"chrisv" <chrisv@nospam.invalid> wrote in message
news:vkjku3dvhej854s43ft1r3t5diac6p5iai@4ax.com...

> Hmm... Can't say that I've ever heard of that. Doesn't make a lot of
> sense, really - if the performance "sucks" beyond a certain
> scan-angle, why have phosphor there? I suppose choice is nice...

Because of the way the phosphor is deposited. It's
basically poured into the faceplate glass as a slurry,
over a photoresist mask which is produced by using the
shadow mask or aperture grille as an exposure mask.
This results in phosphor being deposited well up the sides
of the glass, which is a good thing because then you also
need to aluminize the back of the phosphor (done later on
in a vacuum-dep process, after the funnel has been mated
to the faceplate) to provide the actual "2nd anode" of
the tube.


>
>>TVs are a bit different in that they are commonly "overscanned" -
>>i.e.., the scanned image actually extents beyond the edges of the
>>phosphor screen by about 5-10%. This basically hides edge
>>geometry and other problem by placing them where the viewer
>>can't possibly see them.
>
> The distortions are still present near the edge of the phosphor screen
> where they can be seen, of course (although certainly far less obvious
> than they would be if you could see the "edge" of the scan.

Yes, but often hidden by the bezel of the TV.

> Personally, I loath the concept of overscanning in televisions. I
> know why it's done, but it throws-away information in a situation
> (NTSC) that has none to spare. My last CRT TV had some service-menu
> options to reduce/eliminate overscan, which I did, despite noticable
> distortion of the image in the last half-inch on one side.

The practice should, of course, become less common with the move
to digital television and flat-panel display technologies, but unfortunately
it is still with us even with many HDTV transmissions.

Bob M.