On Tue, 25 Mar 2008 11:54:32 -0500, chrisv
<chrisv@nospam.invalid> wrote:
>Calab wrote:
>
>><void.no.spam.com@gmail.com> wrote in message
>>news:a5be52d6-87ee-4f90-a0dc-8f06257e53a9@8g2000hse.googlegroups.com...
>>> Someone just gave me a 19" CRT monitor, and I noticed a geometry
>>> problem with it. It seems that the top edge and bottom edge of the
>>> image are not parallel with the top and bottom of the monitor. The
>>> right side of the top edge and bottom edge of the image touch the top
>>> and bottom of the screen, but the left side of the top edge and bottom
>>> edge are a few millimeters from touching the top and bottom of the
>>> screen.
>>
>>CRT monitors are designed to have about a 1/4 inch of blank display all the
>>way around the picture.
>
>Since when? Ideally, the image shoud cover 100% of the usable area.
>(Of course, the tube itself is larger than that.)
>
>>Set it this way and you probably won't notice the misalignment.
>
>Not sure why not...
It depends on the cause, on a typical CRT the last few
percent of the usable area is geometrically distorted. Some
would rather have the entire display bigger by using this
area (including a monitor manufacturer selling by # of
inches who doesn't want to irk the customer by not using as
much of the space as possible) but some would rather leave a
small border to keep geometry correct.
Maybe a better question is why fool around with an old CRT
monitor with problems - probably why it was given away.
There might be an adjustment inside but without a service
manual all one can do is open it and see what they see, or
pay a tech to look at it but I hardly think it worthwhile
for an old 19" CRT.
>"chrisv" <chrisv@nospam.invalid> wrote in message
>news:rebiu3pcseavscittnkse33pnqs30trac4@4ax.com.. .
>
>>>CRT monitors are designed to have about a 1/4 inch of blank display all
>>>the
>>>way around the picture.
>>
>> Since when? Ideally, the image shoud cover 100% of the usable area.
>> (Of course, the tube itself is larger than that.)
>
>That all depends on what you define as the "usable area," and
>whether or not the opening in the monitor bezel encroaches on
>that area.
>
>In most CRT specs (the tube itself, not the monitor), there is a
>"recommended image area" which is smaller than the full extent
>of the phosphor screen. In part, this area is determined by what's
>going on re the curvature of the inside of the glass faceplate as you
>get to the edges of the tube (obviously, at some point that inner
>surface is no longer anything even remotely resembling "flat," and
>the geometry, etc., starts to go bad quicky in those regions. In
>part, the area is also determined by the performance of the yoke
>(at least a "typical" yoke as expected for that tube type, the focus
>electronics, etc., convergence, etc., also going away as you get
>close to the extreme edges. For monitor tubes, this results in
>the optimum image area being somewhat smaller than what you
>might expect from just looking at how big an area the phosphor
>covers.
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...
Of course, in modern CRT monitors (an oxymoron?) digital geometry
controls can go a long way toward correcting problems. I suppose that
the "pincushion" controls normally affect only the sides, since the
display is wider than it is tall, making doing the sides correctly
more difficult than top and bottom.
>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.
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.
>"chrisv" <chrisv@nospam.invalid> wrote in message
>news:rebiu3pcseavscittnkse33pnqs30trac4@4ax.com.. .
>
>>>CRT monitors are designed to have about a 1/4 inch of blank display all
>>>the
>>>way around the picture.
>>
>> Since when? Ideally, the image shoud cover 100% of the usable area.
>> (Of course, the tube itself is larger than that.)
>
>That all depends on what you define as the "usable area," and
>whether or not the opening in the monitor bezel encroaches on
>that area.
