I am a little old school when it come to this. I use the properties of a right triangle to figure this out.

/|
/ |
c / | a
/ |
/ |
/______|
b
Figure out your screen size and throw distance. Cut you screen size in half. So if your screen is 80" Wide, then make 40" the half size or b. Take your throw distance and make that a. for a we will use a Infocus sp7200 at 120".

A squared + B squared = c squared
40 squared + 120 squared = 8000
take the sqaure root of 8000 and this is the distance from the edge of the screens both left and right sides. We then take two pieces of string and make them the correct length. then I have one guy hold one side, another guy hold the other, then I take the other side of both wires to figure out where we nee to go. This was about the only way to do it 12 years ago. Now everone uses lasers and laser plum bobs. We still do it the old fashoned way.

Mike

This method requires that the two strings are exactly level as well, right? Do you use some sort of hanging level to confirm that?

So this gets you just below the centerpoint of the ideal lens location - do you use a plumb bob to then figure the location at the ceiling?

The Kloss Novabeam actually came with the string to do that with...

Now I'm dating myself...

Thank you all for the helpful info and insights - we got the projector set up last week, and although there were a couple of tense moments, the install went quite well and the projector ended up being within 1/8" of center of the screen ... w00t!

Alas, my idea of using my high-falluting PLS2 laser to first plumb out the vertical center of the screen wall and then follow the orthogonal arrow back along the ceiling to find dead-center for the projector mount kinda ... er, didn't work. I neglected to account for the fact that this would _only_ work if I had the PLS2 laser line dead-perpendicular to the projection wall, and there was no way I could figure to do that.

However, using the old-fashioned method of measuring off the side-wall worked (and double-checking against the other wall) ... lucky, now that I think back on it, that the side wall(s) were not too far out of perpendicular with the projection wall!

The laser plumb _did_ help a bit when "squaring" the projector lens with the projection wall, though ... by projecting a test pattern and ensuring both vertical sides of the image were plumb.

Anyhoo, overall it was a grand success and the client's ecstatic ... the only issue was I couldn't completely dial out the "yaw" of the projector with the Omni mount I was using, so the picture remains tilted approx 1/2-degree w/respect to the frame; however, it's only noticeable with test patterns.

Incidentally, the picture looks fan-bloody-tastic with the Sony Ruby and the Screen Innovations 1.1 gain we picked ... and we've not yet done even any basic calibration of the set!

LOL!!!!!!!! Oh my god! That jogs the memory a bit! I forgot how long front projection has been out there! I remember the curved screens. Looked pretty bad sitting there in the ol' living room! We always had a Novabeam set up in the dark corner of the store, and whoever came in with the worst hangover that morning, would lie on the couch watching Road Warriar (on Lazerdisc), for an hour or two before hitting the sales floor... This one guy, Wayne would sometimes fall asleep on it for hours.
My buddy had the NovaBeam with the coffee table cabinet... we all thought he was about as cool as Hugh Hefner for being able to own one of those!!!

I had one of those - A model One-A -- and loved it. That was the "coffee table" model.

We had it for 20 years.

I was fortunate on two accounts -- one, the Kloss engineers were here in the Boston area and could fix it and I had two repairs on it at very reasonable cost - and on the second repair, I had a full re-alignment done and the picture was better -- 12 years after I took the set home for the first time -- than it was when I first bought it.

The other -- I had the room for it, a 18 x 22 foot playroom.

It was still working fine -- it had a twitching problem, but that was a user repair.

But it was time to go "high definition" -- and it was also time to reclaim our playroom and so I practically cried when I took it out -- and I gave it to a repair shop that specialized in high end video (Elite Video) -- and that saved me the cost of disposal.

I had tried to sell it on E-bay -- with conditions -- you gotta pick it up at the house, I'll help you move it, etc. etc. and I had a $20 reserve on it but got no bids.

I don't miss it now.

20 YEARS??? I'd say you got your money's worth. Pretty cool when something holds in there that long ang gives you a zillion hours of enjoyment! That's the part of the Biz I like.

