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Arfa Daily

"Smarty" wrote in message
...
On 6/3/2013 9:54 PM, wrote:
There is purity, which is making sure the
3 beams hit their respective phosphors.

Let us assume that for some reason, all three electron guns come in at
an incorrect angle thru the shadow mask or grid or screen. The blue
electron gun hits 50% on the blue phosphor and 25% on the red and 25%
on the green phosphor. The red gun hits 50% on the red phosphor and
25% on the blue and 25% on the green phosphor. The green gun hits 50%
on the green phosphor and 25% on the red and blue phosphors. All
three phosphors are illuminated at 100%, so only differing electron
beam strengths due to compensating for differing phosphor efficiencies
will be noticeable in any color shading of white and gray areas of the
picture.
Your chosen example that the 3 guns are mis-registered uniformly, and that
the phosphors are all illuminated to 100% is not realistic. The
differences in phosphor efficiencies and the necessary beam currents to
achieve comparable light outputs are, as you acknowledged, quite
different. More important is the fact that mis-registered beams are not,
in general, spilling their mis-directed energy to reach 100% phosphor
saturation during a black and white program (versus the full white example
you have chosen). In general they will be generating beam currents on the
average well below peak white and perhaps closer to black. The
instantaneous beam current for, let's say, the least efficient phosphor's
gun, will be mistakenly exciting the most efficient neighboring phosphors
at the same time as the exact opposite is occurring for nearby areas of
the screen owing to the fact that the most efficient gun is simultaneously
exciting the wrong phosphor area with too little energy. If the proposed
mechanism / concept made sense theoretically, then a black and white
picture should not show colored regions due to magnetization at all.

The ability to discern color differences has as much to do with human
vision as it does with the pure physical radiation of visible light from
the phosphor surfaces, and my partial explanation is that humans see color
variations which are much more subtle at some frequencies compared to
others. White and shades of gray reveal less whereas some color fields
reveal more.

For purposes of our discussion, the esential ingredient of impurity of
color is the non-homogeniety of the electromagnetic field due to
uncontrolled magnetic influences arising from nearby magnetized areas
including the shadow mask. To the extent that we are talking about pretty
drastic purity issues causing large blotches of color, some areas of the
CRT will have gross errors due to landings which are at the extremes of
the convergence system (and thus more likely to be visible) or beyond the
intended raster limits. Recall that the purity control of the CRT and
degausser is intended to deal with the extremely small and subtle effects
of the Earth's magnetic field, whereas abrupt failure of the degausser is
likely to impart a much bigger residual effect unless corrected. Also, the
magnetic distortion is, unlike the Earth's field, very localized and
highly non-linear across the CRT surface, making the assumption that
spoiling of the beams occurs in any uniform way highly unlikely.

All of which is jolly interesting. Pity it doesn't match the actual facts,
as have been repeatedly put to you by a number of people very well qualified
to comment, by virtue of the fact that collectively, they spent a very long
time time working on this stuff at nuts and bolts level, and have probably
seen every possibility of purity error on every type of CRT and under every
set of circumstances possible ...

Arfa