Yikes, Holy Focus Guy Kuo - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #1 of 163 Old 12-07-2001, 02:10 PM - Thread Starter
AVS Special Member
 
stefuel's Avatar
 
Join Date: Apr 2001
Location: Marshfield, MA, USA
Posts: 5,880
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 13
After spending 8 hrs yesterday experimenting with all the information and advice given to all of us from the experts here on the forum, was able to get my ECP looking the best I've ever seen it. In fact, that after following Mike Newmans instructions for setting up an ECP, I can do a hard reset and have an image that's almost watchable (about 75% converged). So when I was done last night I thought, Thats it, thats all she's got. Wrong. I decided to try Guy Kuo's focus technique. Very time consuming, frustrating and worth every minute of it. About 1 1/2 hrs a piece for this partly because the tubes need to be cleaned off first or you may confuse dust on the face for phosphor grain. What this technique does is takes the guess work out and leave you with a stunning 3-D picture that you can't help but notice. The first 15 seconds of Cats and Dogs where the camera pans down through the trees made me feel as though I was floating down there myself.

Thank's to All

Chip S.

Current owner of the last/best AmPro on the planet. The mighty 4600HD, and it's still running...better than Barco's, especially southern ones.
stefuel is offline  
Sponsored Links
Advertisement
 
post #2 of 163 Old 12-07-2001, 02:58 PM
AVS Special Member
 
KennyG's Avatar
 
Join Date: Jul 2000
Location: within the unlimited boundries of my imagination
Posts: 3,994
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Where did you find Guy's focus instructions...I just tried to do a search but am having a problem loading anything but the first page of his posts.
KennyG is offline  
post #3 of 163 Old 12-07-2001, 03:20 PM
Advanced Member
 
Kevin Coleman's Avatar
 
Join Date: Mar 2000
Location: Wichita KS USA
Posts: 648
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
no kidding spill the beans

Stop DFAST.
Boycott JVC!
Kevin Coleman is offline  
post #4 of 163 Old 12-07-2001, 06:38 PM
Senior Member
 
shanemac's Avatar
 
Join Date: Aug 2001
Location: Victoria, BC
Posts: 363
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I am also looking for top notch focus instruction... but when I do a search on the forum... all the links come up like this one

http://www.avsforum.com/avs-vb/showt...+a+Runco%2FNEC

totally blank

Shane
shanemac is offline  
post #5 of 163 Old 12-07-2001, 07:01 PM
AVS Special Member
 
Steve Smith's Avatar
 
Join Date: Feb 1999
Location: Enumclaw, WA
Posts: 1,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 10
I believe this is what you're looking for.

Steve
Steve Smith is online now  
post #6 of 163 Old 12-08-2001, 06:07 AM
AVS Special Member
 
jcmccorm's Avatar
 
Join Date: Mar 2001
Location: Madison, AL, USA
Posts: 3,370
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 13
Ok, I read the re-post of Guy's post (and I want *my* ECP to look it's best). My only question is that at one point, Guy says to show the "EM pattern". What's that?

Cary
jcmccorm is offline  
post #7 of 163 Old 12-08-2001, 06:14 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The "EM" pattern is Sony's internal focus pattern which is looks like the letters E & M.

I'm going to combine a few of my focus and astig posts into a single post here.

Guy Kuo
Guy Kuo is offline  
post #8 of 163 Old 12-08-2001, 09:02 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
CRT PROJECTOR FOCUS & MECHANICAL AIM BASICS (updated 12/25/2004)

Guy Kuo

Ovation Multimedia, Inc. - Home of

Avia PRO
AVIA Guide to Home Theater DVD
Sound & Vision's Home Theater Tune-up DVD


Focusing and aiming a CRT projector is a daunting task. It involves two projection systems which operate in series - optical and beam focus. Problems in one system make it difficult to see problems in the other. As a result, first time owners are sometimes at a loss as to which system is the problem. Add to that the need to astigmate the electron beam and adjust lens flapping (Scheimpflug) and the novice CRT setup can fall far short of the projector's optimum.

Read through this document in its entirety before proceeding. At first, it will seem as though some steps are discussed in jumbled order. I have attempted to present this in sequence but one must perform tasks iteratively to achieve the final result. One revisits earlier steps because later steps make earlier ones easier to do more accurately.

--------------------------

Equipment Recommended:

An external test pattern DVD such as AVIA or S&V HTT or a test signal generator provide the signals needed for alignment.

A good pair of binoculars which can focus at SHORT distances is very helpful for critically observing the effect of adjustments.

One roll of 3M brand blue easy release masking tape for marking the center of screen surface and edges. Do NOT substitute another brand of tape.

Tape measure to find center of each screen edge

Laser Pointer or CLEAN straight edge for finding screen center

---------------------------


RASTER, IMAGE AREA AND INTERNAL TEST PATTERN CENTERING ON TUBE FACES

Centering of the image on the tube phosphor surface is done by centering the raster on tube phosphor and then centering of the actual image within the raster. You should begin by hooking up and displaying a video source.

Raster - The area of the tube phosphor that is painted by the electron beam.

Normally, only part of the raster is actually used to produce the image. The raster can be seen by peering through the lens after turning down contrast nearly all the way and then raising brightness to make the normally black raster light up. This makes the entire raster light up dimly. It may be necessary to open the left, right, top, and bottom blanking controls to allow visualization of the entire raster. Size of the raster is adjusted using vertical and horizontal size (aka amplitude) controls. The rasters are best kept small enough to ensure active video image is never extended beyond or near the phosphor edges. Keeping at least 7 to 10 mm of unused phosphor on all edges helps prevent the catastrophic tube failure that will occur if active image is projected beyond or too close to the phosphor edges. Since the raster is usually larger than the actual image area and it is actually the energy of the image area that can cause damage, some installers will allow the raster to extend beyond the edges while still maintaining image area within the safe portion of the phosphor.

When viewed on screen, the leftmost portion of the raster is drawn first after the electron beam completes horizontal retrace. Looking into the projection lens the orientation is backwards. During the first portion of the horizontal movement the beam has not settled completely and one may see some waviness in the image if the extreme left edge of the raster is used. Some installers will intentionally displace the raster slightly leftward so the active image is displayed on the later, more stable portion of the raster.

