Film-Tech Forum ARCHIVE: Projector Placement along centerline in tight booth

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Posted by Barry Floyd (Member # 385) on 10-22-2012, 01:28 PM:

As our season winds down at the drive-in, it's our intention to make the switch to digital during our "off-season" from December thru February. One of the things I'm going to have to do at our place is enlarge the concrete pedestals on which the projection base sits on. Currently in both booths, my existing projectors are sitting on 24" wide x 48" long x 20" high concrete pedestals which are required to get the projection beam high enough to clear the roofs of the SUV's and trucks on the back rows closest to the building. Our building is a ground level one story concrete block building with a gabled roof. Adding a second story is not an option.

One of my booths isn't going to be an issue as there is plenty of working room available on both sides of the new projectors. However, on Screen 1, the existing concrete pedestal is placed directly on the center-line of the screen, with 25 inches clear between the exterior wall of the booth and the side of the concrete pedestal.

The new Barco DP2K-23B is roughly 29 1/2 inches wide, but the lens is off-set approximately 8 5/8" from the left side of the projector. If I off-set the projector where the centerline of the lens lines up with the existing centerline of the screen, it'll leave me with about 13 inches between the side of the projector and the existing outside wall of the booth.

Will there be enough room in there for maintenance to service the projector? I haven't met a 13 inch wide tech yet?

Can the whole projector be shifted roughly 12 inches to the left of centerline and not distort the image on the screen? Is there image-shift software in the projector to compensate for the mis-alignment?

Posted by James Westbrook (Member # 3690) on 10-22-2012, 02:16 PM:

Is the 13 inch clearance on what I call the "operating" side of the projector? If so, the space will not allow for the removal of the lamp house for bulb change.
If it's the "non-operating" side, one only needs enough clearance to get the cover off to get the two filters out for cleaning.

Posted by Barry Floyd (Member # 385) on 10-22-2012, 02:46 PM:

Yep.. it's the "operator side". Looking at the rear of the projector (towards the screen), the 13 inch space would be on the right. There is a photo of this booth in the Film-Tech Picture Warehouse. Scroll down to the "Drive-In" section, and click on "Stardust". It's the photo of "Screen 1 Projection Booth".

Posted by Carsten Kurz (Member # 5396) on 10-22-2012, 03:48 PM:

Barry - in order to be sure about your potential issue - you know what 'lens-shift' means on a digital projector?

Is shifting/enlarging the porthole and base an option?

- Carsten

Posted by Victor Liorentas (Member # 5272) on 10-22-2012, 03:50 PM:

You will have very flexible lens shift capability to offset keystone or off center issues with your Barco.

That's if your tech uses it correctly. I have seen some installs that are only a little of the center line and yet keystone is more obvious than with 35mm! Mind you this was on curved screens which can amplify the problem.

Posted by Barry Floyd (Member # 385) on 10-22-2012, 04:41 PM:

I'm going to have to enlarge the width of the concrete bases to accommodate the footprint of the new digital pedestals. Right now they are 24 inches wide, but the new bases are 31 inches wide. Length-wise I think I'm OK with the 48 inch length - since the new pedestals are 42 inches long.

Our 12" x 12" portholes will be enlarged to 16x24. One of the things I'm doing now is trying to calculate exactly "where" we're going to have to saw-cut the exterior block wall to install the new projection ports. Since the new port is essentially twice as wide as the existing port, I had planned on it too straddling the centerline of the screen. I've got from now until January to get this figured out.

I've heard of the term "lens shift", but have no idea exactly what it does.

Posted by Scott Norwood (Member # 30) on 10-22-2012, 05:33 PM:

quote: Barry Floyd
I've heard of the term "lens shift", but have no idea exactly what it does.

Do you have any experience with large-format still photography?

If you want to take a picture of a tall building with a typical small-format camera, you would tilt the camera vertically to get the building in the frame. This would result in a photograph that is geometrically incorrect (vertical lines will converge toward the top of the photograph, rather than appearing truly vertical).

With a 4x5" or 8x10" or other large-format camera (and some smaller-format cameras), it is possible to move the lens with respect to the film plane. To photograph a building in a geometrically correct way, you would set up the camera with the film plane parallel to the building and then shift the lens vertically (keeping it parallel to the film plane) to compose the picture. Done correctly, this will result in a photograph without geometric distortion. You can find examples of this in almost any architecture book or magazine.

With projection, you do the same thing in reverse: set the projector so that it is perfectly level and aligned so that it is parallel to the screen. Then, shift the lens horizontally and vertically to center the picture on the screen (the picture moves when you shift the lens). As long as the projector remains level with respect to the ground and parallel with respect to the screen, you will get a picture that is free of keystone distortion. If you shift the lens as far as it can go and still can't make the picture hit the screen, you may have to adjust horizontal or vertical tilt, but this will still result in less keystoning than if you left the lens centered and then shifted the entire machine.

In any case, I can't believe that 12" would make much of a difference in the case of a drive-in, with a huge throw distance (and thus small angle difference). A two-machine 35mm booth would put the machines farther apart than that, with no obvious ill effects in most theatres.

Posted by Dave Macaulay (Member # 813) on 10-22-2012, 07:22 PM:

The problem is room to get the lamphouse out. I haven't measured a 23B but a 12C needs about 20" minimum and the 23B lamphouse is deeper. You absolutely need enough room on the right of the projector to get that lamphouse out. You also need to get at the circuit boards occasionally but they are shorter than the lamphouse. You will have to relocate the port so you have this room, maybe the pedestal support will have to be widened as well. The projector's lens point is higher than a 35mm machine so make sure the port is high enough, as I recall the minimum height above floor with the standard pedestal is around 49-50 inches - but if that'stoo low the base can jack up about 4" and the projector can jack up quite far: maybe 9 inches on a B unit.
You won't have any problem with lens shift, that's easy and will accommodate pretty much any installation. You may want to angle the projector up a bit. Note the B projector can be mounted with the standard pedestal reversed to get up angles although the lens point will move up as you do so.
Using lens shift alone with a level projector keeps the screen image geometry rectilinear but you mustn't have the lens shift set at its maximum - you'll get an error and amber tail light every time you select a projector macro if it hits the limit. So tilt the projector so the shift is not at or close to the limit. Note that when a lens file is activated the lens motors will make their final moves in the same direction as when you did it before you saved the lens file, so if it's close to the limit make sure your last move is toward the limit. If it's away from the limit the motor has to drive past the set point and come back: if it hits a limit then you get an error and the lens position, focus, or zoom won't be exactly what you set.

Posted by Louis Bornwasser (Member # 3063) on 10-22-2012, 09:34 PM:

You will not have a problem with side ways keystone since a drive in has (typically) a throw of several hundred feet. Even 10 feet off center is not a problem.

Digital usually has software to compensate anyway.

A bigger proble is the "30" clearance" required by the National electrical code; Law in public buildings that charge admission. louis

Posted by Carsten Kurz (Member # 5396) on 10-23-2012, 02:14 AM:

Yep. Forget about the centerline. Only commit to the required clearance space on the right side of the Barco and reseat/enlarge the porthole and base as required. Get in touch with your integrator and find out about his pedestal and what porthole-height you need to accomplish above your concrete base.

- Carsten

Posted by Louis Bornwasser (Member # 3063) on 10-23-2012, 08:43 AM:

Better still: order a base that is the right height and get rid of the crete. Louis