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Choosing a Computer Monitor - The Finer PointsMay 31 '01 (Updated Aug 04 '01) Write an essay on this topic.The Bottom Line Don't be confused by manufacturers' terminology tricks. Remember that dot pitch is not supremely important. Use this information to make an informed decision. You will be happy you did. There are numerous pieces of information that monitor manufacturers won't tell you about their products. Sometimes they manipulate their specifications so their products look better than they actually are. And sometimes there are unexpected 'features' on monitors that they won't tell you about even though you should ideally be aware of them. Within this text, you'll find some information which can help you make a decision once you've narrowed your monitor short-list to a small number of CRT displays. Note: This only applies to CRT monitors (i.e. the big cumbersome ones that take up a lot of desk space.) It does not apply to LCD (a.k.a. flat-panel) displays or plasma screens. The Real Deal With Dot Pitch A lot of people want to make easy decisions and only consider a few factors when choosing a monitor. They inflate these factors' importance completely out of proportion. One of these factors is dot pitch. The manufacturers have sensed the misplaced emphasis on this figure and now play games with the numbers. In CRT monitors, the picture is made up of phosphors that are made to glow by means of a scanning electron beam. There are triads of red, green and blue phosphors that are stimulated very precisely to create colours of different intensities. The dot pitch measures the distance from one phosphor to the one of the same colour in the adjacent triad. Smaller dot pitch is better because it allows for a sharper image. But there are many interpretations of dot pitch, and the number quoted can be used to mislead the customer as to the quality of the display they are looking at. Horizontal vs. Vertical Dot Pitch - The distance from phosphor to phosphor is usually not the same when measured vertically as opposed to horizontally. The horizontal dot pitch is usually larger than the vertical one. Beware! Sometimes manufacturers will try to mislead you by quoting the vertical (V) dot pitch and hoping that you'll compare it to the larger horizontal (H) dot pitch that's often quoted by other manufacturers. The H and V dot pitches cannot be compared directly. You should find out the horizontal value for each monitor and then do the comparison. This information is often available on the manufacturer's web site in an Adobe Acrobat PDF information file or on a specifications web page. Grille Pitch & Stripe Pitch - This is also known as "dot pitch (AG)" or "aperture grille pitch." To ensure that the electron beam reaches the appropriate phosphor, monitors usually employ technologies such as shadow masks, invar shadow masks and aperture grilles (more on these later.) Essentially, these devices have a dot pitch of their own which is less than the "real" dot pitch of the monitor. If the dot pitch is listed as one of these types, the "real" number is usually 0.01 mm larger than the quoted number. For example, if the grille pitch is 0.25 mm, then the dot pitch (H) will be 0.26 mm. Variable Dot Pitch - Another complication related to dot pitch is that some monitors can have more than one legitimate vertical and horizontal dot pitch. You see, on flat screen monitors (more on these later,) the dot pitch is usually sharpest at the centre of the image and then a little lower around the edges. This is completely normal and is due to the extreme physics of having a scanning electron beam project a flat image over a surface with a variable distance from the source. I'll explain this in more detail for you later on, but I'll tell you this: If you see something like "0.25-0.26 variable grille pitch," it means that the grille pitch is sharpest in the centre and a little fuzzier outside. Subsequently the dot pitch will be 0.26-0.27 mm variable (again sharper in the middle, fuzzier on the outside.) If the manufacturer wanted to quote just one number for this case, they would probably tell you that it's a 0.26 mm (horizontal) dot pitch. Using this information on dot pitch, you should be able to decode the information given by the manufacturers and be able to find a common ground for its comparison. If one monitor is significantly worse than the others you're considering, then it's probably out of the running and your choice will be easier. Does "Flat Screen Technology" Really Do Anything? Yes, in fact it does! It's not a gimmick. Don't confuse flat screen technology with those really thin LCD Flat-Panel monitors. They're different things. Flat screen monitors are CRT (big, deep monitors) that have a completely flat viewing surface. If you look at a standard monitor, the screen looks like a bug's eye. It's curved like the side of a beach ball. If you normally use a standard curved monitor, your brain makes adjustments to make the image look flat, but in fact the geometry is distorted and you're not getting a geometrically correct picture. Also, the curved screen will reflect a lot of light into your eyes and make it hard to see the image on the screen. The thing about curved monitors is that they're easy to build. The electron gun has to hurl electrons a constant distance no matter where it's aiming at the screen. This means the electrons will always hit the screen at a 90 degree angle to it and the phosphor will shine light in the same direction. This makes the physics easy to handle and the monitor easy to manufacture. On