>
>In most CRT specs (the tube itself, not the monitor), there is a
>"recommended image area" which is smaller than the full extent
>of the phosphor screen. In part, this area is determined by what's
>going on re the curvature of the inside of the glass faceplate as you
>get to the edges of the tube (obviously, at some point that inner
>surface is no longer anything even remotely resembling "flat," and
>the geometry, etc., starts to go bad quicky in those regions. In
>part, the area is also determined by the performance of the yoke
>(at least a "typical" yoke as expected for that tube type, the focus
>electronics, etc., convergence, etc., also going away as you get
>close to the extreme edges. For monitor tubes, this results in
>the optimum image area being somewhat smaller than what you
>might expect from just looking at how big an area the phosphor
>covers.
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...
Of course, in modern CRT monitors (an oxymoron?) digital geometry
controls can go a long way toward correcting problems. I suppose that
the "pincushion" controls normally affect only the sides, since the
display is wider than it is tall, making doing the sides correctly
more difficult than top and bottom.
>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.
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.
"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.
"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.
>"chrisv" <chrisv@nospam.invalid> wrote:
>>
>> 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,
Well, when I wrote "why have phosphor there", I meant "why have
phosphor and shadow mask" there, or, phrased another way, why have
usable display area there (if one really ought not use it).
I suppose it's sensible to allow the choice of a maxxed-out display
size, or to sacrifice some size for accuracy... Although not many
would be (or should be) so fussy, IMO...
>"chrisv" <chrisv@nospam.invalid> wrote:
>>
>> 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,
Well, when I wrote "why have phosphor there", I meant "why have
phosphor and shadow mask" there, or, phrased another way, why have
usable display area there (if one really ought not use it).
I suppose it's sensible to allow the choice of a maxxed-out display
size, or to sacrifice some size for accuracy... Although not many
would be (or should be) so fussy, IMO...
"chrisv" <chrisv@nospam.invalid> wrote in message
news:gcdlu3pbfkjvcvc5f5jlj48kcp6f4j0u8d@4ax.com...
>>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,
>
> Well, when I wrote "why have phosphor there", I meant "why have
> phosphor and shadow mask" there, or, phrased another way, why have
> usable display area there (if one really ought not use it).
Again, because of the way the phosphor screen is produced.
and other needs (re the aluminization step I mentioned) to make
the CRT producible. "You can't easily NOT have phosphor
there" is the short form answer, and you don't WANT that
area to be completely open, for other reasons. But again,
just because it's there doesn't mean it's a good idea, from
the standpoint of focus, purity, convergence, and geometry
concerns, to actually try to use it. TV is another story, and
clearly much less concerned with this issues vs. the typical
monitor application.
"chrisv" <chrisv@nospam.invalid> wrote in message
news:gcdlu3pbfkjvcvc5f5jlj48kcp6f4j0u8d@4ax.com...
>>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,
>
> Well, when I wrote "why have phosphor there", I meant "why have
> phosphor and shadow mask" there, or, phrased another way, why have
> usable display area there (if one really ought not use it).
Again, because of the way the phosphor screen is produced.
and other needs (re the aluminization step I mentioned) to make
the CRT producible. "You can't easily NOT have phosphor
there" is the short form answer, and you don't WANT that
area to be completely open, for other reasons. But again,
just because it's there doesn't mean it's a good idea, from
the standpoint of focus, purity, convergence, and geometry
concerns, to actually try to use it. TV is another story, and
clearly much less concerned with this issues vs. the typical
monitor application.
>"chrisv" wrote:
>>
>> Well, when I wrote "why have phosphor there", I meant "why have
>> phosphor and shadow mask" there, or, phrased another way, why have
>> usable display area there (if one really ought not use it).
>
>Again, because of the way the phosphor screen is produced.
>and other needs (re the aluminization step I mentioned) to make
>the CRT producible. "You can't easily NOT have phosphor
>there" is the short form answer,
But you CAN easily not have shadow-mask there.
>and you don't WANT that
>area to be completely open, for other reasons.
There are other alternatives between shadow-mask and completely open,
right?
>But again,
>just because it's there doesn't mean it's a good idea, from
>the standpoint of focus, purity, convergence, and geometry
>concerns, to actually try to use it. TV is another story, and
>clearly much less concerned with this issues vs. the typical
>monitor application.
Re: CRT monitor geometry problem 
Linear Mode
