Imax used to be Only Film, however, there are many films shown on imax
screens using the DLP digital projectors now. A lot of people have complained
because of this. (so Yes, they have multiple projectors)
I will also add, 3d can and Has been done in Imax without Digital projectors.
To do 3d with Film, they use 2 projectors.
One image is polorized, and so the eye with the correct polarity will only see that
side.
Most theaters only have one projector per unit. So, they were not set up for
3d movies. Imax 3d had the dual projectors, and was the first fo show full high
def 3d material. Most of it was cheezy as heck... but it was still very cool.
Also, because Imax screen is so much larger... and that the seats are much more
vertical in positioning (closer to the screen) The 3d image comes much further out
of the screen than in any other normal digital theater. Litterally, things appear
about an arms length away from you, from the very back row.
After Digital arrived... I believe they were able to use a fast switching filter to
polarize every other frame... so they would only need one projector.
Capturing 3d images is still very costly though. I believe many movies are still
shot with real film, because of the look and light reactions. 3d cameras were insanely
expensive, and used twice as much film obviously. The digital camera can drop
that cost... but then again... there is a lot more data needing storage too. Makes
special effects harder to pull of as well. (CGI that matches the correct perspectives
and depths or real live actors in 3d space) (as well as things like Fake punches,
which in 3d would be way too obvious to get away with)
So, most of the 3d stuff will remain as 100% (or close to that number) of CGI
animation. Real photographic 3d is So much better than the CGI stuff... so its very sad.
Hopefully it will change...
At least Coraline was made with stop motion and real photographic 3d. That was
really incredible in 3d.