Film-Tech Forum ARCHIVE: Top Down Masking

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Posted by Andrew Lee (Member # 1330) on 04-15-2004, 02:33 PM:

I am aware that some theatre chains are using a top down (or bottom up) single masking system as a cost saving measure. This entails the use of only one moveable masking curtain to alternate between scope and flat. As the centre reference obviously changes, the framing of the picture must be changed. I assume this is done by a small turn on the framing knob of the projector. I will also assume this moves the shutter (and possibly the timing) somewhat.

What is the general opinion out there when doing this? Is it something to avoid or is it alright as long as there is a "projectionist" making sure it is done right?

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-15-2004, 02:54 PM:

In a properly aligned setup you won't need to reframe the machine. Instead lenses are shimmed, or angled in the turret, so that your optical centre line is maintained, for flat and scope, right up thru the trap.

Posted by Andrew Lee (Member # 1330) on 04-15-2004, 02:58 PM:

Daryl, are there limits to doing it this way. At which point would you say "that's just too far to move the picture"?

Thanks

Posted by Robert E. Allen (Member # 1351) on 04-15-2004, 02:58 PM:

In a properly equipped theatre the 'scope and flat picture will be the same height. The 'scope picture will be wider. You don't need a top or bottom moveable masking (unless you're cropping the picture).

Posted by Scott Norwood (Member # 30) on 04-15-2004, 02:58 PM:

There is also something called "scissor" masking, where the optical centerline remains the same and the top and bottom masking move inward or outward at the same rate. This requires no adjustment to the lens collars or turrets. In a "normal" top-masking-only setup, one does need to re-frame the image slightly when changing formats. This becomes instinctive after a few experiences with a particular booth.

Regardless, top masking sucks. Or, at least, I feel strongly that the scope image should be the largest of any format. Except in 70mm houses, where the 70mm image should be even larger. My ideal masking configuration would be side masking for 1.66, 1.85, and scope, and the screen would get taller for 1.33 and 70mm. This is, of course, an aesthetic choice, so your mileage may vary.

Posted by Kyle McEachern (Member # 2250) on 04-15-2004, 03:05 PM:

The last two plexes that I worked at (15 and 12, respectively) had either 1 or 2 screens that used a top masking system. I always had a number of issues with it, and would prefer that it get avoided as much as possible, though my guess would be it's somewhat unavoidable in certain circumstances.

At the 15-screen, there was always a note on the framing knob, telling to go 1/8 of a turn when switching masking, and arrows indicating which way to go. As long as you did that, it would stay framed. However, my big issue was that this meant that flat movies were shown with a greater area of screen than scope movies. If flat had (Random numbers, not anything close to actual size) 20 feet by 26 feet, then scope would be around 15 feet by 26 feet. It's fine for the flat movies, but then the scope ones are painfully small, since these top maskings tended to go on what were already the smallest screens in the theatre.

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-15-2004, 03:22 PM:

quote: Andrew
Daryl, are there limits to doing it this way. At which point would you say "that's just too far to move the picture"?

Usually an auditorium with a really big screen has a decent throw, so it really depends on focal length. The shorter the focal length the harder it's going to be. I've had problems shimming the lens far enough with some compatively shorter throws (~45' width with ~32mm focal lengths), but other than that you can usually get it shimmed right on without any noticable distortion.

quote: Robert E. Allen
In a properly equipped theatre the 'scope and flat picture will be the same height. The 'scope picture will be wider. You don't need a top or bottom moveable masking (unless you're cropping the picture).

No need to crop the picture. Top masking (and bottom masking -- it's not cheap) is fully capable of presenting the full aspect ratio of every format. Unfortanately it is an evil required by the marketing hype of wall to wall (curved) screens.

A couple things I like about top masking is that it is usually more square than side masking, but more importantly, if you light your flat picture to accepted standards, you'll have one nice bright scope picture.

The downside is that watching almost any flat picture from closer than about midway through the auditorium is usually unbearable.

