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A special grating is described for use with a CRT display such that the qualities of the CRT focus, line spacing, line width, etc., may be readily determined by visual means.
English (United States)
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CRT Line Width Magnifier
A special grating is described for use with a CRT display such that the
qualities of the CRT focus, line spacing, line width, etc., may be readily
determined by visual means.
The grating, which consists of a series of straight parallel clear and opaque
bands, is supported as a photographic, printed or similar record on either a film,
plastic or glass substrate. The unit is intended to be used either hand-held or
temporarily fixed to the front of the display screen by, for example, adhesive
The period of the grating is made to be slightly different to that of the CRT
raster, and the clear bands made much narrower than the opaque bands and,
more particularly, narrower than the CRT line width. The light transmitted by the
grating from a CRT screen will be the product of the two waveforms. The beat,
or difference frequency, predominates and when the CRT pattern is a full close
packed line block, the resultant effect is that the line width appears magnified by
a reciprocal of the relative difference frequency. (A 10% frequency difference
gives a magnification of 100X.)
When used with a CRT unit having a thick protective glass front, resolution is
improved if the grid is mounted on a fiber-optic faceplate. In this case the fiber-
optic plate ensures that only light direct from the required CRT line reaches the
The figure shows the distribution of light from a CRT screen. ]The pattern will
appear as a virtually continuous waveform...