Centering the raster is performed by use of centering magnets on the CRT necks just behind the deflection yokes. The centering magnets are a pair of rings with small tab handles. By rotating the rings relative to each other and also around the neck of the tube one can shift the raster about the phosphor surface. Most projectors also have electronic static position controls for fine adjustment of the raster centering. It is best to use minimal electronic correction to reduce strain on the convergence circuitry. One can do so by centering the electronic controls prior to centering the raster with the centering magnets. On some projectors (such as NEC XG's), there are no centering magnets and raster centering is carried out purely with electronic controls for raster centering hidden in a service menu. Even on such machines it is reasonable to first center the user centering controls prior to setting the service menu raster centering controls.


Image Area - The portion of the raster which is actually used to display the video image

Within the raster, the active video image is displayed. The projector often has "position" or "image shift" controls which allow movement of the image within the raster. The name of this control varies from brand to brand. You can verify you have the correct control by making the raster visible and seeing if the image is moving about within the raster but the raster is not moving as you use the control. If raster moves as well as the picture, you are adjusting the raster position and not the image position within the raster.

Ideally, the image area is centered both vertically and horizontally on the phosphor surface. You can achieve this by first neutralizing the linearity controls and then centering the raster relative to the phosphor edges. Then center the image area within the raster edges. Once both are done, display a white field pattern from a calibration disc (AVIA, S&V Home Theater Tune-Up) and verify that the active is centered in the phosphor. We'll cover this in greater detail later.

BTW, Don't use an internal test pattern for checking centering as they are often not themselves centered relative to external signals unless you have also taken the steps described next in this note.

Internal Test Pattern Centering

Built in test pattern generators do not necessarily coincide with actual video signals in timing. They tend to be off center and not exactly scan locked to match a real signal. This means that making an internal test pattern look correct does not necessarily optimize the machine for a real signal. However, internal test patterns are handy and some machines like NEC's actually require you to set their timing relative to the video signal and convergence systems to prior to other geometry and convergence adjustments. If you have a machine which allows adjustment of internal test pattern timing, it is possible to center the internal test patterns to coincide with the center of actual video signals. This is much easier to do if mechanical gun aim has already been accomplished. In the next section, mechanical gun aim will be covered so skip forward and do that. Then set internal test pattern centering (phase) as described below.

For example, the phase control of NEC projectors MUST be set before geometry and convergence adjustments when creating a new input memory. The phase control changes the timing of the internal test pattern generator and also timing of the convergence system relative to the video signal. Since you have already centered the gun mechanical aim and centered the image on the screen and phosphor surfaces, adjusting phase to make the internal generator centered on screen also centers it with the video image center. Adjust phase to make the center vertical line of the internal generator centered left/right on screen. Then adjust phase to make the deflection blip centered around the center vertical line. The blip shows the centering of the convergence system. If it makes it easier for you, display the internal center cross pattern rather than the crosshatch while adjusting phase. Ignore the odd shape of the lines, just concentrate on the position of the middle of the center vertical line and the blip.

Since there is no control to shift the internal test pattern vertically, the only way to achieve vertical coincidence of the image and internal pattern centers is the image position control. Once that is done, you may need to readjust projector tilt to get things centered on screen. Going through all gains you the option of using either internal or external test patterns with good accuracy.

One should strive to keep the image centered within the phosphor surface and leave at least 7 to 10 mm of unused phosphor all around the active image. Mechanical aim of the guns is easier to do when the image and rasters are vertically and horizontally centered on the tube faces. Further fine tuning of raster and image centering can be performed as well as centering of the internal test pattern generator once gun aim is accomplished.

---------------------------

MECHANICAL GUN AIM

If your projector has lens tilt rings, set them to factory spec for your projection distance before doing any aiming.

You must first mechanically aim the guns properly. Most CRT projectors have red and blue lens/CRT assemblies (aka gun assembly) capable of swinging left/right. Up/down mechanical aim is accomplished by altering projector tilt. These movements mechanically aim the center of all three guns so they converge at screen center. Typically four bolts accessible at the bottom edge of the gun assembly secure the gun. These are loosened to free the lens and gun assembly and allow left/right swing. Do NOT REMOVE all four screws. Merely loosen them. Check in your installation manual to verify which screws need to be loosened. Some projectors only have a few fixed swing angles which are secured by placing a locking screw through specific drill holes. Others allow infinitely variable convergence angle and are secured by placing the locking screw through an arc shaped slot instead of a hole. The green gun usually isn't adjustable left/right so getting the projector centered and square to the screen during mounting is vital.

The guns sometimes stick in their prior position even when the screws are loosened. Controlled pressure can free a gun, but never force the guns because a sudden give way motion could snap a tube neck. One method of producing controlled pressure is to place some fingers between the lenses and gradually form a fist. This allows considerable pressure to be exerted without risk of sudden excessive motion. Once freed, just point each gun exactly and lock them in position. How that is accomplished comes next.

Marking Screen Center

Mark the your projection screen's exact midpoint of each edge (top, bottom, left, right) with a triangle of 3M blue easy release tape. Then mark the exact center with a LIGHTLY applied triangle of the same tape. This tape, if left for less a few hours, should not mar a screen. At least it never has in my hands. I cannot say the same for other brands so I suggest no substitutes. Finding screen center can be accurately done using a laser pointer placed at one screen edge midpoint marker and bouncing the beam off the screen surface to make a spot at the opposing midpoint marker. If a laser is not available, a tape measure can suffice so long as care is take to avoid marking the screen with tape measure.

Aiming the Guns

The traditional method of setting mechanical aim is to display a center cross, center the cross in each phosphor and then swing the guns and tilt the projector to place the projected red, green, and blue crosses all at screen center. The problem with the traditional technique is the difficulty in judging when the center cross pattern is accurately centered on the phosphor. I prefer an alternative technique which is easier to visually judge ? centering using edges. Basically, this takes advantage of how easy it is to accurately judge evenness of the gap between test pattern edges and the phosphor edges.