Posted by Richard Fowler (Member # 893) on 04-15-2004, 03:31 PM:

We did many cinemas with wall to wall image for all formats to satisfy customer requirements. Most lens turrets can be optically shifted or if there are 4 inch single lens barrel on the machine, then an offset corrector can be used. Reframing should be avoided since it makes an automated system not able to fully implemented...but projector design, lens, and skill of installation come into play. Schneider Optical lens program has a shift feature to check if your proposed lenses will work in an optically offset situation. We would all like to build cinemas with side to side masking but we are not paying for the client's mortage or rent [Wink]

Posted by John Walsh (Member # 168) on 04-15-2004, 03:44 PM:

How much the framing knob would have to be moved is a result of the lens focal length. Different people have different opinions of what is 'too' far, but I would not like to see the image have to be moved more than 0.100 inch up. I dislike the idea of having to move it at all, but the reality is often you are stuck with a situation and must deal with it. A theater we have (with a 90mm lens and a 60 foot throw), requires the operator thread one full sprocket out of frame for 'scope to position it correctly on screen. To clear the light from the lamp, I have seen two places where the brass trap (a JJ) was filed, and the heat baffle (a V8) had to be removed.

A suggestion (from a SMPTE article) is, when setting up the projector, is to properly aim the projector to project 'scope centered, and to move the frame knob 'off' for flat. The idea is both flat and 'scope are within the lamp 'spot' on the image. This doesn't solve having to move the framing, but does reduce the image moving far outside of the lamp spot, and going into the lens on an angle.

Posted by Ron Lacheur (Member # 1126) on 04-15-2004, 03:55 PM:

Is there any picture that is cropped using top masking?

Because the flat and scope are the same width? I'd imagine the scope would be smaller then it should be, or that the flat was stretched wider then its 1.85 ratio.

The complex closes to me uses all top masking. In some of the screens there, Flat is 5-6 feet taller than Scope while keeping the same width as scope.

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-15-2004, 04:01 PM:

Like I said above, there is no need to crop the picture. Top masking is fully capable of showing the full ratio of any format.

A 6' top masking travel would result in a flat screen of 49'x26.5' and a scope screen of 49'x20.5'.

Some people, who should be shot, have been known to crop scope down to 2.2:1 or even 2:1 with top masking. It's not necessary though.

Of course, I've seen some people crop scope down to the same sizes with side masking.

Posted by Ron Lacheur (Member # 1126) on 04-15-2004, 04:06 PM:

Cropping of any form should be ILLEGAL!!

It's definitely not in the best interests of presentation.

Posted by Mike Olpin (Member # 1115) on 04-15-2004, 05:13 PM:

In most of our auditoriums, we have a unique setup that utilizes both top and side masking. For scope, the screen stretches wall-to-wall and top masking comes down only a few feet. For flat, the top masking goes back up, and the side masking pulls in. This makes the screen appear large for both formatts, and creates a comfortable view for all seats, no mater what formatt is used.

We also have 5 auditoriums with top masking only. They suck. Not just because they make scope movies appear small, but also because they don't allow me to present flat movies in a complete and proper aspect ratio. The masking doesnt go high enough to show the whole picture.

Posted by Gordon McLeod (Member # 33) on 04-15-2004, 06:01 PM:

The push to stadium seated theatres effectively raised the hight of the room for a given number of seats leading to the push for vertical moving masking
It isn't ideal but is a fact of life out there
The biggest problem is light loss
The widescreen flat format is the least light efficient to start with compared to scope and making it the larger of the images is a tradeoff

Posted by Richard Fowler (Member # 893) on 04-15-2004, 06:02 PM:

Gordon, time to sell the auto focus kit for the xenon lamphouse [Smile]

Posted by Gordon McLeod (Member # 33) on 04-15-2004, 06:35 PM:

Actually the best idea was the Eprad squashable mirror that was in the universal lamphouse as it did increase the light output for 1.85:1 presentations
I have sometimes wondered about a inversion of the 70mm beam spreader lens but a beam squasher to get rid of the wasted light

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-15-2004, 09:25 PM:

I've wanted to try that too. There might be, otherwise non-existent, heat issues at higher wattages though.

