A THG Primer: CRT Guide

Shopping Around

In an ideal world, you could go into a store and see dozens of monitors, and they'd already be connected to PCs with the same graphics board that you will be using at home, and under the same lighting conditions. You would install monitor calibration software (such as that from DisplayMate Technologies) on each of the systems, spend a few hours calibrating each monitor and run through the diagnostics. When you finally select the best monitor for your needs, the friendly employee would disconnect it, box it back up in the original carton, and you'd be able to take that particular monitor home with you. Unfortunately, it is not an ideal world, and there aren't many stores that would allow you to do that. Even if you could test a few monitors on the show floor, they would probably give you one from their storeroom of- the same make and model, but not the exact monitor you had seen on the floor.

That brings up an important point - no two monitors are exactly alike. I'm not just talking about differences between brands, or even model numbers. Even units of the same model from the same manufacturer can perform quite differently. Sometimes you get lucky - sometimes not.

If you're in the market for a new monitor, there are a few things to consider before you start. Perhaps the most important factor is matching the monitor to your normal operating screen resolution. In the old days, monitors were fixed at certain frequencies and resolutions (LCD panels still are), but these days most CRT monitors will run at a variety of frequencies and resolutions. But even though a multi-scan monitor will function at different frequencies and resolutions, some CRT monitors function better at certain resolutions and strain in order to run at others, which shortens their life. A more expensive monitor designed to run best at 1600 x 1200 won't look quite as good if you run it at 1024 x 768. Unfortunately, many monitor manufacturers tend to highlight their maximums and downplay their optimum settings. In general, most monitors are designed to operate at peak efficiency at about 85Hz. If a monitor data sheet gives you a wide range of possible resolutions at different frequencies, look at the 85Hz values to get an idea of what its optimal settings should be.

  • 85KHz Class = 1024 x 768 @ 85Hz
  • 95KHz Class = 1280 x 1024 @ 85Hz
  • 107KHz Class = 1600 x 1200 @ 85Hz
  • 115KHz Class = 1600 x 1200 @ 92Hz
  • 125KHz Class = 1856 x 1392 @ 85Hz

If you normally run at 1600 x 1200 resolutions, then you should look for a monitor in the 107 or 115 kHz class. Using a lower class monitor will require overdriving it, which will not only give a generally lower-quality image; but may also reduce the life of the monitor. On the other hand, if you normally run at 1024 x 768 or lower, then buying a higher-class monitor and running it at lower resolutions can produce moiré patterns and give you less than optimal performance (not to mention the fact that you are also wasting money).

If you want to get the best picture from an existing monitor, you can work the numbers backwards. Take the horizontal size of the display area and divide by the dot pitch; then, set the resolution to the nearest setting just below that. For example, a 19" monitor typically has a horizontal viewable area of 360mm. Let's assume it has a 0.22mm horizontal dot pitch. 360 / 0.22 = 1636 dots across the screen. So, the best setting is probably 1600 x 1200 at 85Hz. A monitor with the same viewable area and a 0.24mm horizontal dot / aperture pitch has 1500 dots. So, the best setting would probably be 1280 x 1024.

Vertical resolution isn't as problematic. A typical 19" monitor has a vertical viewable area of 270mm. Because aperture grill monitors use vertical stripes, they have a 0.00mm vertical aperture pitch, so vertical resolution capability is virtually unlimited. As with every technology, there's a trade-off - here, the downside is that more beam current hitting the phosphors makes them more susceptible to screen burn. Use a screen saver!

Most shadow mask monitors have a 0.14mm vertical dot pitch. 270 / 0.14 = 1928 lines - far more than any current video card can produce at any decent refresh rate.

The pixel rate and the horizontal scan frequency determine the resolution and refresh rate of the monitor.