CurtPalme.com Home Theater Forum

nj89 · Joined: 17 Jul 2017 Posts: 2

I've got my g90 on the ceiling at this point, and this weekend I ran through a full alignment. After having completed this, I have a number of questions.

Questions:

1) Schiempflug.

I followed some advice I found online that I think originated from Guy Kuo. I deliberately defocused the electron beam, and then displayed a solid pattern and worked to image the phosphor grain onto the projector screen. I was very successful with the green, but found the red and blue phosphor grain was not perfectly imaged across the whole screen. Am I doing something wrong here, or is this unavoidable? I think this is occurring because the red and blue lens are not perfectly centered L/R with respect to the screen. Thoughts?

2) Electronic focusing.

Displayed a dot pattern, and set the 2 pole (H and V) so that the central dot does not translate left/right or up/down as I adjust electronic focus. Then I set the 4 pole so that the dot looks maximally symmetric/circular as I adjust electronic focus, and then the same for the 6 pole. My problem with this method, and it is especially pronounced for the 6 pole, is that there seems to be a huge parameter range where the defocused dot looks very circular. For the 6 pole I'd say everything looks the same to my eye for at least a full quarter of the range (full range is nominally 0 to 256). I feel like I am not making the most of this adjust. Are there better methods?

3) Electronic focusing off of center.

There were four adjustments per off center position, and I had no idea what they were doing... I'd scan the full adjustment range without being able to discern ANY change in the dot pattern. Is there a systematic way of going about setting these values?

**Curt Palme** · Posted: Mon Oct 23, 2017 5:59 pm Post subject:

For the focusing around the outside edges, yes, they have less effect than the centre adjustment, but they should still have some effect. Is the contrast at 100%? That's how you'll see it the most.

Second, use the 'EM' focus test pattern. It's much easier to see blurring than using the dots or crosshatch.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I defocus OPTICALLY when adjusting scheimpflug. I adjust so that the width of the defocused grid bars is equal. Then refocus.

I have found that to be a highly successful technique.

Also, do scheimpflug with 4:3 aspect ratio source material and actually the wider and taller the image is, before it runs off the
edges of the CRT, the easier it is to properly adjust scheimpflug as well as every other outer zone adjustment.

nj89 · Joined: 17 Jul 2017 Posts: 2

Alright! Thanks for the tips.

Curt - I had been using dots - will switch to the EM focus pattern and see if I can make better use of the adjustments/detect any change in the outside adjusts. Also, I think contrast was turned way down, maybe minimum, when doing the EM focus. Will try with max contrast.

cmjohnson - I will try the optically defocused schiempflug adjust. I'll try on green and see if the phosphor grain ends up being imaged automatically. If so, I'd say the technique is better, if not, it's probably not as good (but perhaps faster?). And yes, I have been adjusting using an almost full raster, and then squeezing the vertical down to achieve 16:9.

Will report back once I've tried all this stuff out.

**Curt Palme** · Posted: Wed Oct 25, 2017 2:38 pm Post subject:

You'll find that you get much better results at max contrast. Just don't leave the test patterns up on the screen for hours on end, in fact I wouldn't work on one tube for more than 20 minutes at a time. Switch to a different tube, then go back. That gives the phosphor time to recover, preventing burn-in.