Posted by Tom Wienholt (Member # 1510) on 04-16-2004, 12:01 AM:

For all you people that think that top masking for a scope movie is sooo terrible, then you are basically saying that a theatre should not put the biggest possible screen in each auditorium. I am sure that in auditoriums where this is done, the ceiling height is quite high and the auditorium is not very wide. So, in order to maximize the size of the screen, a large "flat" screen is used and then masked down for scope. This makes sense to me because the ceiling height in the auditorium is not wasted. Do you really think it would be better to use a "scope" wall to wall screen and mask the sides for flat to make a really small picture. I think that is stupid. Who cares if the flat picture is bigger than the scope. Am I wrong here?

Posted by Mike Perju (Member # 1482) on 04-16-2004, 12:15 AM:

Hi Tom,
The people who care if a flat picture is blown up larger than a scope one will be annoyed because the increased magnification of a smaller aperture will show up as very grainy on a larger, as well as any jitters from inproper printing will be a lot more disturbing(beign magnified more and all).
Other than that, in the perfect world it would make sense... :-)

Posted by Brad Miller (Member # 2) on 04-16-2004, 12:15 AM:

Tom, in a nutshell, yes you are wrong. [Razz]

I'll try and make this as simple as possible. Look at a scope aperture and compare it to a flat aperture. Scope gets *roughly* twice as much light (and film resolution) as flat does. So what ends up happening is when the smaller scope picture has enough light behind it to meet spec, the flat ends up being painfully dim. Plus image registration is greatly magnified, so flat films end up appearing very shaky.

The way to solve this problem is to build the theater properly in the first place. If the auditorium is wider, then you get all of the benefits from running with side masking.

Posted by William Hooper (Member # 71) on 04-16-2004, 01:12 AM:

quote:
In a properly equipped theatre the 'scope and flat picture will be the same height. The 'scope picture will be wider. You don't need a top or bottom moveable masking (unless you're cropping the picture).

With the exception of proscenium theaters. Most movie palace-era proscenium houses will have a proscenium opening of about 1.66, & best presentation maximizes the image size of all formats in the proscenium. Horizontal & vertical masking will both be required; otherwise, flat formats will look small, lost & disappointing to the audience.

Posted by Demetris Thoupis (Member # 833) on 04-16-2004, 02:44 AM:

Not always guys.
In Cyprus for example we have lots of cinemas which fir both scope & flat films to both ends of the wall but not TOP - Bottom. We have cases where the Flat fills the whole screen, but the scope is narrowed down (still projecting the full image and not croping it) like watching Widescreen DVD so that you understand what I am talking about. We even have one cinema which has the same image in BOTH flat & scope!!!! Fills the whole damn picture and looks well too. Anyway. I agree that the best way is to have full picture in TOP to BOTTOM for both Flat and Scope and for scope to touch both ends of the wall (left-right) where as flat to be in the middle. I want to ask something as well. What do you think is best to do when you have TOP - BOTTOM tolerance instead of Left - Right? (for scope films meaning) Considering that Flat fills all the screen in Top Bottom as well as left right while as scope is narrowed down like watching widescreen DVD on a conventional TV and fills only left right. What I always do is center the image in the middle of Top - Bottom. Some technician a while ago told me that is best to have it either on the very TOP or the very BOTTOM but that is not symmetrical I believe and is not good for the eye. If I take his advice then that means that for LEFT RIGHT tolerance I have the flat ALL to the right!! or all to the left!! [Smile]

NOT.
Anyway
Any thoughts?

Posted by Kevin Baglow (Member # 721) on 04-16-2004, 07:11 AM:

It all depends on the quality of the print. For example TRAVELLING BIRDS (the french doco.) was widescreen (flat) and looked 10 times better than MASTER & COMMANDER which was scope. I bring up the bottom mask and open the sides -slitely- for scope giveing me a bigger screen for widescreen (flat)

Posted by John Pytlak (Member # 331) on 04-16-2004, 08:42 AM:

Caring About Composition:

http://www.kodak.com/US/en/motion/newsletters/pytlak/spring2001.shtml

quote:
Scope" Is Meant to be Wider than "Flat"

Filling the full width of the screen for both 2.39:1 scope pictures and 1.85:1 flat pictures is almost as bad as "one size fits all" screens. This poor practice has become a popular trend in modern theatre designs, especially those with stadium seating. The misguided idea is to fill the front wall of the theatre with the biggest image possible, regardless of the intended format. So instead of maintaining the same image height for the scope and flat formats by using adjustable side masking, both formats are projected with the same width. The top and bottom masking are adjusted to letterbox the scope format, and actually project a much smaller image than the flat format.