I think the bad ones, do, too. But are they correct?

With regard to the numbers in manuals: I installed one of the first Sony G90s in the country, and it is a "good projector." I investigated the numbers in the manual because I needed to be DAMN SURE that the box we built down from the ceiling was in the right place. Turns out that they listed the throw distance in the manual as being from the lens to the screen. In reality the number they gave was from the center of the mount to the screen, which was about 13" further back. In other words, if you follow the above advice, you will be able to do an install as good as the manual. I always get the projector out and throw an image on the screen to be sure that the numbers in the manual are correct. THEN I follow the numbers or modify them if needed.


It is not always possible to place the projector at the right height. The client might not allow it. But as txvisser and others discussed above, left and right only requires a piece of string. You should NEVER have to use horizontal keystone. You only have to master using a piece of string!


How about the manuals that tell you the distance from the lens to the center of the screen: STUPID BEYOND BELIEF ! ! ! I'm, what, supposed to nail one end of the tape measure to the center of the screen (which is hanging loose), then take the other end of the tape and scrape it on the lens, moving a 30 to 50 pound projector AND ITS MOUNT until everything is in the right place? Talk about a Microsoft answer (technically correct but totally useless)(as in "you can bla bla bla" but not telling you HOW you can).


What is the advantage of this? If the screen is a particular size, the zoom on the projector allows you a range of positions where you can mount the projector. I have heard people worried about brightness, but if the image is a particular size, different throw lengths via zoom will only affect brightness if the smoke in the room is so thick that the opposite side of the room is hard to see.

Not only that, I had to mount a JVC in a room at its absolute maximum length (I can never remember if that is maximum zoom or minimum zoom), and all was okay. Then we upgraded to the same chassis with a brighter bulb, and guess what: the image could not be made small enough to fit the screen. There was just the slightest variation in optics from one unit to the other…so NEVER use the absolute end of the zoom range!



This sounds good, but please tell us the technical reasons for this. Exclude a smoky room as a possible scenario. As mentioned by others above, if you put the projector as far back as possible, the image only goes through the best part of the lens. That is, the image will be small all the way through the optics, and the less width of lens that is used, the less opportunity there will be for any tiny lens imperfection to affect the picture. I started a second ago thinking you should give me a reason why you put it as close as possible, but now I think you just plain have it backwards.


This is a matter of being on top of the electrician and making sure he doesn’t do anything until you tell him where to do it. As you say, experience. And you really should have all this down by about projector fifty-seven.

By using the zoom, you actually loose light on the screen. The effective f stop, like on a camera changes as you zoom the lens out. On the other hand having it set up for the min distance gets you a little distortion on the edges. Best to just use a little zoom for a sharper picture.

Has anybody pointed out that the string you use shouldn't stretch?

WHY and HOW is light lost on the screen by using the zoom?


As I said above, I can never remember whether zoom in is a small picture or a big picture. What I'm getting from what you say is that putting the projector as close as possible is using minimum zoom, right?

But wait -- if you put the projector at the maximum distance, then the image will be smaller as it goes through at least some of the lenses. The central areas are less likely to have any optical aberrations, so the image is likely to be more clear.

Another thing, closing down the iris on a camera gives you better depth of field because less of the lens is used and there is more of a pinhole effect; I just don't know if this translates to projection.

Duh. I assumed the keystoning was the way to compensate for pj vs. screen height. I've only done a few pj's in the several years and have measured height dead on so far, but have several coming up where height might be a problem. I didn't realize keystoning affected the picture so adversely.

How far can you adjust height on the pjs before the keystoning messes things up?

I have a Sony VPL-VW100 going up this week with a Draper Premier 106" with about a 17' distance. I called Sony to see if I could mount the pj 6" above their diagram but they had no clue.

Any thoughts?

Not sure if this helps you, Steve, but I found that vertical lens shift on the Sony covered a great deal of range .... didn't measure it, but it *seemed* like it was more than the manual spec'd.

every projector has a projector offset.... that means difference in projector height to screen height....

using keystone adjustments mean you most likely did not hang the projector properly....