Film-Tech Forum ARCHIVE: How far off center can a digital projector be?

This is topic How far off center can a digital projector be? in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=000355

Posted by James Waite (Member # 4536) on 04-21-2009, 08:31 PM:

I've heard a digital projector can be further off center of the screen than a 35mm. Partly due to a keystone adjustment and I was told special lenses?

One of the biggest problems in my theatre is we have a projection booth that's just at the back of the room under the balcony. When people stand up they can block the image. It was built as a multipurpose room. I've got a upper lighting booth that isn't big enough for a 35mm setup but would fit a D-Cinema setup since there's no platter. However it would be shooting downward at a pretty steep angle, about 45 degrees. Another reason it can't be used for 35mm.

Does anyone know if I could reasonably put a digital projector up there and still have a good picture?!

There's a short video of the theatre on my facebook page for Western Film in London Canada.

The lighting booth is at the very top of the room. The current booth is under the balcony and not visible in the video.

Thanks in advance for any replies.

Posted by Demetris Thoupis (Member # 833) on 04-22-2009, 02:15 AM:

45 degrees is not steep enough comparing to what they have at Odeon Leicester square in England! Odeon Leicester square is so steep that even the keystone adjustment was not enough to straighten it. I think it was more than 45 degrees.
Demetris

Posted by Stephen Furley (Member # 1277) on 04-22-2009, 07:46 AM:

The Odeon is nothing like 45 degrees, though it is quite steep. Here's a picture from Hugh McCullough's site when it had the Vic X machines:

web page

It's probably about 25 degrees.

I did see a picture of another theatre recently which really was about 45 degrees, but I can't remember where it was, or where I saw it.

I haven't seen any posts from Hugh here recently; I hope he's ok.

Found it, it's in a video clip linked to by Leo Enticknap, who I also haven't heard from recently. It's in his second post on page six of the 'Women relly projectionist?' thread, in the Film Handler's forum.

Posted by James Waite (Member # 4536) on 04-22-2009, 09:38 PM:

I was at the Odeon last year to see Iron Man playing in Digital, there was a definite curve to the image caused by the extreme downward tilt. It wasn't too bad in the image but was very visible in the credits. The credits were curved like a smile.

Posted by Stephen Furley (Member # 1277) on 04-23-2009, 01:49 AM:

Yes, it is noticeable at the Odeon, but the rake is much less than 45 degrees. As to the original question, the only digital projector I have experience of is the NEC NC800C. On that model the lens can be moved, similar to the front shifts on a large format camera, I know it can be shifted horizontally, because this had to be done at Croydon, but I'm pretty sure it can be done vertically as well. However, there are limits to how far this can be done, and I am pretty sure that it would not be possible to obtain satisfactory results in the situation described. This would involve a much bigger shift than was possible at Croydon.

Posted by Demetris Thoupis (Member # 833) on 04-23-2009, 06:52 AM:

I think this Leicester Square Drawing is a better indication of Leicester Square!

Posted by Stephen Furley (Member # 1277) on 04-23-2009, 10:03 AM:

Demetris,

If that drawing is accurate, and I think it's fairly close, then the rake is a lot less than 45 degrees, though it's still far more than is desirable. I haven't been there for a while, but the last time I saw a film there I think the screen frame was tilted backwards slightly to partially compensate for this.

There are plenty of cinemas which were far worse than this; the Astoria Finsbury Park for example was pretty extreme. Strangely, at another Astoria, the Brixton one, which is now a music venue, the projection box was permitted to be installed under the circle, and gave an almost level throw.

Interesting that it says the original screen was made of metal; I've never seen that before.

Posted by Demetris Thoupis (Member # 833) on 04-23-2009, 10:25 AM:

I've been there last summer. I wanted to watch Dark Knight there but instead I watch Mummy 3 or something! It was a Digital Presentation and I believe the projector they now have is a Barco. I don't recall the screen being tilted but I do remember that even on the Digital projector they could not fix the keystone on the image so I do recon that the angle must be great. Did you know that this specific odeon was one of the first to carry Digital Projection from the original TI projectors. Back then they showed Tarzan in 1999 and also played back the 35mm for backup in case the digital projection got screwed!
Demetris

Posted by Mark Gulbrandsen (Member # 72) on 04-23-2009, 04:37 PM:

A beautiful theater it is but I suppose in the British "stiff upper lip tradition" [Confused]

it still has to be located in the "Box" [Roll Eyes]

. Perhaps because of some union nonsense [bs]

or something, perhaps because the management wants to keep the operators sweating [puke]

. This is one serious case of poor design and D-Cinema gives a theater with a major problem like this a great opportunity to set things straight... [fu]

literally! I certainly would have placed "14" down at about "25" had I designed that theater!!! Even in this day and age of low attendance forgoing a few seats and enclose the D-Cinema projector in it's own little hut(Yes, they are that reliable!). Kinda like how the Omnimax lens pops up in the middle of the seating areas. Seriously, you need to consult with [steve]

to get a proper design!!!

3-D polarized would suck at this theater(Or do you call it a Kinema? Dinema might be better today!) Dolby 3-D would probably work ok though...

Also, [Eek!]

position 55 and 31 should be reversed for better spatial spread... but thats a debate for another forum(someplace else for sure).

The Chicago Theater has similar problems but not as bad and at least position 55 has been split between the seating area. I won't discuss the water fall console lift they have there that is very distracting during quiet passages.

Mark

Posted by Stephen Furley (Member # 1277) on 04-24-2009, 03:04 AM:

All this is nothing new of course, and many theatres had to have new projection rooms constructed at a lower level when Todd-AO came in.

When the Odeon was built, I think it opened in 1937, you often didn't have any choice as to where you put the projection room, as the egulations often wouldn't allow it to be anywhere else. I'm told that the original design submitted for the Astoria, Finsbury Park included a projection room at a lower level, as at Brixton, but this was rejected. Why this was allowed in one location, but not at the other, I don't know.

The Odeon has undergone two fairly major refurbishment/modernisation projects in its fairly short life, but the projection room remains in its original location. It's very large, it has to be to fit in the amount of equipment it has, and I think it would be difficult to find room to re-locate it elsewhere. The last time I saw it there were three dual-gauge film projectors, two digital projectors, plus a third not in use, two followspots, a small video projector, used for subtitling I think, plus sound equipment etc. However, it might be possible to put a digital projector lower down. I don't know if the 'BBC Commentator's box' still exists, but that might be a possibility, or somewhere under the circle. Acess to it wouldn't be needed during a show; it could be operated remotely, and the servers etc. could remain in the projection room. How much of a digital projectorhas to be in the projection position position? Is there a case for making a projector split into two parts, with a projection head made as small as possible, and everything else, power supplies, cooling etc. located remotely? Isn't this similar to what Imax does with film projectors?

Posted by David Graham Rose (Member # 1450) on 05-02-2009, 06:34 AM:

Greetings All

The Odeon Leicester Square has a rake of 18 degrees.

Regards

David