Turn down contrast and display a white field pattern and shift the raster to make the edges of the pattern equidistant relative to the phosphor edges. Look into the lenses while doing this, not at the screen. You will need to do this for each gun. The pattern will be widest at the CRT bottom assuming ceiling mount. Adjust size and position left/right to assure the pattern is well clear of the phosphor edges and equally spaced from the edges at its greatest left and right extents. Adjust the pattern up/down to achieve even spacing for the top and bottom edges as well. Once that is done, the pattern is precisely centered left/right and top/bottom on the phosphor surface. All you need to then is mechanically aim the guns to project that centered pattern so its edges are centered relative to the projection screen.

Look at the top of the projection screen and examine the left/right relationship of the projected pattern edges and the screen edges. Swing the gun left/right to equalize the edge relationships. Don't worry if the red and blue guns are not yet the same width. Just make sure the edges are balanced left/right for each gun. Lock the CRT's into position. They are now precisely mechanically aimed left/right.

Next, pay attention to how the projected white field pattern is positioned vertically using just the green gun. You should have previously set the pattern so is centered up/down on the phosphor. Adjust projector tilt up/down to make the projected green white field edges equally balanced relative to top and bottom screen edges. Now for more explanation.

If you happen to know your center cross pattern is already precisely centered you can just use the center cross to aim the tubes. Unfortunately, the most accurate way I know of doing that is to pull the lenses off, center the cross on the phosphor while measuring with a ruler, then remounting the lenses. The white field pattern edge comparison method described above allows easy, accurate physical aim and centering on the phosphors without pulling the lenses. This also gives a subtle plus for the red and blue guns as I'll explain later.

I know this method seems backwards, but balancing the edges of a white field pattern against the edges of the phosphor and then the projected edges relative to the screen edges achieves precise mechanical aim in an easy manner. The advantage to this method is basically the difference between having someone mark the middle of a piece of paper without aid of a ruler vs aligning a slightly smaller piece of paper so it is uniformly spaced inside the larger piece of paper. The latter is easier to do accurately.

Consider the off center red and blue guns. If you aim the actual center of the phosphor of those tubes to project at the center of the screen, you'll note that the phosphor usage distribution is unequal left/right due to the throw angle. Graph it out and you will see that the farther half of the screen gets illuminated with a smaller area of phosphor. Ever notice how the side of the screen opposite the side of the gun is less well focused? This is part of the reason.

Centering a field pattern relative to the phosphor and then using those lit up edges to guide lens aim will actually place the red and blue guns so they are mechanically slightly off true center. The left lens ends up pointed slightly left of center and the right lens ends up slightly right of center. At first blush, this seems wrong, but this can actually be advantageous because it makes the raster usage, resolution, and illumination more uniform across the screen. Less horizontal linearity compensation and lens flapping are needed.

Now if you are a traditionalist and want the center of the phosphor actually aimed at the center of the screen, you can pull the lenses off, set the center cross with great precision and then use the projected center cross position to guide mechanical aim. This is the usual way things are done, but I present an alternative approach with some advantages.

You have now precisely aimed the gun assemblies. From now on, anything projected that appears centered on the screen is also appropriately centered on the phosphor.

----------------

Note: Mechanical Aim is Not Scheimpflug (Lens Flapping)

Novices confuse the two, but mechanical aim is not the same as lens flapping (aka Scheimpflug). Mechanical aim of the CRT/lens assembly is akin to taking a telescope and physically pointing it at something. Lens flapping adjusts the mounting angle of the end lens without changing the direction the telescope is pointed. Lens flapping doesn't change the direction of aim (well just a little), but compensates for the planes of the screen and phosphor being non-parallel. If the lens were kept parallel to the phosphor surface, it would be impossible to focus throughout the screen at the same time. The flapping places the lens into a plane intermediate between those of the screen and phosphor and that makes global focus possible.



-------------

ROUGH OPTICAL FOCUS

Now that mechanical aim of the guns has been done, it is time to do an initial, rough optical focus.

Display a crosshatch pattern. Adjust optical focus using the two knobs. The front most knob on the lens controls edge optical focus. The rear most knob adjusts center optical focus. Dial in center focus first. Then adjust the outer (front knob) focus to while watching the corner lines of the crosshatch flare inward and outward. Try to minimize flaring using the outer focus knob. Go back and forth between the two optical focus knobs to get both center in focus and outer edge minimally flared. Use of binoculars aids this process tremendously.

--------------

ROUGH SCHEIMPFLUG (LENS FLAPPING)

Once rough optical focus is completed, you can perform lens flapping. The following is primarily for projectors which have continuously variable lens flapping. For projectors with lens flapping rings, simply set the lens rings per the installation manual specified settings for your projection distance.

Display a focus pattern. Look ONLY at the center of the top edge. Adjust center optical focus to make that edge sharpest. Note the position of the focus knob. Pay attention to the center of the bottom edge. Adjust lens center focus to make the bottom edge sharpest. Is the lens center focus control in the same position as when the top was sharpest? If so, vertical flapping is correct. If not, adjust vertical flapping using a wrench. Note the wrench position when the bottom edge is focused vs top edge. Set the vertical flapping to put the wrench in exactly halfway between the two positions. Horizontal flapping is performed in an analogous fashion paying attention to only the left and right edges.

Now go back and refine center and edge lens focus. Once that is done you should have the lenses in fair optical focus and flapping. Advanced owners may consider the 3 x 5 card technique fine focusing technique presented later in this document for even better optical focus and Scheimpflug.

--------------------

Phosphor Grain Optical Focus Technique for when the Electron Beam Has not been Focused Yet

Most people have difficulty deciding whether optical, beam or both kinds of focus problems are present, particularly if they have not already achieved good beam focus. Here is a trick for setting good optical focus without being confused by beam focus. You must have a good pair of binoculars which focus at a short distance to use this technique.

The phosphor surface of a CRT has an inherent grain pattern. Because this grain is visible and is exactly at the plane of light generation, one can use the grain to set optical focus independent of beam focus. A small piece of 3M easy release blue masking tape aids in keeping your eyes correctly focused on screen. Display a bright window pattern and intentionally defocus the electron beam to make the scan lines disappear. Adjust center optical focus while viewing the screen through binoculars. When optical focus is correct, the inherent grain pattern of the phosphor surface suddenly snaps into view. This is nearly impossible to see with naked eye, but binoculars make it readily evident.


