Film-Tech Forum ARCHIVE: Projector Plinths

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Posted by David Graham Rose (Member # 1450) on 09-22-2004, 03:03 PM:

Greetings All from a highly dreary Cambridge

I have recently been on an excursion of theatres in the United Kingdom as part of my work for the Film Council. There are a number of points upon which clarification is necessary.

a) in the main, installations having Cinemeccanica projection apparatus in 78% of installations (of this type of projector) are mounted upon what one can only describe as 'plinths'.

b) installations with Century (or what was the Westrex projector) have 'plinths' - albeit cleverly designed steel frames - in only 1.3% of the installed apparatus.

Whilst during the course of my research, there are roughly equal numbers of Cinemeccanica and Century in operation here in the UK I find it necessary to question these statistics.

Could it be that Cinemeccanica projectors are ill- equipped for the design trends and porthole positions of the UK multi screen auditoria? I am led to believe not, since even the prestigious Odeon Theatre Leicester Square is furnished with what can only be described as negative 'plinths', where the highly polished parquet floor has been excavated to accomodate said plinth. Could anyone shine any light on this matter, since I need to report back to the Film Council as to the suitability of said theatres for future digital cinema installations.

On another point, do US projection apparatus manufacturers, sensibly position the optical axis to align with current standard regulations of porthole height, or has Brussels once again interfered once too often?

From a Wintery Cambridge

David

R

Posted by Ken McFall (Member # 845) on 09-22-2004, 03:31 PM:

Hi David,

the need to use a plinth is determined by the height of the porthole and the rake of the projector in relation to the height of the projector lens. Also in a few cases to clear the heads of people in the back row!

Before you start to consider if a particular projector make has a need to use a plinth by 'design' you need to include the above considerations in your findings.

The projectors have, in many cases, been installed into an existing older building and have had to fit the existing ports. In newer sites the ports will have been positioned to suit the projector. Also newer sites tend to have larger ports than older buildings so there is much more latitude.

Regards.

Posted by Paul Mayer (Member # 355) on 09-22-2004, 05:04 PM:

One of the new theatres here (built in 2001) was designed with very steep rake angles needed to light most of the screens. But the ports were installed at standard height. So most of the consoles had to be mounted on custom-made pedestals in order to achieve the rake needed and still get through the port hole. The installation techs had to fabricate the pedestals on the fly--initially they just used stacks of cut 2x4's. [Smile]

Another new construction here got the rake angles much better, but blew it on the port sizes. The booth wall was very thick--so thick that with the THX-certified front glass in place the picture was vignetted. The initial workaround was to leave the auditorium-side glass off the port and go with only the booth-side glass in place. Don't remember what the final solution was for that one.

Ah, the wonders of modern multiplex theatre architecture! [Roll Eyes]

Posted by Daryl C. W. O'Shea (Member # 1303) on 09-22-2004, 05:10 PM:

Most, if not all, first generation DLP setups are mounted on standard 35mm consoles or pedestals. So if a standard console or pedestal already fits in place, so will a DLP (or other digital type) install.

We all know the DLP folks aren't the brightest [Wink]

, but they're not dumb enough to build something that won't fit in existing theatres.

Posted by Scott Norwood (Member # 30) on 09-22-2004, 07:27 PM:

True, but there are some issues with the Barco DP100 (new 2k DLP) and steep tilt angles. I recently saw an installation which involved the aforementioned 2x4s in order to get the same tilt angle that was accomplished with normal Simplex 5-point pedestals for the film projectors.

Not sure about the other current-model DLP machines, as the only other one that I've seen up close was a first-generation model based on a Christie SLC console.

Posted by Paul Mayer (Member # 355) on 09-22-2004, 10:07 PM:

The Sanyo's I've worked with didn't have enough vertical lens shift to deal with the rake in stadium auditoriums. Always ended up having to shim the back end and deal with any resulting focus flatness issues. Anytime I go out on a video projection job these days I carry a few 2x4 blocks in my expendibles box. 2x4: a.k.a. "Coarse Vertical Centering Adjustment." [Roll Eyes]

May have a new full-time job shortly, working with some of the newest Barcos. Hopefully I will get to see firsthand what sort of tilt/shift range they have.

Posted by Ian Joseph Parfrey (Member # 2682) on 09-23-2004, 01:12 AM:

In my experience here down under, the primary reason for projector plinths are for the prevention of transmitted projector motor vibration through to the floor of the bio and hence to the auditorium. Bauer recommend plinths in their manuals for the U3 U4's. I'll bet most of the plinths you found are built out of timber for that very reason.

Cheers and Beers