What's wrong with this picture? Plenty! First, the wider 2.39:1 scope format is usually chosen to give pictures greater impact, than the more intimate 1.85:1 aspect ratio. Letterboxing it to a smaller image often violates the intent of the cinematographer and director in telling a big story.

Image quality of the flat format suffers in comparison to the scope format, especially when common width screens are used. The projectable image area of the 1.85:1 flat format is only 65 percent of the much larger and efficient scope format. It makes no sense to project the much smaller flat film image area on the print to a much larger picture than scope on the screen. It simply magnifies the grain and greatly reduces the light level. For example, a theatre that is getting the SMPTE aim of 16 footlamberts for scope on a 25 x 60 foot screen, will typically get only about 13 footlamberts for the less efficient flat format on a 25 x 46 foot screen, which is still within the tolerances allowed by the standard. But if they try to magnify the flat image to fill a 32 x 60 foot screen, they will only get a sub-standard 8 footlamberts, since the light must be spread over a much larger screen area. When you project flat and scope films to the same width on the screen, bigger is definitely not better!

Posted by Carl Martin (Member # 1146) on 04-16-2004, 09:15 AM:

as mentioned by several people, the real issue is optimizing the brightness for both formats. if that can be done, making flat and scope equally bright, then you're good. why make the flat image smaller than it could be solely to make the scope image larger in comparison? in the vast majority of cases, there won't be a side-by-side comparison; the whole program plays in one format. you wouldn't purposely make your flat image smaller than the scope image at another theater, would you?

but since the easiest way to keep the brightness consistent is to use movable side masking (between 1.85 and scope), that's the best way to do it. for the full complement of ratios, i like scott's solution, though i might want to make 1.66 taller than 1.85.

carl

Posted by Mark Hajducki (Member # 1732) on 04-16-2004, 10:06 AM:

Unfortunately out of the last 4 cinemas to be built in Edinburgh all of them have some or all of their screens top masked. As a result flat films are dim and shakey with scope films being shown smaller than the adverts and trailers.

What gets me more is that the screens aren't even wall to wall.

Posted by Sam D. Chavez (Member # 1841) on 04-16-2004, 10:13 AM:

The practice of using top only masking started when Scope was introduced. Long narrow houses with a proscenium had no easy way to show scope except to have a masking runner across the top and tilt the projector down for scope. I've always detested this practice as there were lots of scope pictures out in the mid '60's when I started out and the image was smaller than the 1:85.

I still remember my first theatre with this "feature". It also had a silver screen and the masking had worn a scratch on the silver paint and the area above the closed masking was also cleaner making the whole image disgusting.

However, we don't pay the rent as someone said. All we can do is recommend.

Posted by Evans A Criswell (Member # 381) on 04-16-2004, 02:00 PM:

I definitely prefer side masking, but over a year ago, Regal finished installing top/bottom masking in their smaller auditoriums. The image center stays in the same place in those auditoriums for both formats. Before this change, scope movies were shown at 1.85:1. Although top/bottom masking is not optimal, it's infinitely better than cropping scope to 1.85:1, which was done before the vertically-moving masking was installed in two-thirds of the auditoriums. One third of the auditoriums were built with side masking, but Cobb, in their infinite wisdom, chose 1.85:1-only in the others. Regal fixed it.

I can say that scope movies, although small, are very bright and sharp in those smaller auditoriums. I just sit closer when a scope movie is being shown in those.

I saw a scene from a movie recently in which top masking was obviously used in the auditorium in which the scene was filmed. Can't remember if it was "Win a Date With Tad Hamilton" or some other movie that had that scene. Has anyone noticed Carmike's current "fire marshall" trailer that shows side masking opening up on the screen?

