CurtPalme.com Home Theater Forum

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

After doing some reading I think the pincushion problems that I am having at the top and bottom of my screen, is gullwing distortion?

What happens is the corners either wing up or down, and I can not get the geometry accurate there.

Is there anyway to reduce or eliminate this problem?

Thanks.

ecrabb · Posted: Fri Jan 04, 2008 4:23 pm Post subject:

I don't think so. Gull-wing usually happens with a curved screen and would make convergence difficult at the 1/4 and 3/4 points on the screen. Gull-wing geometry adjustment basically splits the screen in half and sort of gives you a "bow" control for each half of the screen. So, you're really warping (bowing) the geometry at the 1/4 and 3/4 points of the screen - not the edges or center. So, I doubt that's your corner issue.

A couple of things that can give you problems in the corners... Are you certain your physical setup is spot-on? I mean down to 1/8" - perfectly centered and perfectly perpendicular to the screen. Is your screen perfectly flat? Most importantly, have you maximized rasters such that at least two of your corners are very close to the edge of the tube? If so, that will make corner convergence/geometry much more difficult.

How do just the green corners look?

SC

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

The Mechanical setup is dead on, and everything is plumb and level. It is only the top and bottom 2 horizontal lines that are showing the distortion. The line comes level from the center and then as it reaches the corner of the screen it dips up at the top and down at the bottom. If you increase the pin control you can raise the corner so it is even with the center, but then the line between center and corner is bowed.

It happens with all three tubes, and they all converge perfectly, but with distortion. The rasters are maxed, but I don't know the spacing that I left between the edge of the tube and video area. But I have tried to shrink the image in the tube face, but the same thing happens, until it gets really small.

If I shrink the image vertically, like make a 2.35 image on my screen There are no problems.

So I don't know if the lens are bad, or what the problem is, but I really think that it is optical.

My screen is 78" Wide @ 102" Throw.

Thanks

ecrabb · Posted: Fri Jan 04, 2008 5:08 pm Post subject:

Hmm... OK. Sounds like your bases are covered, then. Maybe one of the G70 guys will chime in with something helpful.

SC

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Ok, thanks. I will try and get some pictures if I can.

It is strange, and I don't think it is a basic problem. Really I can live with it, because it is not noticeable during movies, but it is on my windows desktop, and in my mind it is there so I am always bothered by it, no one else has ever noticed it.

ecrabb · Posted: Fri Jan 04, 2008 5:21 pm Post subject:

Pics would be great. Oh, and I assume you've already done a full reset (or reset everything to neutral), blown out all zone, and started over from scratch, right?

SC

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Yes everything was reset.

Thanks

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Ok I removed the green lens, and maybe I maxed the rasters out a little much 1.5mm space to tube edge. This may explain the distorition in the corners.

Major problem is I cannont move the projector away from the screen anymore. PJCalc gives the mounting distance at 105" for my screen size, and I was under the assumption that you should be closer than it says. Also I shrunk the green raster to give me around 7mm space, and measured the image from the blue tube on the screen and it is 70", I read somewhere that the is the recommended space for a G70. If I use 70" in PJ Calc the works out to be a distance of 94".

I don't know if these calculations are comparable to anyone elses setup with a G70 or not.

Thanks

AFryia · Posted: Sat Jan 05, 2008 2:05 am Post subject:

Is the distortion in the corners of the 4:3 test patterns?

If so I just ignore it.

Most of my material is wide screen and the active picture never uses that part of the raster. My 4:3 material is bound by the height of my 16:9 screen.

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

No it is apparent in 16x9.

AFryia · Posted: Sat Jan 05, 2008 6:01 pm Post subject:

When you perform the initial registration and setup with the internal oscillator P2 are you setting up at the 4:3 aspect ratio. Or are you adjusting the vertical size to fit a 16:9 screen?

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Not sure what you mean?

AFryia · Posted: Sun Jan 06, 2008 4:28 pm Post subject:

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Ok, I follow what your saying. I will give it a try this week, as I have to do a fresh calibration anyway for my new scaler. When you say stock lenses, is there a better lens option for the G70, to replace what I have.

Thanks for the help

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

I have never heard of a lens swap for the G70 to a more common lens like the HD10 series on other LC's ( like the Marquee). I do remember something about a G70VR version which had special lenses on it that are as rare as hen's teeth but I don't recall the details. I think overclocker had one so you migth search the AVS archives for his old post on that?
AFA the gullwing distorion, don't think that is abnormal either when you run the G70 with rasters as large as yours. If you look at the back of the G70 lens, it's a really wierd design that isn't a constant convex curve. IT actually has a flat area in the center which transitions to a curve on the outside. I don't know this for sure, but this feature might make the factory throw formula non-negotiable?

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

The distortion is still there with a 4:3 test pattern, same as with 16:9. The corners dip down, but it must be optical, so there is not much I can do. When I shrink the raster to give me around 7mm of space, I can adjust the PIN and get everything perfect, but the screen would be far to small.

Thanks

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON

Or maybe someone has a recommendation for a 8" CRT that would have a shorter throw distance than the G70, that I could change to. I know I could go digital....but that would be a last resort!

Possibly a Zenith 1200 would even allow a larger screen size, by the looks of the specs.

AFryia · Posted: Tue Jan 08, 2008 12:23 am Post subject:

Mark_A_W · Posted: Tue Jan 08, 2008 1:16 am Post subject:

I think your geometry is good enough.

I'm pretty sure G70's are known to gullwing - so do XG's.

I'd leave it be, geometry is pretty unimportant.

There are HD-134 lenses, but they have the same throw I think. You cannot use HD-10 lenses as they are really 9" lenses, the Marquee 8500LC just jams 8" tubes in a 9" housing basically.

Bruce uses a throw ratio of 1.22x width I think - you definitely do want to bring a G70 forward from PJCalc.

fireanimal · Joined: 17 Jul 2007 Posts: 231 Location: Stayner, ON