TWINING BARCO 20c PROJECTORS

[Allan Barnes]

Has anyone here "twined" two Barco projectors (to increase brightness) with an external Dolby server. I believe this was "popular" in the early days of digital 3D films. LOOKING FOR ADVICE and PITFALLS. Yes.... we have avoided the PROJECTOR IP CONFLICT on our local network and we are using the same sized LAMPS and LENS. We are awaiting a BNC SPLITTER to jump the A and B signals to between projectors. CALL IT A TEST or SCRATCHING AN INCH..... this just might work.

BACKGROUND... we don't have 3 phase power and my Barco 23B restoration project has stalled due to a dead light engine and no new/used part replacement.

[Steve Guttag]

I'd switch your title name to "Stacking" as that is the more common phrase. Barco used to have (and may still have) stacking cups to put the upper projector on top of the lower one. They also had a rear cover that allowed the bottom projector to vent out of the rear (since the upper projector would block the exhaust up there).

[Ryan Gallagher]

Yeah "Stacking" is the industry term for it. It's cousin is "Blending" (for doing very large screens). (and "Mapping", for when the screen/surface is not a rectangle).

In the ALT content and non-DCI space it is as simple as having them both on with the same signal and making the adjustments necessary to get the image as close as possible converged. Manufacturers even have software to mostly automate some of that process, ideally you do it entirely mechanically (not always possible), but it can also be done via software or the geometry engines sacrificing a little bit of pixel perfectness.

In the DCI space it is a little more complicated, might require two media servers that are frame sync'd (and a stacking license), each brand had a specific way of implementing it. Less common now but still supported afaik. Exhaust routing is definitely an issue in a DCI Xenon stack. Probably extra steps for getting correct gamma and color too.

(Have done it plenty with non DCI projectors, never done it for DCI myself).

[Marco Giustini]

I believe this was "popular" in the early days of digital 3D films

in 3D, the image alignment is not critical as each projector will reach a different eye.
If you want to do staking in 2D, mechanical alignment is going to be critical and not simple. You won't be able to use the lens zoom once everything is aligned (lenses are not so accurate and you'd lose the alignment if you switch between, say, flat and scope) and you'll have to re-align your image daily.

Also, If you need to access the bottom projector, you'll have to remove the top one (though you can also install the projectors side by side but I think that you'd end up with more distance between the lenses = worse overlay between the two images)


If it's for fun, go ahead. If it's for a commercial installation, bear in mind it's going to be a Royal PITA!

[Jim Cassedy]

Stacked Thoughts:

Until earlier January this year, the venue I'm at had a stacked pair of SONY SRX-515B
projectors in our largest auditorium, which ran off of a single SONY XCT-M10 server.
Each projector had an extra interface card and software installed to enable the dual
operation, and there was a thick (almost 1") armored cable running between projectors
to sync them. The cable was protected by DCI security , so if it was unplugged
or tampered with, it would trigger a tamper alarm which had to be re-set.

Our reason for doing dual was to get extra light on our big screen. There was an
'auto-alignment' program which used a small camera mounted in the bottom of
one of the projection ports that we would run to tweak the image alignment on
screen. It took about 10min, and I'd usually try to do it early in the morning or after
the last show, when there was nobody in the auditorium because it worked best when
ALL the lights in the booth and auditorium were out. (for example the aisle runners
and seat number lights, which I could kill by flipping a circuit breaker) The big
advantage of dual projection was when running 3D, since the 'left' & 'right' image
each had it's own dedicated projector. Dual projector 3D, either digital or film, is
really the best way to do 3D if you want to do it at all.

Over at Dolby's Market St screening room, they used a pair of custom modified Christie
laser projectors. Their set up was side-by-side, but they too had a special auto alignment
program that we were required to run every day. Their alignment program took about 30
minutes to complete, and also required as close to total darkness in the booth and
auditorium as could be realistically achieved. Dolby's set up used two IMB/servers,
which were synced by cables & software, but the projectors were configured as
"master" & "slave", so you only had to load content once.

A "stacking" arrangement is a bit better than side-by-side, just in terms of dealing with
alignment, and it takes up less floor space too. But as someone else mentioned, the
issue you might run into is projector exhaust ducting. The SONY's had their 8" exhaust
ports at the rear of the projector, so the stand they were on had the projectors displaced
horizontally by about 1 foot, so that you could easily run a flex-duct down to each one.
(so the top projector was about 1ft closer to the projection port than the bottom one)

At the historic Grand Lake Theater in Oakland, they have a pair of stacked Christies
to get good light in their largest auditorium, which has a huge screen and a very long
projection throw. Christie makes some sort of adapter that moves the lamp exhaust
from the top of the projector to the side, which is how they vent the bottom projector.

[Marcel Birgelen]

Barco doesn't offer a DCI compliant stacking solution for those projectors, so 2D alignment is going to be next to impossible to achieve and maintain.

Christie offers a stacking solution with and without mirrors called Christie Duo, which also works with their older projector lineup, I'm not sure if they're still selling new installs. Newer Christie projectors support Mystique, which requires extra licensing, but which allows for automated camera-adjusted stacking and edge-blending, even with a select number of DCI projectors.

[Steve Guttag]

The rear exhaust is still listed. Part R9801016. The stacking points (cups) R9801017 are listed as "End of Service" which means they are no longer made/sold.

[Marcel Birgelen]

For 3D only solutions, I'd go for a side-by-side setup instead of a "stacked" solution, unless it doesn't fit in the booth otherwise. I've only ever seen early DP2000 setups as "3D stack". Like Marco noted, in this setup, accessibility to the bottom projector is going to be extremely limited.

There are still some advantages for a dual projector setup in 2D, obviously: You can share the load between machines and you have a potential backup in case of an unexpected failure of one of the two units.

[Allan Barnes]

Thank you. All helpful advice