CurtPalme.com Home Theater Forum

lyd · Joined: 15 Sep 2007 Posts: 390 Location: Lake Mills, Wi

Well, a year has passed in the new location and my projector, speakers and amps are still an inert pile in the middle of my living room floor. Yes, I am single. Also working too damn much. *sigh*

Anyway, I just came across an interesting concept that I had not seen here in all my searching during my first setup, and thought I would stop by to post about it.

I need to copy some artwork and was trying to figure out how to square a camera to a wall, not trusting the usual measuring-the-diagonal way in this situation.

What I learned about was a method involving two mirrors, one circular and with a hole drilled through the exact center. The idea is that you look through the hole from the backside of the one mirror, point it at the other mirror, and when all the repeating circles are concentric off to infinity, bang, you are square to a very high degree of precision. In most implementations the mirror with the hole is mounted to a short cylinder, with another small mirror at a 45 degree angle inside, so you can see through the hole from the side.

It occurred to me that a version of this might work well for squaring the projector rotation to the screen, after you have established your centerline using the usual methods.

I thought that you might be able to suspend the mirror with the hole in it from the projector, using two lines so it was hanging plumb and square to the front of the projector, and then attach (or have a helper hold) the other mirror against the the screen. Then you just look through the hole and adjust your pj rotation until the circles are concentric to infinity. No need for the 45-degree assembly here. You don't even need a circular mirror, just drill a hole through a square mirror, then draw a perfectly concentric circle around that hole.

Lot of finicky mucking about, but no more so than a lot of alignment methods. I think it could be extended to align in all ways, with some more setup. You could put a mirror with a small hole in it over the green lens and throw up a solid pattern. Then place a flat mirror shimmed up off the screen to the exact angle you have calculated you need, in the center of the screen and with a small mark at the precise center. Just trim it all up until you only see a single perfect circle of light hitting dead center on your marked point. All degrees of alignment perfect, in one fell swoop. Assuming the front of the green lens barrel is square to the front element of the lens, anyway.

*shrug* There you have it, FWIW, YMMV, MOUSE.

lyd

**AnalogRocks** · Posted: Tue Jun 02, 2009 5:04 am Post subject:

Not to bust your bubble ( or break your mirror ) but isn't it just easier to measure the distance from the red lens to the screen then the distance from the blue lens to the screen and make sure they are the same?

Gino · Posted: Tue Jun 02, 2009 5:23 am Post subject:

AR - that method has faults. What if your projector was slightly rotated, but slightly off centre in the direction of the rotation? You could still measure equal distances.

ecrabb · Posted: Tue Jun 02, 2009 6:18 am Post subject:

Gino's right. You can't just check the two lenses for the reason he stated. You'd have to also measure to the back corners of the chassis to catch the rotation.

The mirrors thing... One with a hole, attaching it plumb and square, looking through the hole, and hoping you don't have any error anywhere... Sounds like a lot of dicking around with a lot of potential for error.

I still say the spinning laser is the easiest if you have one. If you set it up right, it strikes a line through screen center, across the ceiling, through the center of the green tube, and right down the center-line of the projector chassis. Bada bing! Takes about 15 minutes to set up right, and it's extremely accurate.

SC

jask · Joined: 17 Mar 2006 Posts: 10187 Location: kamloops BC

Tom.W · Joined: 09 Mar 2006 Posts: 6635

Quote:

I still say the spinning laser is the easiest if you have one. If you set it up right, it strikes a line through screen center, across the ceiling, through the center of the green tube, and right down the center-line of the projector chassis. Bada bing! Takes about 15 minutes to set up right, and it's extremely accurate.

Can you elaborate on what method you use to align the spinning laser to the projection path of the projector ?

garyfritz · Joined: 08 Apr 2006 Posts: 12088 Location: Fort Collins, CO

My preferred method for squaring the projector: http://www.curtpalme.com/forum/viewtopic.php?p=79360&highlight=measure#79360

I tape "distance from screenwall" measures on the side walls so I can easily sight along the projector and instantly tell if the pj is square or not. Works a treat.

ecrabb · Posted: Tue Jun 02, 2009 3:30 pm Post subject: