Am 17.10.2017 um 13:23 schrieb Kenneth:
> Alain <kua### [at] videotronca> wrote:
>>
>> On a CTR monitor, each pixel is spread over several groups of phosphore
>> patches. Also, the edges of the pixels are somewhat fuzzy, making them
>> blend together, at least, a little.
> 
> There's one aspect of a CRT that I still don't quite understand: The electron
> gun(s)--their beams--can be *deflected* using buttons on the CRT... meaning, you
> can 'squash and stretch' the image, so that it completely fills the screen (or
> not!) But the acreen's aperture mask or wire mask (with its discrete holes for
> the phosphors)is a fixed thing. So, I'm wondering how the squashed-and-stretched
> electon beams still manage to correctly 'line up' with those phophors (and it
> seems that they do, or the color mix on the screen would be completely messed
> up-- which it isn't.) I had always assumed that the magnetic bending of the
> beams was done in a continuously smooth way; it *appears* to be smooth. But is
> the squashing-and-stretching actually done in discreet steps, so that the
> individual  electron beams always *see* their own proper phosphors?

The trick is that there's nothing special about the squashing and
stretching.

During normal operation, the electron beam traces a zig-zag pattern
across the screen (of which only the zig is visible, as the electron gun
is effectively turned off during the zag). This would be virtually
impossible to align with the aperture mask, so no such attempt is even made.

The squashing and stretching is just a linear scaling of the beam's
current deflection on its way across the screen, so no magic is
happening there to the beam.

This regular deflection is achieved by one set of deflection elements
(either charged plates or magnets).

The real magic is that the three electron guns in the CRT are carefully
arranged (and possibly equipped with additional tunable deflection
elements and associated electronics), such that each beam hits the
aperture mask at a specific well-defined angle. The mask is carefully
aligned with the phosphor dot matrix and has only one aperture per
phosphor dot triplet, with the angles of the beams chosen in such a
manner that each hits its corresponding dot from the triplet as
precisely as technically feasible.

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