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Mastering the scheimpflug adjustment

 
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cmjohnson



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


PostLink    Posted: Sat Apr 01, 2017 1:42 am    Post subject: Mastering the scheimpflug adjustment Reply with quote


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Just a reminder for those who don't know about this, but there is an easy to get your scheimpflug (lens flapping) adjustments perfect that's actually very simple.

Defocus the lens being adjusted. Adjust scheimpflug so that the blurred grid lines are of equal apparent width from end to end.

I honestly can't remember how long it's been since I remember even reading about this, or even if I ever did, but it works
so well that the scheimpflug adjustment guide should START with "Defocus the lens!".

I hadn't done that since I re-hung my rebuilt Marquee Ultra. It was looking quite good and sharp, but I just redid scheimpflug using this method and the difference in corner to corner sharpness is quite noticeable. The picture is simply awesome, sharp and detailed, and I'm loving watching movies tonight.

If your machine is not quite at its full sharpness, do take the time to tweak everything to the max. It makes more of a difference than you might realize.

I maintain that the finest final adjustments to a CRT projector make a disproportionate improvement to the overall picture quality.

If your grid lines aren't as thin and clean at the ends as they are in the middle of the screen, you've got work to do.
Readjust focus, scheimpflug, and astig.

I was ready to admit that my JVC D-ILA (RS45) was really sharper than my Marquee Ultra in every meaningful way,
but now that I've re-tuned the projector and lenses to be as sharp as is possible, I can no longer honestly make that claim.
The Marquee is now as sharp as the digital projector in any way that really matters. And the blacks on CRT are still better!

I have the JVC's aperture turned way down and it still slightly illuminates the screen with no signal applied. I have the
Marquee's black levels adjusted so that with no signal you can't see the screen at all in a fully darkened room, and yet
when comparing shadow details, the Marquee gives up no ground to the JVC.

Now if only I had a cheap solution to getting rid of the raster ringing along the left side edge of the Marquee's picture....

I can do it by setting retrace to long but that results in an offset picture that's too wide and goes into the blanking area.
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AFryia



Joined: 09 Mar 2006
Posts: 931
Location: S.E. Michigan VPH-G70Q


PostLink    Posted: Sat Apr 01, 2017 9:00 pm    Post subject: Reply with quote

My approach borrows from Guy Kuo's white card focus technique; is isolated to the glass optics so immune to any potential electronic hardware or electronic setup issues.

1) display a white/grey screen, then display one tube at a time. (electronically de-focus all tubes to eliminate scan lines)
2) adjust center focus so the phosphor grain comes into focus 12 inches in front of the screen displayed on the white card stock.
3) using the white card check how far off the screen the grain comes into focus on the left and right sides of center.
4) adjust scheimpflug to balance the left and right distance to the screen. Take note it may be different than center focus, that's OK.
5) using the white card check how far off the screen the grain comes into focus on the top and bottom of the screen at center.
6) adjust scheimpflug to balance the top and bottom distance to the screen. Take note it again may be a different then the center focus.
7) check the grain focus distance at the corners and adjust corner optical focus to equal center as close as possible. Not all 4 corners will be equal.
8) adjust center focus so the grain is now 4 inches off the screen.
9) check and adjust if necessary the left/right and top/bottom scheimpflug to match the center distance.
10) if necessary tweak corner focus using the grain.
11) adjust center focus until the phosphor grain comes into focus on the screen.

The grain for left,right,top,bottom, and corners should also focus on the screen but not necessarily as sharp as center; it depends on the quality of your lenses and PJ angle. You can try and tweak left,right,top,bottom, and corners if you wish. If things get out of control just move the grain back off the screen ~4 inches and re-work the left,right,top,bottom, and corners.

cheers!

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cmjohnson



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


PostLink    Posted: Sun Apr 02, 2017 11:04 am    Post subject: Reply with quote

I just got back from a job where I had to retube and set up 30 Marquees in three weeks. If I were using the white card/phosphor grain approach I'd still be there. Defocusing and adjusting for equal width blur across the length of the grid line should yield the same results anyway and it's extremely quick and rather precise.

They weren't going into a home theater environment anyway.
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kal
Forum Administrator


Joined: 06 Mar 2006
Posts: 16286
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Sun Apr 02, 2017 1:30 pm    Post subject: Reply with quote

AFryia wrote:
My approach borrows from Guy Kuo's white card focus technique


FYI - I have Guy Kuo's entire procedure here: http://www.curtpalme.com/Focus_and_Mechanical_Aim1.shtm

Kal

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cmjohnson



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


PostLink    Posted: Sun Apr 02, 2017 1:38 pm    Post subject: Reply with quote

The point of my method is that it helps get you really, really close if you find that you're getting kind of lost in the scheimpflug adjustment. I know a lot of people have had difficulty with it, and I have found that defocusing and looking at the width of the defocused grid lines while making the adjustment makes it a lot easier to understand where you are at and where you need to be.

I do agree that the phosphor grain and white card approach is a good way to absolutely nail it to perfection, but it's helpful to get
it close via my method first.

Scheimpflug is particularly problematic if you're not running a 4:3 aspect ratio. And who does that? The less height there is in the
picture, the harder it is to get the vertical scheimpflug adjustment ironed out right.

I would add, for that very reason, that it is very helpful to do your scheimpflug adjustment with your raster size maximized both horizontally and vertically even if that takes part of the image off your screen. This isn't actually a bad idea when making zone adjustments of ANY kind. You may have to strategically place pieces of paper near the screen to give you some temporary screens to adjust on, of course.
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AFryia



Joined: 09 Mar 2006
Posts: 931
Location: S.E. Michigan VPH-G70Q


PostLink    Posted: Mon Apr 03, 2017 11:15 pm    Post subject: Reply with quote

cmjohnson wrote:
I would add, for that very reason, that it is very helpful to do your scheimpflug adjustment with your raster size maximized both horizontally and vertically even if that takes part of the image off your screen. This isn't actually a bad idea when making zone adjustments of ANY kind. You may have to strategically place pieces of paper near the screen to give you some temporary screens to adjust on, of course.
Too funny! I did exactly that Laughing Laughing

I taped white cards to 1 inch thick styrofoam and two-way taped them to the wall where the 4:3 the corners would be found just off the 16:9 screen. I only used them for the initial registration of the various memory blocks. I found those corner references very helpful when adjusting PIN, BOW, CENT.

I thought I was the only OCD CRT'er.

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