a picture is set by the brightness of the unexcited phosphor, which is governed by the degree with
which ambient light is reflected. Contrast is therefore reduced in conditions of high ambient light
levels. Black Matrix tubes reflect less ambient light so exhibit higher contrast than other tubes.
Convergence error
Bean misalignment causing one or more of the three beams passing through the wrong aperture in
the shadow mask and striking a phosphor dot in the wrong triad.
Convergence error is expressed in mm often at three well-defined points on the screen, designated
A, B and C (see figure ). Also known as misconvergence.
Points where convergence error is specified
.
Convergence-error correction
A method of correcting for convergence error to insure that all three beams land simultaneously in
the same triad. This is usually accomplished by means of special convergence-error correction coils
in the deflection yoke.
CRT
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