------------------


ELECTRON BEAM FOCUS

The electron beam focus system in a projector can be a simple one such as in an electrostatic system or a complex dynamically varied magnetic focus system. Sharp electron beam focus is easier if optical focus has already been done. Be sure to perform an adequate first optical focus prior to fine tuning beam focus.

You have also seen the word "astigmation" mentioned in regard to beam focus. Astigmation further shapes the electron focusing lens beyond regular focus controls and is important for achieving maximal beam focus. However, it should be fairly well set at the factory and new comers to CRT setup are best advised to avoid attempting CPC magnet astigmation adjustments until they are more familiar with projection CRT setup. For this reason I will cover astigmation last in this document even though it should actually be performed PRIOR to electron beam focusing adjustments.

--------

Focusing Lens Cap to Assist with Electron Beam focusing

The phosphor grain optical focusing technique largely eliminates the need for this trick, but I mention this for completeness. Some projectors come with a special lens cap having a central hole approx 1 inch in diameter. This is intended to reduce the aperture of the optical lens and allow examination of beam focus even when optical focus is not quite correct. Because the phosphor technique easily achieves good optical focus independent of beam focus, I recommend setting the optical focus using the phosphor grain technique rather than resorting to a focusing lens cap.

--------

Electrostatic Beam Focus

Electrostatically focused CRT projectors have their electron beam focus adjusted using variable resistors aka pots. These adjust the charge on the focus lens for each gun. Focus controls are often housed together and marked as focus for each color gun. On that same housing may also be "screen" controls which adjust G2 voltage. It is easy to inadvertently adjust the screen controls while attempting to adjust beam focus. I recommend that the novice cover screen controls with a taped on piece of cardboard to avoid accidental adjustment while attempting beam focus.

Check Beam Astigmation

Display a dot pattern on the projector. Work with only one gun on at a time and set contrast to moderately high level. Binoculars are once more useful in observing the effects of your adjustments. As you vary the focus pot setting, notice how the dots change between the overfocused and underfocused directions of focus adjustment.

The overfocused state changes the dots into a central bright core with a halo around it. Ideally the bright central core is exactly centered in the halo. Also the dots should move very little as focus is adjusted between over and underfocused states.

The underfocused state changes the dots into a uniformly lit blob. Ideally the blob is perfectly circular in shape at screen center. It is normal for some deformation to be present at screen periphery.

If you find the bright core off center, the blob isn't circular at screen center, or the dots move as you adjust focus, astigmation for that gun needs to be corrected. That is done using the CPC astigmation magnets on the neck of each gun. CPC magnet adjustments should only be handled by a technician or very advanced user. Great caution is required due to risk of electrical shock, death, and equipment damage. Novices should enlist the aid of a technician if astigmation problems are noted on an electrostatically focused machine. On electromagnetically focused machines, there are often safe user accessible astigmation controls, suitable for the non-technician.

Once correct astigmation is verified (or you have decided to live temporarily with poor astigmation), proceed with the actual focusing of the guns. On an electrostatic machine it is simple.

a. Display a fine detail focus pattern or a dot hatch pattern . Set contrast to a medium level.

b. View only one gun at a time and adjust that gun's focus pot for best overall focus. It is often impossible to achieve perfect beam focus throughout the entire screen. The screen edges are particularly problematic. Should that be the case, weigh the screen center as most important for your compromise setting. That is where most film material will be sharply focused.

The blue gun electorn beam is usually left slightly underfocused to allow better grayscale tracking at higher light output levels. If you have light metering capability, that means underfocusing the blue gun enough to increase blue light output by about 20% over the fully focused state. Note that this does not mean the blue gun OPTICAL focus should be left blurred. Just the electron beam focus! They are not the same.

-------------------
Electromagnetically Focused Projectors

EM focused projectors populate the pinnacle of projection CRT technology. These machines use a magnetic coil to focus their electron beams. This is often combined with a system for dynamically varying focus to achieve good center and edge focus. (This is also done on some electrostatic machines, but not with adjustability) The EM focused projector also usually has some form of dynamic astigmation controls to refine beam spot shape throughout the screen. These extra dynamic focus and astigmation controls allow very fine focus compared to electrostatic units, but more controls means greater effort to achieve final results. EM focus also induces some spiral geometry distortions which need to be counteracted. The novice can do it successfully, but more work is needed to get everything in order.

Fore and aft sliding of the focus coil and rotation of the dynamic astigmation coils are not covered in this document. Those are maneuvers safest left to experience hands.

EM focused projector typically include a remote operable control control for overall (aka center) beam focus. This is analogous to the focus pot in an electrostatic focused machine. An EM focused machine also usually provides additional controls for fine tuning beam focus at the image edges, corners or screen zones. These extra controls allow better edge to edge beam focus than just a fixed single focus control setting.

The EM focused machine also adds a mechanism for dynamically correcting beam astigmation for each portion of the image. Dynamic astigmation refines overall beam focus beyond that achievable with just static CPC magnet astigmation. Again a control is supplied for adjusting overall astigmation (center of screen usually) and other controls for each edge, corner or zone of the screen.


Check Static Beam Astigmation

The machine will usually have some sort of CPC magnet assembly for rough static adjustment of beam astigmation. If the CPC magnets are properly set, the dynamic astigmation system won't have to work as hard to achieve good astigmation. For this reason, it is a good idea to verify and adjust the CPC magnets are properly set by neutralizing all the dynamic adjustments and then checking static beam astigmation. If the underlying static astigmation is flawed, the CPC magnets should be corrected prior to performing dynamic astigmation. The complete set of CPC magnets may not be present in a EM focused machine. Consult your service manual. Once static astigmation is done as well as possible with the CPC magnets, fine tune with the dynamic astigmation system.

Set all dynamic astigmation controls to neutral to eliminate the effects of the dynamic astigmation system.

Display a dot pattern on the projector. Work with only one gun on at a time and set contrast to moderately high level. Binoculars are once more useful in observing the effects of your adjustments.

