically cuts glare, the enemy of comfortable viewing. "Flat-square" CRTs actually have a slight curvature--but they're often brighter and slightly sharper around the edges of the screen than perfectly flat screens. Again, let your eyes be the judge.
Now, the numbers. Remember the old cliché, "Lies, damn lies, and statistics"? Keep it in mind as you ponder the monitor specs salespeople throw at you:
Resolution. Higher resolution means sharper images, right? True, but at maximum resolution, most CRT monitors shrink Windows text, buttons, and bars to the point where they're too small to view or click comfortably, and the refresh rate may slip to the point where flicker becomes irritating. This table shows the optimum resolutions for three popular monitor sizes.
Any monitor worth considering should be able to produce these resolutions at a refresh rate of 75Hz or higher, which these days includes nearly every monitor sold. So, for most of us, more is just wasted capacity and expense. The exception: CAD/CAE users and graphic artists who need exceptionally crisp, fine lines.
Dot pitch. DisplayMate Technologies, which develops the leading monitor-testing software, refers to dot-pitch promotion as "the great dot-pitch swindle." Dot pitch, measured in fractions of a millimetre--typically from 0.20 to 0.28mm--most commonly refers to the distance between any two dots of the same colour (triads of red, green, and blue phosphor dots make up the pixels that form a CRT image). Theoretically, smaller dot pitches mean crisper images. But vagaries in how manufacturers measure dot pitch mean you can't rely on this number for CRT comparisons. The rule of thumb: Avoid 17-inch monitors coarser than 0.28mm and 19-inch monitors coarser than 0.26mm. Also, graphics pros should consider a CRT with a 0.20mm or 0.22mm dot pitch, because this indicates a CRT that uses Enhanced Dot Pitch technology, which produces exceptionally clean vertical lines.
Viewable screen area. The viewable area of CRT monitors measures slightly smaller than the advertised diagonal CRT size; a 19-inch CRT, for example, generally gives you an 18-inch screen area (because the measurement includes the plastic casing around the outside of the screen, called a bezel, or frame). But picky buyers should check this number carefully; some monitors vary by as much as an inch and a half.
Horizontal scanning frequency. This key number, measured in Kilohertz (KHz), indicates how high you can push the refresh rate at any resolution. Some people are highly sensitive to flicker, so watch the horizontal scanning frequency if you crave a rock-solid image; an 85Hz refresh rate should be enough for anyone. Here are the horizontal scan rates necessary to achieve 85Hz at the following resolutions:
In rare cases, a monitor won't run at an 85Hz refresh rate even if the horizontal scanning frequency is high enough to support it. The moral: if you care about higher-than-normal refresh rates, double-check the specs to make sure that the manufacturer explicitly supports the refresh rate you want at the resolution you'll be using. And the vertical scan frequency that's always listed next to the horizontal scan frequency range? That's just another way of saying refresh rate.
Warranty. Anything less than three years is suspect. Three is the norm; some manufacturers offer up to five years. The warranty should cover parts for the entire period and labour for at least the first year. Also, look for a 30-day money-back guarantee (with no restocking charge) to cover the off chance that you'll get caught with a lemon.
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