Film-Tech Forum ARCHIVE: Extreme keystoning

This is topic Extreme keystoning in forum Film Handlers' 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=1;t=006417

Posted by Ken Lackner (Member # 1002) on 07-30-2004, 11:51 PM:

I have seen two movies in two seperate auditoriums in the last month or so at a local 20 plex, and both times the keystoning was horrible. This is a stadium seating facility. At most stadium theaters I've been to, the screen is pretty high off the ground. These screens were only a few feet (I'd say four) off the ground, and there was a lot of room between the top of the screen and the ceiling. That, combined with the fact that the port hole was only a few feet below the ceiling (I've seen them a lot lower at other theaters) made the keystoning so bad that the credits were actually curved.

I don't understand why someone would design a theater to have such an extreme projector tilt. Isn't there some SMPTE recommended practice on the projection angle? I wonder if that was taken into account when designing this theater.

Posted by Mike Perju (Member # 1482) on 07-31-2004, 12:17 AM:

They most likely weren't thinking what they were designing... as usual. This is not unusual in "modern" multiplexes.

Posted by Bobby Henderson (Member # 840) on 07-31-2004, 12:28 AM:

Sounds like pretty crappy theater design to me. Normally, in a large stadium house the screen may be angled upward a bit to provide a more direct target for the projector. Of course, the projector and console have to be mounted on some elevated and slanted platform to aim better at the screen.

It just sounds like this circuit did some real cookie cutter slap-it-together cheap design without actually doing any proper engineering.

This situation sounds just as bad (if not possibly worse) than the common dilema of keystoning in single screen theaters that were twinned. I've walked out of theaters and demanded refunds just as the trailers were starting to play when finding myself in an auditorium like that. If the projector is aiming toward the screen at any kind of angle (particularly a bad one when the port glass is near a corner in the room instead of the center of the wall) there's no way for the projector to gain any kind of focus. People just shouldn't have to watch movies like that at all. Only a fucktard bean counter could think that's okay to sluff off onto customers.

Posted by Will Kutler (Member # 770) on 07-31-2004, 12:35 AM:

In the all THX certified 20-plex (stadium seating) where I worked, horizontal keystoning was an issue.

In some auditoriums, the port window, audience and screen were not aligned to one another. On the smaller screns, the horizontal keystoning was somewhat noticable, but on a couple of large screens, not only was there keystoning, but due to the misalignment, although I was able to obtain the correct fl requirement, obtaining evenly illuminated screen was nearly impossible.

Posted by Paul Mayer (Member # 355) on 07-31-2004, 01:36 AM:

Vertical keystone is very noticable at the theaters I frequent here. Both the Brenden Palms and Century Suncoast are really steep and it shows, especially when the current THX snipe is run. That blue border line ends up not being anywhere near parallel to the screen edges. It looks especially bad at the Suncoast with their slightly curved screens. Yuck.

Posted by Robert E. Allen (Member # 1351) on 07-31-2004, 02:55 AM:

Years ago I worked the Granada Theatre in Ontario, California (a single screen with a high balcony) and the booth was about three stories up with the portholes about two feet above the booth floor. The screen was tilted up which minimized the keystone effect and movable side masking squared the picture. So even back then the designers knew how to compensate for it. Aren't they using theatre designers for the 'plexes today?

Posted by Carl Martin (Member # 1146) on 07-31-2004, 02:58 AM:

my very old theater has horrible keystoning on the main screen. formerly a single, now a triple. during a retrofit a few years ago, the flytower (yes, that old) was demolished, so the screen had to move in. the very back of the seating area was raised a little for ada reasons, which meant that to see the top of the screen under the former balcony overhead, the screen had to move down as well. it's very apparent on windowboxed trailers, but when there aren't obvious visual clues, the distortion isn't usually noticeable.

carl

Posted by Tim Reed (Member # 137) on 07-31-2004, 09:11 AM:

quote: Bobby Henderson
Of course, the projector and console have to be mounted on some elevated and slanted platform to aim better at the screen.

Usually, that's a case where the architect didn't know how to spot the portholes properly, and they have to get up and over the bottom of the window frame with the machine. Most consoles will tilt downward far enough for a pretty steep angle; it's just that the porthole has to be close enough to the floor for it to work.

quote: Robert E. Allen
Aren't they using theatre designers for the 'plexes today?

There aren't too many people around anymore who really know the score. Most new builds I was involved with, the architects didn't know from their rear-ends how to locate a porthole, or how to plot sightlines. If I was on the job early enough I could spell it out for them, but unfortunately, that was the exception.

Posted by Frank Angel (Member # 248) on 07-31-2004, 10:40 AM:

One of the worst retros I have ever seen was a local single screen that was quad-ed -- two screens in the original orchestra and two screens in the balcony, with a wall sliced right down the middle.

For the two balcony rooms, they just used the original seats and the same booth ports. This put the ports for each theatre in the topmost extreme corner, making the keystone this bizarre thing where the credits would dip to the one corner at the bottom of the image as if the projector wasn't level but as they crawled to the top would wind up higher, making it look like the projector was not level in the other direction.

As if that weren't bad enough, the screen was now centered in the "new" theatre but that was off-center to where the original screen had been. Problem was, they never install new seating....they just left the old seats as-is and of course that meant that they were aimed, not at the new screen, but at the imaginary old screen. So there you sat, pointed in the wrong direction.

The separation wall was straight while the original wall was angled and of course the floor was steeply raked and the ceiling also raked with a design that still pointed to an imaginary, nonexistent centerline. It wound up that every visual cue in the room was slightly off-center and tilted. It made you feel like if you didn't grab onto some solid railing or seat back you'd not be able to maintain your balance and you'd just fall over.

Cutting the theatre in half made each new balcony "theatre" a long, LONG narrow room with the screen still located on the stage but now with a "roof/floor" added from the front of the balcony to the screen, putting the screen literally the distance of the orchestra to the front of the balcony. This made it impossible to sit any closer to this new small screen than the entire length of the orchestra. If you sat in the back of the room, the screen looked like a postage stamp.

Did I mention that this long narrow room was not acoustically treated in any way whatsoever, so as far as speech intelligibility goes, if there were a number to measure it, it would be negative 100. You couldn't understand not a word that was being spoken....all you heard was echo. My girlfriend and I watched our first and last film there -- BLUE LAGOON -- luckily it was so bad that it was better if you didn't understand what they were saying.

And that, boys and girls, is an example of theatres DONE WRONG.

It is now a bank.

Posted by Edward Jurich (Member # 1787) on 07-31-2004, 07:11 PM:

Usually the old movie palaces had very high booths but also a long distance to the screen. The long distance helped reduce the keystone. A high booth and a large screen a short distance away is really really bad. Some of the auditoriums at the AMC here have really bad distortion from keystone and a curved screen

Posted by Bryan Fournier (Member # 264) on 08-01-2004, 12:03 AM:

Don't you just love those old "bowling-alley" auditoria.