As you vary the center EM focus setting, notice how the dots change between the overfocused and underfocused directions of focus adjustment.

The overfocused state changes the dots into a central bright core with a halo around it. Ideally the bright central core is exactly centered in the halo. Also the dots should move very little as focus is adjusted between over and underfocused states.

The underfocused state changes the dots into a uniformly lit blob. Ideally the blob is perfectly circular in shape at screen center. It is normal for some deformation to be present at screen periphery.

If you find the bright core off center, the blob isn't circular at screen center, or the dots move as you adjust center beam focus, astigmation for that gun needs to be corrected. That is done using the CPC astigmation magnets on the neck of each gun. CPC magnet adjustments should only be handled by a technician or very advanced user. Great caution is required due to risk of electrical shock, death, and equipment damage. Novices should enlist the aid of a technician if astigmation problems are noted on an electrostatically focused machine.


Dynamic Astigmation

Once static astigmation has been adjusted with the CPC magnets, one can proceed with dynamic astigmation. Some projectors will automatically underfocus and overfocus the electron beam appropriately when astimation controls are engaged. If yours does not do so, manually set beam focus to be underfocused or overfocused as needed. See the later section on CPC Astigmation for details of over vs underfocused beams with regard to astigmation.

Display a dot pattern and set contrast moderately high.

Start with all astigmation controls neutralized (center, all edges, corners, or all zones).

Adjust center astigmation skew and height controls to make the center blob circular. The machine may also have dynamic equivalents of the 2 pole adjustment. Adjust that to make the central spot centered in its halo. The actually set of dynamic astigmation controls vary from model to model, but the sequence is to perfect the center astigmation first. Then do the edges and finally corners of the screen. Zones interact so go back and fine tune when done the first time.

EM Beam Focus

Once astigmation is completed, electron beam focus can be done while viewing a fine crosshatch or focus pattern. Again, start by neutralizing focus controls for center, edges, corners or all zones. Focus the center of the screen first. Then do each edge and finally the corners. This particular order allows the interaction of the edge controls to do some of the corner correction before using any corner adjustments. Once more, recheck overall beam focus and retouch as needed.

The goal of adjusting beam focus is not only to minimize electron spot size but also reduce the flare around the spot as much as possible. Any flaring will cause edge transitions to appear soft. You will create an overall sharper looking image by accepting a slightly larger spot size if doing so eliminates the flare. Overfocus the beam and then slowly back off the control to allow the flare to diminish. Leave the control at the point at which flaring just disappears. You may need to perform this adjustment with contrast turned up enough to show the flaring. This optimizes the projector for best sharpness but not necessarily best resolution. The dot size may end up slightly larger and reduce resolution, but the increased sharpness will usually make the overall image look better defined.

This concludes beam focusing for EM projectors. I have condensed the process. The reader will best find the particular controls for his machine in the service and setup manual for the machine.


-----------------------------------------------------------------------------
3 X 5 CARD OPTICAL FOCUS TECHNIQUE

At this point in the process, both beam and optical focus should be excellent, but further refinement is sometimes possible.

Use a plain white 3 x 5 card for finding the exact focal distance of the projector. Do this by moving the card fore and aft in front of your screen to see at where a fine focus pattern is best in focus. If it is already exactly at the screen surface plane throughout the screen, then you are done. If it is more than 1 cm in front of or behind the screen do the following. And yes, this will temporarily undo the hard work done getting the phoshor grain sharp.

Display a fine detail focus pattern (internal focus pattern or S&V Home Theater Tune-Up) and intentionally overfocus the optics (rear lens control) so that the center is best optically focused about 2 cm short of the screen. This is in the direction that extends the lens barrel forward. Bringing the focal plane slightly short of the screen lets you more easily examine the focal distances throughout the image area. Check the focal distance for each screen edge by moving the 3 x 5 card back and forth in front of the screen. You'll be able to see very accurately the distance at which things are best focused on the 3 x 5 card. Check if the distances are uneven between left/right (indicating a horizontal lens flapping error) and top/bottom (indicating a vertical lens flapping problem). Fine tune lens flapping to make the focal distances for top = bottom, and left = right. This is the time to fine tune lens flapping rings. The 3 x 5 card check is so precise that you'll notice the flapping changes caused by uneven tension on the lens mounting screws.

Next, pay attention to how the left and right edge distances compare to the distance at screen center. They should be about equal between center and edges. If not, slightly adjust the inner and outer optical focus to bring both the edges and center to focus about 2 cm in front of the screen. Notice that I don't have you check the screen corners. That is because there will almost always be a difference in the extreme corners and center and using the left/right edges gives a good compromise which preserves the central focus where the video image is going to be sharpest portion of a movie frame anyway.

At this point the optics are perfectly balanced in terms of Scheimpflug and inner vs outer lens focus. The next step is to shift the entire optical plane back onto the screen surface. Make tiny movements of the rear lens focus knob while repeatedly checking the optical focus position with the 3 x 5 card. One thing to consider is that you probably did all this with the projectors lens hood off and the lenses are a little cooler than normal. As the lenses warm up, their index of refraction decreases, the lens mounts expand, and the focal plane can move slightly inward or outward. You should recheck the focal plane when the optics reach normal operating temperature an hour or so after the lens hood and hushbox are closed. Also, recheck 24 hours later and compensate for mechanical settling.

If you use the 3 x 5 card for final optical focus, you'll note that it is so sensitive an indicator that even the slight shift of the lens while tightening the focus knobs will be detectable. Focusing a projector is an iterative process in which improvement in either optical or beam focus enable finer observation and adjustment of the other focus system. Patient and diligent technique is needed to achieve maximal sharpness of both optical and beam focus systems. Expect a great deal of exercise moving between screen and projector using this technique.

Perfected optical focus means that even better beam focus may be possible. Revisit beam focus and fine tune as appropriate.

Only AFTER both optical and beam focus are perfected should you do final work on geometry and convergence can proceed. Otherwise, geometry and convergences changes wrought by focus adjustments will upset a hard gained geometry and convergence setup.

Speaking of which, the next steps in projector setup would be

Rough geometry and convergence
Grayscale calibration (with possible blue gun defocusing)
Final geometry and convergence

Those next steps are not discussed in this article.



