CurtPalme.com Home Theater Forum

Rattanee · Joined: 18 Jan 2015 Posts: 193

Hey guys,

I'm curious if anyone can point me in the right direction regarding lens-flapping and PJ positioning for horizontally off-center projector placement?

I want to have multiple (namely three) PJs set up to project on the same screen, and I am curious how to properly set up and align the projectors next to the center one.

Projector placement seems like the first curious problem, as adjusting lens flapping will alter the center point of the projected image coming from the CRT being adjusted, and since the green CRT cannot be moved (toe-in), precision mounting seems essential. Is there a specific set of formulas I can find somewhere for calculating possible mounting angles, or do I just break down and "do the math" based on the scheimpflug principle ?

It all seems to be in the placement really, as once mounted correctly, adjusting proper flapping is comparatively easy.

gjaky · Joined: 05 Jun 2010 Posts: 2802 Location: Budapest, Hungary

Side by side setups on the same screen eats V-keystone, this is something that CRT projectors don't like. You'd be better with 3 projectors stacked on each other.

Rattanee · Joined: 18 Jan 2015 Posts: 193

I plan on putting up the PJs with less then perfect tubes on the sides, so I'm not really worried about tube wear (green tube is about a 7 on one, a 5 on the other...), and they would be pretty close to each other to minimize keystoning as much as possible (have maybe 5cms between PJs tops) The idea is to have the 'best' of the lot in the center, exclusively for HD content, a second HD capable set for PC/PS gaming (with more used tubes so that I won't be afraid of burning the phosphor Razz

) and a small sony set exclusively for classic gaming (JAMMA boards, retro consoles, what have you).

I'm also modding the cooling on all the PJs for less noise and more effective cooling, so that little keystone shouldn't be a big problem.

**Curt Palme** · Posted: Mon Nov 02, 2015 1:22 am Post subject:

I have two Barco 909s separated by about 3' (1m) in a stack on a 10' wide screen. No issues at all, but of course the Barcos have the most keystone adjustment as they are meant to do that. Cliff had two g90s side by side and no issues either. Lens flapping will allow for correct focus for sure, so no problems there either.

mc86 · Posted: Mon Nov 02, 2015 1:41 am Post subject:

To get three side-by-sides shooting on one screen with the same center, you MUST either make the green tubes able to be toe-in adjusted OR have to angle the front axis of the side machines. In either case, do you have the controls in your PJ to adjust the greens independantly like the red and blue? On my old ECP anyway, green controls are more limited and blue and red get set to green...

The correct angle for lens flapping is always the same: Determine the angle defined by the plane of the tube face and that of the screen...I'll call this angle 1. The plane/line perpendicular to the main axis of the lens assembly (parallel to the lens face) must bisect (be half of) angle 1. I suppose if your angle is too severe, you won't have the mechanical wiggle-room to achieve this with the lens. Alternatively/Additionally, you might run out of electronic adjustment, too. To give you more freedom, your choice would be to locate the CRTs further from the screen...of course size becomes a trade-off at that point.

If precision mounting/location is the idea, why not fix to the floor some locating pins or guides of some sort (hallows the feet/wheels could sit in, perhaps?) and then shuffle the machines between locations on some casters. You'd be able to align a machine within a few minutes to within a few millimeters, I'd bet. Wink

Matt

**Curt Palme** · Posted: Mon Nov 02, 2015 1:54 am Post subject:

Ratt, what is the projector model?

Rattanee · Joined: 18 Jan 2015 Posts: 193

Rattanee · Joined: 18 Jan 2015 Posts: 193

**Curt Palme** · Posted: Mon Nov 02, 2015 4:48 pm Post subject:

Hopefully you have the point boards for the PG. Art Sonneborn had a PG stack back many years ago, so it is do-able! you may need to set the Sony up first, as it has the most limiting of the convergence controls, then converge the PGs to it.

Keep us posted! Very Happy

Rattanee · Joined: 18 Jan 2015 Posts: 193

I'm on the lookout for one or two PG point boards, as time and money permits. I read you already got rid of all your pg stuff, which makes me sad I missed out on it, but then again I had other things to spend on the past few months :\ I have one working Point board though.

I'm not really aiming for an actual stack, I just want to put my near-pristine tubeset in the center PJ, and only use that for movies and whatever doesn't risk phosphor burn Smile

The Sony's tubes are pretty much used up, swhy I want to use it for retro games... I won't be sorry for further burn Very Happy

**Curt Palme** · Posted: Mon Nov 02, 2015 5:44 pm Post subject:

What are you talking about? OF COURSE you want to try a stack! Very Happy

Even if the edge convergence is off, try it anyway to see what you think. I think you'll love it!

Rattanee · Joined: 18 Jan 2015 Posts: 193

Rattanee · Joined: 18 Jan 2015 Posts: 193

So the time has come... I have two PG6 plus (soon-to-be converted to PG9 plus) sets to be mounted on the sides, and a Barco Graphics 808s going in the middle. There's not much to say about the barco setup (except that damn it's much more simplistic then the NEC... ), however the physical installation of the PG6 plus machines begs some questions.

If I adjust the lens flapping, that will also move my projected image. I am mounting the PJs in unistrut rails with custom machined slides so that I can slide them back and forth if necesary (giving them about 80cms play), so proper mounting angle is paramount. Once I have the unistrut mounted, I will not be able to adjust the angle of the sets.

Seeing how flapping moves the center of the projected image, I am curious if there is a way to accurately calculate how much I will need to 'overshoot' the angle of the projectors so that I will get the center of my green raster right where I want it on the screen? Or is it pretty much trial and error? Would I maybe be better off if I milled some out of the tube mounting rails so that the green tube can also be moved for toe-in and just aimed the PJS straight at screen center ?

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

Be aware, SOME projectors allow lens flapping adjustments on all three. Marquees do. If I ever run a multi projector setup, it'll HAVE to be side by side. My ceiling is way too low to consider a stack. So I'd adjust one to shoot a little left, and the other to shoot a little right.

Rattanee · Joined: 18 Jan 2015 Posts: 193

So I set up everything, and I ran out of keystone... will need to add a second set of rails so I can move the things sideways too :\

What I did was tape a string to the top center of my screen, and used that to figure out the angles of the projectors... I could have moved them just a little closer together maybe, that would have helped as the angle would have been slightly smaller. As it is, I can dial in the green tube okay (maybe one or two more steps of keystone would be welcome, but some of the other adjustments go out of range, and converging the other tubes is proving a nightmare...