the other hand, with flat screen monitors the electron will hit at a non-ninety degree angle when it lights up the phosphor. This means the beam of light will not go through the glass and into your eyes in a straight line because it's refracted. If you've studied introductory physics, you'll know that this is a case of Snell's Law. The vacuum of the cathode ray tube and glass of the viewing surface are of different densities and the light will bend to move through them when it enters at an angle. This results in a distorted (curved looking) image. To compensate, manufacturers usually curve the inside of the screen, but they try hard to not let you know because you might think that it's not "true" flat screen. Ultimately, the internal curvature allows for a flatter image because it corrects for some of the refraction. Although you might think it's a bad thing, internal curvature benefits the image flatness. The flat screen has another side effect too - the vertical edges are slightly darker than the middle and there's nothing you can do about it. Even in the very high end 19" flat screen monitors like the Sony Multiscan G400, the effect is present but hard to see because Sony does try to correct for it. The main benefits of flat screen technology are superior geometry and less glare. With flat screen monitors, you finally see the picture as it was meant to be seen. It's truly luxurious and completely worth the money. Second, the glare issue is also a great reason to buy a flat screen monitor. With curved monitors, you'll see reflections from all over the room on the screen. There's almost always some angle on the monitor that will create a bothersome reflection. But with flat screen monitors, they are usually coated with an anti-reflective coating, and since they're flat, a light will have to be right behind you to create glare. This is another reason why flat screen displays are wonderful. You might think that these points make flat screen monitors not worth your money, but in fact the problems mentioned are minor in comparison to the benefits. A flat screen monitor is incredibly nice, and after working on one for a while, you'll laugh when you see your friends' bulging bug-eye monitors. The picture that they get will simply be inferior to your eyes. Now you know exactly why you should eliminate non-flat screen monitors from your monitor short-list. Shadow Masks, Invar Shadow Masks and Aperture Grilles These three items are listed in order of worst to best. A shadow mask is essentially a piece of alloy with precisely punched holes in it. The holes allow the electron beam to accurately hit the phosphors and have its misfires blocked by the alloy. It makes the image less chaotic. The thing is, the shadow mask heats up and expands as it does its job. It then cools and contracts again when you turn the monitor off. The constant contraction and expansion of the alloy will eventually cause warping to some degree, blurring the image on the monitor. Also, shadow masks prevent a large number of electrons from getting to the screen, darkening the image. These are the main two disadvantages of shadow masks, and the reason why Invar Shadow Masks came into existence. Invar is an alloy that is resistant to the expansion/contraction effect, and resists the warping and distortion associated with standard shadow masks. Monitors on your list with invar shadow masks should get extra points over those with standard shadow masks. Invar masks are probably the reason why Aperture Grilles came into existence. Since the invar masks still block off a significant portion of the electrons, they darken the image more than what would be ideal. Aperture grilles, however, do not. They consist of vertical wires in a fine grille that still block out errant electrons but allow more light to get through. This creates a brighter, more detailed image. Aperture grilles are better and more expensive than both kinds of shadow mask. The primary disadvantages of aperture grilles are the horizontal damper lines. They are faint horizontal wires (1-3 of them) that keep the vertical wires in place. You can usually see their shadows on a bright coloured background. To some people, they are a minimal to non-existent problem, but to others, the wires drive them mad. If you know that the wires really bother you, then you should get a monitor that does not use an aperture grille. Picture Tubes (CRTs) The CRT is the primary factor determining the image quality of a monitor. At the time of writing, the most common high-end cathode ray tubes used in monitors are Sony's FD Trinitron and Mitsubishi's Diamondtron NF tube. Each one is used in many brands of monitors and employs different methods of providing a flat, geometrically correct, bright and accurate image. Suffice it to say, the Sony tube is superior and will usually give you a better picture. The Mitsubishi tube is nothing to sneeze at and is also very good. It is simply not as bright and accurate as the Sony one. Monitors with the Sony tube should be given extra points. Note that both tubes use aperture grilles and will have damper line shadows. In Conclusion... These points should give you additional bases of comparison when determining which monitors to scratch off your short-list. If you do determine the monitor you want, go check it out in a store. Look at the image, tweak the settings, and make sure it is to your liking. If everything goes right and the monitor you get is not defective, then you should have a product that you will be proud to say was chosen by you.  |
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