===========================================================

------------- Advanced Setup Technicians Only ------------------

CPC Magnet Adjustment of Beam Astigmation

Warning!!!!! Novices and non-technicians are warned to avoid performing astigmation CPC magnet adjustments. Adjustment of CPC magnets should ONLY done by advanced setup personnel. Improper technique will render focus impossible. High voltage shock and tube neck fragility are also significant hazards during CPC magnet adjustment!!!!

Electron beam focusing lenses are not perfectly uniform. Also, the direction of the earth's magnetic field can cause the beam to enter the lens off center. Astigmation of the beam fine tunes the lens uniformity and centers the beam as it enters the lens. This allows the beam lens to create a small electron spot with minimal flaring. Poor astigmation can make good electron beam focus impossible.

Static electron beam astigmation is carried out using CPC magnets (called Color Purity Control for historical reasons) on the tube neck and/or electronic astigmation controls. If both CPC magnets and electronic "dynamic" astigmation controls are present, it is best to let the CPC magnets do most of the work and have the electronic astigmation system merely fine tune the effects. One must neutralize the electronic astigmation controls prior to adjusting CPC magnets.

CPC magnets are arranged as pairs of rings about the end of tube neck near the socketed drive board. They should not be confused by the much more forward raster centering magnets just behind the deflection yoke. Projectors don't always have the full set of 2, 4, and 6 pole CPC magnets. CPC magnet assemblies vary in appearance and mechanical design. Sometimes the ring pairs have a small knob allowing one to adjust the angle between the two rings of a pair. More often one merely sees tabs with which to manipulate the rings. The CPC have 2, 4, or 6 magnetic poles, but don't confuse that with the number tabs on the rings. One cannot actually see the poles. By varying the angle between the two rings of a pair (moving tabs in opposite directions or twisting a little knob) one varies the intensity of the effect. Rotating a pair about the axis of the tube neck (moving tabs in same direction or twisting little knob in opposite direction) changes the directionality of the effect. If all three sets of CPC magnets are present, the rearmost is the 2 pole (centering). The middle is the 4 pole (ovalness). And the most anterior (if present) is either non-functional or a 6 pole correction (triangularity).

I'll reiterate since this seems to confuse some people....

Intensity: The amount of effect that a magnet ring pair creates. For instance if you consider the two pole magnet pair, you can make the rings cancel each other out or augment each other by varying the rotation of the two rings relative to each other.

Directionality: The orientation of the net magnetic effect. If you spin a ring pair TOGETHER around the tube neck you spin the direction in which the poles affect the electron beam. Notice that this minimally changes how the poles cancel or reinforce each other. Spinning the pair together merely lets you vary the direction in which that magnet ring pair squeezes or expandes the beam.

Spinning a pair together changes the direction of the effect, but making the two rings of a pair spin in opposite directions changes the amount of their effect.


Because the factory performs CPC magnet alignment, shipping can shift controls, and end users are not expected to make these adjustments, the CPC magnets are usually held in place with some silicone adhesive. This must be removed carefully. Very cautious picking at the adhesive with fingers will usually free the controls. Do not mechanically stress the tube necks!

Again, neutralize all electronic astigmation controls prior to working with CPC magnets. On projectors which lack separate electronic astigmation controls, perform CPC and electronic astigmation while the highest scan frequency to be used is displayed.

I assume you know how to change the electron beam focus and don't get that confused with optical focusing.

The 4 Pole (middle) CPC magnets affects ovalness of the electron beam lens. Adjust this while displaying a dot pattern with contrast set moderately high. Intentionally UNDER focus the electron beam making the dots into uniform blobs. Adjust the 4 pole magnets to make the center blob as perfectly circular as possible. Physically walk up to the screen to judge shape. Turning the small knob or moving adjustment tabs in opposite directions alters the amount of ovalness. Spinning the 4 pole rings around the axis of the tube neck changes the direction of the ovalness axis.

The 2 Pole (rear) CPC magnets centers the electron beam in the electron beam lens. Adjust this while displaying a dot pattern while contrast is moderately high. Intentionally OVER focus the electron beam making the dots into a flare with a bright central core. Turning the small knob or moving adjustment tabs in opposite directions alters the amount of deflection. Spinning the 2 pole rings around the axis of the tube neck changes the direction of deflection. Make the bright core centered in the flare.

The 6 Pole adjustment is also done with the dots pattern in under focus. If the 6 pole works (it may not do anything) it creates a triangular astigmation change. Use it to correct any residual triangularity which you could not correct using the 4 pole.

Go back and forth between the 2 and 4 pole adjustments to get things right. As a final check, carefully watch the dots as you go from under to over focused. The dots should stay almost motionless as you vary the beam focus. If they move, redo the 2 pole adjustment.

Once CPC magnets are set, fine tune using electronic astigmation if available.

You will have to redo raster centering after adjusting the CPC magnets. If working on the blue gun, you'll probably want to leave the electron gun underfocused enough to make its light output measure about 20% higher than its fully focused state to improve grayscale tracking at higher light output.

Guy Kuo
Guy Kuo is offline  
post #9 of 163 Old 12-08-2001, 09:18 AM
AVS Special Member
 
jcmccorm's Avatar
 
Join Date: Mar 2001
Location: Madison, AL, USA
Posts: 3,370
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked: 13
Guy, as always, thank you VERY much for your time and expertise. The information you share is priceless.

Cary
jcmccorm is offline  
post #10 of 163 Old 12-08-2001, 10:46 AM - Thread Starter
AVS Special Member
 
stefuel's Avatar
 
Join Date: Apr 2001
Location: Marshfield, MA, USA
Posts: 5,880
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 13
I wonder how many people have raided their wives recipe file cards to work on their projectors I did. Thank's Guy.

Chip S.

Current owner of the last/best AmPro on the planet. The mighty 4600HD, and it's still running...better than Barco's, especially southern ones.
stefuel is offline  
post #11 of 163 Old 12-08-2001, 05:42 PM
Member
 
Bruno Lovisi's Avatar
 
Join Date: Oct 2001
Location: Nice, France
Posts: 105
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Hello

Sorry for your NEC, it's really sad!

