[Graham Johnson]

Is blue focus always the most difficult on all these projectors ?? it always seems the dimmest.


There is a halo around the spots on the in built test pattern butn only on the blue tube.


Ideas please ????


Thanks Graham

 

[stefuel]

What kind of projector is it or what tubes does it have. I've got a sneaky suspicion you have Sony 07MS or SD-187 tubes.


Chip S.

 

[Graham Johnson]

VPH 1041,


Not sure what tubes it has in it ???


Graham

 

[shanemac]

... I had the same problem on my 9pg ...until I flicked the switch for the de-focus blue off.

 

[Graham Johnson]

Thts bizzare why would you ever want to purposely defocus blue ???


Graham

 

[Guy Kuo]

Defocusing of the blue gun is pretty commonly used to increase blue gun output. It allows a greater total light output while still maintaining good grayscale tracking. If the blue gun is fully focused, the maximum light level at which one can still maintain good grayscale tracking drops by about 20 to 30% Since the human eye is relatively poor at resolving details in blue light, the resultant degree of image softening is much less than would be expected. Overall, blue defocus is a good trade-off in light output starved CRT projectors.

 

[Graham Johnson]

Guy, is this normally adjustable ???? It is so bad that its distracting.


When I focus the green and red guns I can distinctly see the scan lines when I get the best focus at 576i.


The blue is just a haze and the scan lines are invisible in that haze.


When you put up the dot test pattern the hot centre of the dots on 100 inch screen are about 1/4 of an inch round but the haze is about 3/4 of an inch round.


Graham

 

[Guy Kuo]

Sounds like your blue gun is more defocused than normal. Yes, it is adjustable. It is tougher to see the focusing of blue and pick apart the difference between optical and beam focusing problems. One thing you can do is look directly into the blue gun lens while adjusting beam focus. Some sunglasses might be helpful. Looking directly into the blue lens will let you see the beam focus independent of the optical focus. The beam focus should be able to get nearly as sharp as the other guns on a properly working system. (Not that you would necessarily leave it fully focused) Once you get blue beam focus as good as possible, then redo the optical focus.

 

[Curt Palme]

I'm thinking blue tube fungus...


Curt

 

[Graham Johnson]

The weird thing about this. is that I had a very good (for this projector) image when I had it temporarily set up on a table. But now I have placed it in it's final position, inverted hanging from the roof. The blue seems significantly worse in focus and harder to converge. Some of the blue convergence controls are way off to one side. (wasn't like that set up on the table)


It does have a small smudgy stain inside the liquid chamber, but the odd thing is that it wasn't a problem until I inverted it. I suppose I may have become more critical since i put it in its final position.


I have also noticed that the focusing of all tubes seems much harder inverted than the right side up.


Comments

 

[Curt Palme]

I can't explain that either, but if it's really out of focus within that 'stain ' area, that's fungus.


Curt

 

[Tom Morrow]

On my Sony 1272 I can't get the electrical blue focus as tight as the red or green focus. Even when I have it focussed as tight as possible the blue spot width is almost twice as wide as that of the green. I just accepted it since the blue defocussing is useful for the reasons that Guy mentioned.


Three times as wide might be a sign of problems or it might not. I wouldn't dwell on it until you get everything else set up and if it is noticeably bad on actual images then maybe reconsider. Then again the smudging you mentioned doesn't sound good!


-Tom

 

[cybrvanr]

Quote:

The weird thing about this. is that I had a very good (for this projector) image when I had it temporarily set up on a table. But now I have placed it in it's final position, inverted hanging from the roof. The blue seems significantly worse in focus and harder to converge. Some of the blue convergence controls are way off to one side. (wasn't like that set up on the table)

Looks like the blurryness is coming from bad liquid cooland. The glycol coolant that goes on the face of the CRT between the lens. When you inverted the projector, some of the fungus and other grime that was out of sight got circulated into the line of sight.

 

[Graham Johnson]

Last night I'd had enough, and basically started from scratch.


I removed the lens and had a good look at the raster and noticed it was actually somewhat closer to the bottom of the tube face than the top.


I got a ruler and measured it from the top and and bottom and cetralized it on the tube face. I then slightly reduced the width of the scans, incase the focus problem had anything to do with badly ground lenses at the edges (a common fault).


Centralized all the convergence adjustments.


Screwed the lenses back on.


Apart from slight central registration problems, the picture was almost converged already.


Went through focus again. and noticed that even when I had arrived at the best edge focus possible the actual edge focus on a white card was actually still some distance (4 inches) in front of the screen. But it does look better.


Spent the next two hours getting it right and it is now quite good.


Just getting back to this blue focus issue it was pointed out that this is intentionally done to increase light output. Well I recon I have too much and can't find a control to tweak it down. anybody got a service manual for a VPH 1041/42/44 that can see if its adjustable ??


Thanks every one


Graham


P.S. I can just see what the blue smudge does during blue focus it's actually not too bad and only affects about 1/8th of the screen. I'll leave it for now.