Posted by Jesse Skeen (Member # 586) on 04-16-2004, 02:47 PM:

What are the "official" reasons for making screens this way? I've been baffled at a new theatre that opened last year that was built outside an older theatre that was torn down as soon as the new one was opened. They put top masking on all the screens, even the bigger ones! Of course the only reason I noticed this is because I know how this stuff works; they don't have it move during shows so most people probably don't notice it, of course the smaller screens look embarrassingly small in scope though.
The biggest problem I have with these screens is that in stadium theatres the picture is down low in scope, so it looks REALLY small if you're sitting in the top rows. Don't they take into account that scope is supposed to look BIGGER? With home theater getting better all the time this is NOT the way to get people out of the house and back into the theaters.

Posted by Brad Miller (Member # 2) on 04-16-2004, 03:19 PM:

Last month I converted a "fixed aspect ratio" auditorium to bottom only masking. This was chosen for three reasons...

#1 The auditorium was long and narrow so I needed to maximise the width of the screen as much as possible.

#2 Cost-wise installing either "top masking" or "bottom masking" was the same, however "scissor masking" was more expensive (and out of the theater's budget for the upgrade).

#3 Choosing "bottom masking" over "top masking" didn't change the eyeline for the line of sight like top masking does. (People don't have to look down when scope movies are run.)

I feel this is especially important in stadium auditoriums. Bottom masking is a better solution than top in almost every instance. However this doesn't change the fact that people should still be designing auditoriums initially for side masking to do it right.

I've never seen anyone use bottom masking before. Surely someone out there is doing it. Anyone see it done?

Posted by Paul Mayer (Member # 355) on 04-16-2004, 03:33 PM:

I've only seen bottom masking used in conjunction with other masking. The big screening theater on the Paramount lot comes to mind--all four sides are adjustable.

Posted by Antonio Marcheselli (Member # 373) on 04-16-2004, 03:56 PM:

We have several screens (usually smaller screens) that uses top or bottom masking. The main problem is the light on the image, it could be resolved connecting an electronic rectifier to the automation so that more light can be emitted when flat is chosen.
The position of the image is corrected using the lens' holder adjustment (V5). Of course in this case we doesn't use the len's adjustment to correct geometry but only to correct position.
The result is that the flat image is a bit dim, the geometry os not perfect but we don't have to move the frame at len's change (of any measure).

I personally found this solution good for very small theaters.

Bye
A

Posted by Adam Martin (Member # 641) on 04-16-2004, 04:11 PM:

Hmmm ... top or bottom ....

Anyway ... I once installed temporary *fixed* bottom masking to hide the negative splices in a French film for a festival. But that's it. Useless information, but I got to make the top/bottom joke. [Razz]

Posted by Carl Martin (Member # 1146) on 04-16-2004, 05:07 PM:

eventually we will get bottom masking in our 2 upstairs houses. this will work in conjunction with the side masking that we already have, but doesn't open quite wide enough for scope.

this will be ghetto-style bottom masking: a hinged panel which simply flips up for scope. should work fine, though, if it's set up right.

carl

Posted by Andrew Lee (Member # 1330) on 04-19-2004, 07:36 AM:

A few projects that I am working on in the future are indeed retro-fits that do not have the capacity for side masking. Yes, as said by all, if given the opportunity side masking of scope to flat is a no brainer. One project requires top only, therefore giving me no option on keeping the centre reference for scope and flat. Thank you for your replys. They have been most helpful.

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-19-2004, 04:51 PM:

BTW... if you can't shim the lenses enough, and aren't using consoles, you could always find yourself some adjustable table pedestals. Definitely beats playing with framing (or even shimming the lens), hands down.

Posted by Kevin Baglow (Member # 721) on 04-27-2004, 04:06 AM:

My bottom masking comes up. I have a 6ft curve in my big screen which complicates this. So far we can only change it manually before the show. We use steel upright supports every 6 ft along - holding a curved horrozintal rail that the black masking hangs from. The upright supports slide inside each other in three sections. Motorizing this would cost heaps.