And thank you very much for your excellent post !!!


regards

Bruno
Bruno Lovisi is offline  
post #12 of 163 Old 12-08-2001, 10:28 PM
Senior Member
 
kawal's Avatar
 
Join Date: Nov 2001
Location: Sequim, WA
Posts: 287
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Guy,
In your EXCELLENT post, you discuss astigmatism adjustments in detail. You mention that projectors have either 2,4, or 6 rings for adjustment.
In my Sony G70, I believe there are only two rings. If I understand your discussion correctly, then these two rings must be centering rings only? In other words, adjustment of these rings will affect only centering and not focus quality. Is this correct?
If the above is correct, it would seem that the only MECHANICAL focus adjustments on the G70 would be the optical lens focusing and the flapping adjustments. All other focusing would be the magnetic focusing per the manual, and of course, your suggested techniques.
Does the above sound correct?

Thank you again, for all of the time you devote to this forum.

Ray Kawal
Sequim, WA
kawal is offline  
post #13 of 163 Old 12-09-2001, 04:46 AM
AVS Special Member
 
JonFo's Avatar
 
Join Date: Dec 1999
Location: Big Canoe, GA, USA
Posts: 1,337
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 14 Post(s)
Liked: 18
Quote:


Originally posted by Guy Kuo
I have combined some information here from several of my postings to create a more unified document.
.

Thanks Guy. This is awesome.

Next time I move the PJ/screen, I'll use these techniques.
JonFo is online now  
post #14 of 163 Old 12-09-2001, 05:53 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The single CPC magnet ring pair on the neck is a 4 pole. It is used to set the beam shape to be round while the electronic astigmation AQP, ADP are neutral. (Thanks to Steve Smith for verifying this)

This does point out one problem with discussing CPC and raster centering magnets. Not all projectors have all the magnets. Raster centering magnets are right behind the yoke but are sometimes not present. The same with CPC magnets which are near the socket end of the neck. They aren't always all there. Sometimes the controls are solely in the electronic domain rather than mechanical controls. The service manual might not even match what is physically present.

I hope that things make more sense with all the info gathered together into a document which can more or less be followed in sequence. I know it is a long procedure, but I think it's worth the effort.


[edit - paragraph moved to unified post]

Guy Kuo
Guy Kuo is offline  
post #15 of 163 Old 12-09-2001, 06:35 AM
AVS Special Member
 
mp20748's Avatar
 
Join Date: Nov 2000
Location: Maryland
Posts: 6,339
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 13
"Incidentally, if the projector does not have separate electronic astigmation memories for each scan frequency, do the CPC adjustments while the highest input frequency is being displayed."

Yep, very important point.

KUDOS!

It's all about the performance... Got Marquee!

 

High Performance Marquee Video chain modifications.  Now available!

mp20748 is offline  
post #16 of 163 Old 12-09-2001, 06:41 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Actually, I meant the full astig (both CPC and electronic) at the highest freq. I have updated the main post to reflect that point and clarify a few things.

Guy Kuo
Guy Kuo is offline  
post #17 of 163 Old 12-10-2001, 06:54 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Even if you are not moving your projector or screen, go ahead and examine the focal plane using the 3 x 5 card without first changing the lens settings. The "give" of the screen fabric will be enough to examine where the focal plane is at screen center. The edges are harder to test without pulling the optical plane out in front of the screen. If the screen is a drop screen, then it's easy to check things by moving the fabric itself.

Guy Kuo
Guy Kuo is offline  
post #18 of 163 Old 12-10-2001, 10:42 AM
AVS Special Member
 
Brian Hampton's Avatar
 
Join Date: Apr 2000
Posts: 6,669
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
Liked: 58
Hello,

Thanks for the great post.

I'm confused about step 1. You refer to the mechanical aiming of the guns and raster centering. I can't figure out what you mean. Are you refering to using the projector's shift controls to center the raster on the tube face? This wouldn't be a mechanical adjustment. Are you talking about moving the tubes themselves? How would this affect the raster position?

You also mention using a white field instead of the crosshair patterns because the internal pattern may be off-center. I think you may be refering to an internal pattern such as the warm up screen on the Sony 12xx series since this pattern is suppposed to utilize the entire face. If not, how is that step done for people without such a pattern? The remove the lens method?

If the rater centering is done like you described than it's nessasary to shim the lenses (unless they are very adjustable) to center the Red and Blue to the Greeen after the proceedure is done. I would rather stick with the factory shims and use the electronic controls to center the images at least for now so does that make the mechanical aiming a step to skip?

Thanks Very Much,

Brian
Brian Hampton is offline  
post #19 of 163 Old 12-10-2001, 10:54 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I'm talking about mechanically aiming the gun/lens assemblies so their optical centers are aimed right at the center of the screen, not simply moving the rasters about the surface of tubes that aren't actually mechanically aimed correctly.

You can skip steps, but the overall stability and precision of the setup is compromised.

Guy Kuo
Guy Kuo is offline  
post #20 of 163 Old 12-10-2001, 01:11 PM
AVS Special Member
 
Brian Hampton's Avatar
 
Join Date: Apr 2000
Posts: 6,669
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
Liked: 58
HI,

Thanks for the reply. I don't really want to skip steps, I just was trying to understand the instructions fully.

My current understanding is you can use shift/zone controls to place the centercross pattern on the exact tube center then mechanically adjust the tube/lens assemblies to place this correctly on the screen.

Thanks again for the informative post.

-Brian
Brian Hampton is offline  
post #21 of 163 Old 12-13-2001, 11:59 AM
AVS Special Member
 
Chuchuf's Avatar
 
Join Date: Jun 2000
Location: Alpharetta, GA
Posts: 5,033
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Guy,

What resolution do you generally run on your G-70??

Terry

AVS Marketplace or Videogon are the places to see F/S ads
Chuchuf is offline  
post #22 of 163 Old 12-13-2001, 12:47 PM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The main posting has been updated to explain why the aiming sequence seems backwards.

My own unit is actually an NEC XG135LC from AV Science, not a G70. I run it primarily at 960 lines on a variable height 80 inch wide screen. The equivalent on a 16:9 would be 720 lines. The scaler I use (Faroudja DVP-3000) does my AR switching so I only need a single setup for NTSC.

