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Author Topic: Top Down Masking Andrew Lee Film Handler Posts: 99 From: Oakville, Ontario, Canada Registered: Jun 2002 posted 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?  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 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.  |  IP: Logged Andrew Lee Film Handler Posts: 99 From: Oakville, Ontario, Canada Registered: Jun 2002 posted 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  |  IP: Logged Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 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).  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 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.  |  IP: Logged Kyle McEachern Expert Film Handler Posts: 165 From: San Francisco, CA Registered: Feb 2004 posted 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.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 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.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 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  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 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.  |  IP: Logged Ron Lacheur Jedi Master Film Handler Posts: 650 From: British Columbia, Canada Registered: Feb 2002 posted 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.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 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.  |  IP: Logged Ron Lacheur Jedi Master Film Handler Posts: 650 From: British Columbia, Canada Registered: Feb 2002 posted 04-15-2004 04:06 PM                     Cropping of any form should be ILLEGAL!! It's definitely not in the best interests of presentation.  |  IP: Logged Mike Olpin Chop Chop! Posts: 1852 From: Dallas, TX Registered: Jan 2002 posted 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.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 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  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-15-2004 06:02 PM                     Gordon, time to sell the auto focus kit for the xenon lamphouse  |  IP: Logged

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