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Author Topic: Frames per second differences? Kara J. McVay Film Handler Posts: 95 From: Delaware, OH Registered: May 2002 posted 01-12-2003 10:50 PM                        I have 1 Century and 2 Simplex 35 projectors. I recently took over operations of my theatre after an 11 year absence, anyway the Simplex 35's were not there when I left. www.thestrandtheatre.net has pictures. ( I still haven't gotten them to film-tech ) When we moved LOTR up to one of the Simplex 35's from the Century, one of my employees said "it will be over 3-4 min. sooner, because we moved it." I went WHATTTTTTTTTTTT ??? I am not that "motor savy", so my question is why does it run faster in my other booth? A little background on my booths. They are all separate locations (lots of fun), anyway, my balcolny & side theater booths are the Simplex 35's and the 1985 main booth is the Century. The balcolny is the original 1916 booth and the side was built in 1982. All I know about the electrical loads is that main & balcolny have 3 phase and side is still a single phase. Just wondering  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 01-12-2003 10:56 PM                     Do you notice a speeding up (or slowing down) of the audio when a print moves from one house to another? For the speed to be far off enough to shorten running time by 4-5- minutes the speed change has gotta be audible! Its also possible that the guy is blowing smoke... -Aaron  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 01-12-2003 11:00 PM                     It's a fact of life that not all projectors run at the same speed. Even two machines of the same model may not run quite the same. Oftentimes this is a function of belt wear and slippage. On a Century C with a poly V belt, you can speed-up or slow-down by at least 1 frame-per-second based on belt tension/slippage/wear. 3 minutes out of 178 (or 179, if you meant the Two Towers) is .1.7%, which is .408fps. That's well within the tollerances that you can expect. This is why people who interlock regularly use shaft encoders and synchronous motors/selsyns to ensure precise synchronization (generally for a dubber), or accumulators/elevators to take up the slack if the projectors are close. If you're sufficiently determined, depending on your equipment, it may be feasable to adjust for better accuracy. --jhawk  |  IP: Logged Kara J. McVay Film Handler Posts: 95 From: Delaware, OH Registered: May 2002 posted 01-12-2003 11:00 PM                        I have never noticed it any audible difference. I have witnessed the film being shorter. LOTR is 3 hours almost on the money with the preview I have on it, and it is a bit shorter...  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 01-12-2003 11:04 PM                     Kara, Over that length of film...3 plus hours.... the difference in speed would be pretty much inaudible. 3 to 4 min sooner is not that much faster over than length of time. I wouldn't worry too much about it..... Did you know that all British films were and may still be shot at 25 frames per second instead of 24??? All because of British Television being at a 50 cycle frame rate(interlaced)rather than 60 cycles like ours is. That way they don't need any special 2/3 pulldown movement like we have to use over here. Simplex 35's are a lighter load on the sound head/motor than a Century is, so the Simplex motors may run a bit faster. Mark @ CLACO  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 01-13-2003 12:07 AM                       If you have a Century soundhead with a poly-v (serpentine) drive belt, it is either loose and slipping, or it is riding up on the outside of the large pulley (possibly from a folded-over belt "v"). Either one of these conditions will make the projector run slow. Not enough to notice sound variations, but enough for a 3-4 minute difference in running time.  |  IP: Logged Leo Enticknap Film God Posts: 7474 From: Loma Linda, CA Registered: Jul 2000 posted 01-13-2003 01:45 AM                        I agree with the 25fps/PAL theory - as Mark points out, because of the 50hz scanning rate, telecine with PAL is simply a case of running at 25fps and scanning each frame twice. It's certainly not that uncommon to find cinema projectors over here which run at 25, usually ones which were formerly part of a telecine setup and then recycled for theatrical use. However, this would take a bit more than 3-4 minutes out of a three hour film. I'm still on my first coffee of the morning and not feeling up to complicated maths, but my memory is that the difference is 3-4 minutes in a two-hour film, 4-5 minutes in a three-hour film.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 01-13-2003 01:57 AM                     I think Tim has the answer. Poly-V belts do slip if you have that type of configuration. Also look at the name ID tags on the motors, and see if there is any difference in the motor speed. It might give you some idea as to what is going on.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 01-13-2003 02:04 AM                        An indoor house in our state ran a set of Century "C" projectors with R3 soundheads. Don't know if this was the original setup, but they had twin V-belts between the motor and the soundhead pulley. Some brain trust decided to replace them with something from a local hardware store, or the like. The new belts rode high on the pulleys and created a fast enough speed to be audible but not offensive to the owner's "tin ear". Ironically, when the machine was converted to those cog belts and brought back to proper speed, the owner's first response was disappointment that he wouldn't be getting out early anymore!  |  IP: Logged Stephen Furley Film God Posts: 3059 From: Coulsdon, Croydon, England Registered: May 2002 posted 01-13-2003 05:33 AM                     Mark wrote: quote: Did you know that all British films were and may still be shot at 25 frames per second instead of 24??? Mark, British films are normally shot at 24 fps, the same as 'normal' films in other countries. They are run at 25 fps for PAL video transfer, and live television transmission from film, in the days when that was done. Film material which is intended only for this use is sometimes shot at 25 fps, to avoid this speedup, in the same way that film intended only for NTSC is sometimes shot at 29.97 or 30 fps to avoid the 3:2 pulldown issues. The problem comes when you want to be able to transfer to both video systems, as is quite common, television distribution is no longer a national thing. Let's hope that if 625 PAL and 525 NTSC do get replaced by something better it will be by a single, worldwide standard.  |  IP: Logged Jean-Michel Grin Expert Film Handler Posts: 222 From: Geneva & Lausanne, Switzerland Registered: Jul 2002 posted 01-13-2003 06:12 AM                        For PAL technicians in Europe, NTSC means: Never Twice the Same Colors ! LOL  |  IP: Logged Leo Enticknap Film God Posts: 7474 From: Loma Linda, CA Registered: Jul 2000 posted 01-13-2003 06:22 AM                        ...and PAL means 'picture always lovely' I was once told a witty alternative acronym for SeCAM, but cannot remember it. As for a universal TV standard, you could argue that in some ways MPEG-2 has become that. Even though it is encoded in different pixel dimensions for PAL (720x576) and NTSC (640x480), the digital to analogue converters in DVD players and digital terrestrial set-top boxes are capable of displaying any sort of MPEG frame in a given TV standard. I'd guess that once analogue broadcasting is history, TVs will be like computer monitors: they won't be tied to any broadcast standard at all, and will display anything that the d/a converter chucks at it.  |  IP: Logged Brad Haven Master Film Handler Posts: 300 From: fremantle, West Australia Registered: Aug 2001 posted 01-13-2003 10:33 AM                     We have the same problem, our century projector (MDAW2) runs too fast, i'd say we would gain about 3 mins for a 95 min film, i can hear the difference myself, more so if i have run the film at the correct speed on our ballantyne, but we have never had a complaint. The next time we get some work done on our century i'm going to ask if we can get it corrected, it really bugs me, it sounds like the chipmunks at times! (exaggerated, but not far off!)  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 01-13-2003 10:50 AM                        NTSC = Never Twice the Same Color PAL = Problems Are Lurking SECAM = System Entirely Contrary to the American Method  |  IP: Logged David Stambaugh Film God Posts: 4021 From: Eugene, Oregon Registered: Jan 2002 posted 01-13-2003 11:17 AM                        Hmmm... In this thread I posed the intellectually stimulating question "How can you be sure 2 interlocked projectors will run at exactly the same speed?" The replies basically said "They just do". But this thread is saying the opposite is often true. ?? Just curious.  |  IP: Logged

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