Guy Kuo
Guy Kuo is offline  
post #23 of 163 Old 12-14-2001, 07:56 PM
Member
 
pat*m's Avatar
 
Join Date: Sep 2001
Location: Iowa
Posts: 57
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Great Info Guy!!!
Thanks for taking the time to write this up nice and neat
pat*m is offline  
post #24 of 163 Old 12-15-2001, 09:53 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I've been recently asked about this......

Mechanical aim is not the same as lens flapping (aka Scheimpflug). Mechanical aim of the CRT/lens assembly is the same as taking a telescope and physically pointing it at something. Lens flapping is adjusting the mounting angle of the end lens without changing where the telesope is pointed.

The red and blue guns of a CRT projector have mounting screws which when loosened allow the two outer guns to swing left/right. The central green gun usually isn't adjustable left/right (another reason to be very accurate when mounting the projector) Up/down mechanical aim is accomplished by altering projector tilt.

Lens flapping doesn't change the direction of aim (by much anyway), but compensates for the planes of the screen and phosphor not being parallel. The flapping places the lens into a plane which is intermediate between those of the screen and phosphor so the entire surface can come into focuse simultaneously.

(info also added to main focus posting)

Guy Kuo
Guy Kuo is offline  
post #25 of 163 Old 12-16-2001, 02:59 AM
Senior Member
 
StephenMSmith's Avatar
 
Join Date: Dec 1999
Location: Marina del Rey, CA
Posts: 320
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Hey Guy.

I've been collecting your previous focusing tips and have applied them quite successfully to *rear* projector (well, all but mechanical aiming and lens flapping, which are the only ones that don't apply to my RPTV). Nice to seem them all consolidated and organized! The only trouble I've ever had is with the 2-pole CPC adjustment. On my RPTV, regardless of contrast level, the core and flare are just not distinct enough to effectively center the core within the flare. Maybe this is due to the short throw distances in a RPTV?

I've done the whole focusing procedure you describe above several times very successfully, except for the 2-pole adjustment, where I've always had to resort to working backwards, ie. searching (almost randomly) for some position that minimized dot movement when rotating the focus VR through it's range. But last week I downloaded a service manual from some other manufacturer and found a simple 2-pole method that worked perfectly for me, and finally allowed me to achieve *no* dot movement instead of settling for just minimal dot movement.

I marked the exact center of my screen and then used AVIA's center cross pattern, which has a convenient little dot right at the cross intersection. Then I just went back and forth b/t the 2-poles and centering magnets, using the centering magnets to center the dot in the extreme underfocused state and the 2-poles to center the dot at extreme overfocus. After only a few iterations of this I had a nice dots pattern with absolutely no movement at all throughout the focus extremes. Do you have any comments about this method?

Also, one thing I've always wondered: I have 6-pole magnets on my yokes but they are non-functional according to Toshiba tech support. OK, how can the 6-pole magnet pair be placed on the yoke and yet still be non-functional? Is there some other yoke component required somewhere to make them functional?


Thanks,

Steve (not to be confused w/other Steve Smith (Advanced Member) I see posting above...)
StephenMSmith is offline  
post #26 of 163 Old 12-16-2001, 06:55 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I think your method for setting the two pole should be fine if you are able to get zero motion with focus changes. It sounds from your description that you may be doing this on an RPTV with the screen mounted on the television. You will have an easier time seeing the core and flare if you take the screen off and look directly into the lenses of the CRT's. Give it a try. It is easier to set 2 pole if you can observe the core and flare.

The 6 pole magnets on the set cannot have zero effect unless they are physically present but not magnetized. In effect, unmagnetized poles would be duds.

Guy Kuo
Guy Kuo is offline  
post #27 of 163 Old 12-16-2001, 06:58 PM
Senior Member
 
StephenMSmith's Avatar
 
Join Date: Dec 1999
Location: Marina del Rey, CA
Posts: 320
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Ah ha. Yes, I was doing astig & alignment w/the screen on. With one hand on the magnets and the other at the focus VR, I'm starting at the screen from like 8" away, where everything is going to be fuzzy to say to the least.

One other question about non-magnetized 6-poles: if they're non-functional, why do they bother to even put them on the yokes? The CRT manufacturer just puts them on by default on all their CRT's, and then the set manufacturer chooses whether or not to magnetize them?

Steve
StephenMSmith is offline  
post #28 of 163 Old 12-17-2001, 10:08 AM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The poles would have to be magnetized before the CPC assemblies were put together, so I'd bet they were ordered as duds and simply never magnetized. The triangular correction is probably one less thing to set up during display assembly at the factory. Less setup time means less cost.

I'd bet this is why we are seeing sets now which have a single scan frequency and use a scaler to convert everything to the same scan frequency instead of changing raster sizes and scan frequencies. You only need your workers to set up one convergence memory at the factory. One just needs a built-in scaler good enough to satisfy J6P.

Guy Kuo
Guy Kuo is offline  
post #29 of 163 Old 12-17-2001, 01:41 PM
Senior Member
 
StephenMSmith's Avatar
 
Join Date: Dec 1999
Location: Marina del Rey, CA
Posts: 320
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Well if I could magnetize them, I would. I don't mind one more thing to set up .


One other question for you, Guy:

Can the phosphor grain focus technique work for RPTV's? I'm guessing that this surface grain will be far too fine to actually see through my frensel/lenticular screen stack?


Steve
StephenMSmith is offline  
post #30 of 163 Old 12-22-2001, 11:14 PM
AVS Special Member
 
Guy Kuo's Avatar
 
Join Date: Feb 1999
Location: Seattle, WA
Posts: 3,172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
The lenticular and fresnel layers on an RPTV do make for a fairly coars screen compared to a good front projection fabric. Even Dalite's moderately speckled fabrics can interfere with seen the grain so no I don't think the phosphor grain method is as applicable to RPTV's. Better to use the "cantilever technique" by Mr. Bob. http://www.keohi.com/keohihdtv/index.htm

Guy Kuo
Guy Kuo is offline  
Reply CRT Projectors

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off