The maximum resolution of a monitor is dependent on more than just its highest scanning frequencies. Another factor is dot pitch, the physical distance between adjacent phosphor dots of the same colour on the inner surface of the CRT. Typically, this is between 0.22mm and 0.3mm. The smaller the number, the finer and better resolved the detail. However, trying to supply too many pixels to a monitor without a sufficient dot pitch to cope causes very fine details, such as the writing beneath icons, to appear blurred.

There’s more than one way to group three blobs of coloured phosphor – indeed, there’s no reason why they should even be circular blobs. A number of different schemes are currently in use, and care needs to be taken in comparing the dot pitch specification of the different types. With standard dot masks, the dot pitch is the centre-to-centre distance between two nearest-neighbour phosphor dots of the same colour, which is measured along a diagonal. The horizontal distance between the dots is 0.866 times the dot pitch. For masks which use stripes rather than dots, the pitch equals the horizontal distance between two same coloured strips. This means that the dot pitch on a standard shadow mask CRT should be multiplied by 0.866 before it is compared with the dot pitch of these other types of monitor.

Some monitor manufacturers publish a mask pitch instead of a dot pitch. However, since the mask is about 1/2in behind the phosphor surface of the screen, a 0.21mm mask pitch might actually translate into a 0.22mm phosphor dot pitch by the time the beam strikes the screen. Also, because CRT tubes are not completely flat, the electron beam tends to spread out into an oval shape as it reaches the edges of the tube. This has led to some manufacturers specifying two dot pitch measurements, one for the centre of the screen and one for the its outermost edges.

Overall, the difficulty in directly comparing the dot pitch values of different displays means thatother factors – such as convergence, video bandwidth and focus – are often a better basis for comparing monitors than dot pitch.

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