CurtPalme.com Home Theater Forum

[jimbrouwer]

This might sound like a stupid question, but is it possible to use 2 projectors on the same screen at the same time, with the same input to make a brighter image?

Would it be technically possible to converge the 2 projectors this way?

Would I have to hang one projector from the celling and the other beneath it on a table ?
or could i have them side by side?

Has any one had any experience of doing such a thing?

is it a thing?

I have 2 Sony g70's and the room installing in has ambient light hence the need to try and make the image brighter.

thanks

Jim

[cmjohnson]

It's called stacking, and yes, it works like that, and it's highly regarded. Stack if you can!

But the installation requirements can create a lot of work for you.

[jimbrouwer]

does anyone know of any more information / tutorials / manuals on how to do this please ?

[ecrabb]

Ambient light and CRT - even a stack - is a bad thing. You're much better off with a large direct-view set like an LCD if you have to deal with ambient light. The projectors will never compete, and your shadows will be filled with light so you never see shadow detail. You'll either want to deal with the ambient light issue somehow, or go to direct view set.

As for stacking, there are no manuals or tutorials. If you search on the forum for "stack" or "stacking", you'll find lots of information. Curt himself is running a stack with two Barco projectors. You can probably find his thread.

The basic gist is that you want to get the two projectors as close together as possible. If you go with a little larger screen - say 3m wide - your geometry will be a little easier. Critical physical setup is ideal. You set up one projector, then align the second projector to the first. It's A LOT of work.

SC

[cmjohnson]

Yeah, NO ambient light with CRT projectors.

With the projector turned off, if you can see the screen, what you see is the lowest possible BLACK level.

And if you can see, the screen, it's not BLACK!

Only a properly adjusted CRT projector can keep that black level black with the projector turned on.

But it requires no ambient light in the room.

[ecrabb]

BTW, here's Curt's thread on his stack:
https://www.curtpalme.com/forum_archived/viewtopic.php@t=36703.html

Note that the relatively large distance which separates Curt's 909's isn't typical for most stack installations. He could get away with that with his Barco 909s because they have huge geometry controls, but the G70 is much less flexible. I'd mount them so the two projectors were nearly touching corners right on the screen centerline.

If I were you, I'd do some reading on this so you have a good handle on what it entails, then I'd set two machines up on the floor and give it a whirl so you can see what you're getting yourself into.

Center the green raster on a projector, and put its front corner on the screen centerline. Swing the projector's rear-end and pivot on that corner that's on the centerline until the image is centered. Then you have to make sure the raster will fit well on the red and blue tubes, and possibly move the projector forward or back. You'll need a lot of Scheimpflug focus on all three tubes to counteract the rotated projector. Lots of iterations to get geometry and focus right. Once one is nailed down, start with the second machine and align it to the first.

Just keep in mind that with a CRT stack, you double the good thing (contrast), but you also double the bad things (drift/maintenance and noise).

It's fun, though! Try it!

SC

[cmjohnson]

Rather than stacking, you might enjoy a blend instead. You can thus get a wider picture and even if you run a fixed aspect ratio system, like a 2.35:1 aspect, you will make efficient use of your tube phosphor area as each CRT's tube faces will be mostly covered with active image area.

For best results, you want to use as much CRT face as you can. Benefits are longer tube life, less wasted phosphor area, higher resolvable resolution, more light output. To do a widescreen blend, both projectors run their tubes at close to full frame, rather than a narrow stripe of tube face for a widescreen single projector setup.

With blending you can reasonably get a screen width of up to 12 feet with a bright, punchy image, with an 8" tubed machine like a G70. Smaller screen sizes imply greater available brightness, of course.

[jimbrouwer]

the image i will be displaying is 4:3 as it will be specifically for installation/Video in a gallery
hence why I want to make it as bright as possible.

sounds like its going to be quite a time consuming, and difficult , i don't think i will be able to do it in the time frame. for something that is only going to be there for a few months. but i will thinking about it...

[Curt Palme]

Do the stack! It does take time to set up, but well worth it. I watch mine an average of 2 hours a night.

[Curt Palme]

Do the stack! It does take time to set up, but well worth it. I watch mine an average of 2 hours a night.

[cmjohnson]

For an installation like that, in a gallery, stacking has the added benefit of built-in reliability. If one projector should fail, you'll still have a picture.

However, it is fair to point out that you can pick up a cheap digital projector for peanuts these days that puts out a lot more light and is better suited for a room with some ambient light. While I'd much rather watch a movie on a G70, cheap LCD projectors might
actually be a better fit for this application, and setup is going to be pretty easy.

[xmob135lc]

Perhaps , mount the projector vertically, project onto a mirror , then onto a rear projection screen, and use black curtains or a complete fake wall. Also there are still such DLP rear sets made by the chinese, if you don't need the motion qualities of a CRT , or you can get the screen without the enclosure, in some arbitrary size from them (doubtful they make the better ones in arbitrary size because of the fresnel / lenticular "layers" , also colorshift is not out of the question with uncompensated optical layers , -they don't need such compensation with -single lens- DLP).

[garyfritz]

I agree with CJ ( ). For your application, **especially** if it's only going to be there for a few months, the headache and issues of a stack are not worth it. Get a cheap light cannon. Or, if you have the budget, get a decent projector with at least 1080p resolution. The digital will be brighter, which will go a long way towards "looking good." The setup will be trivial, the projectors won't get in the way in the gallery, and you'll have far fewer hassles.

Save the G70's for your own setup at home.

BTW how bright will this gallery be? Does it have big windows with direct sun? That will kill ANY projector.