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Author Topic: Couple of questions about Intermittents and Platters Shayne Martin Film Handler Posts: 1 From: Dallas, Texas, United States Registered: Sep 2003 posted 09-08-2003 05:42 PM                     I'm a new member to the upstairs world and since my arrival I've come across a few questions that I'd like answered. 1) I understand that the way the intermittent works is that the shutter spins in time well my question is, why does it flash twice before the intermittent spins once. 2)What causes the brain and platters to become... get to the point where they need calibration. We leave them on all the time so I don't understand what might cause some to go quicker than others or at all for that matter. I had a third but when I remember it then I'll write back later. Thank you.  |  IP: Logged Chris Hipp Phenomenal Film Handler Posts: 1462 From: Mesquite, Tx (east of Dallas) Registered: Jul 2003 posted 09-08-2003 06:01 PM                     That's a good question. I don't know.  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 09-08-2003 06:04 PM                     #1: if the shutter only blocked the light beam once for each pulldown, the flicker at 24fps would be horribly annoying, therefore the flicker rate is 48 times per second (projecting each frame twice), greatly reducing the visibility of the moving shutter blade. #2: It depends on the platters used. Some use mechanical switches and save for the switch or motors outright failing, they really don't 'go out of calibration'. In 'electronically controlled' platters like Christie, later Strongs, SPECO, etc., all electronics do drift with age and environmental conditions (temperature, humidity, etc) and as such the setting may drift away from the optimum. Also with many platters (Christie and SPECO come immediately to mind), the rubber drive wheels that move the platters wear with time and the speed that the platter moves does decrease proportionally. -Aaron  |  IP: Logged Chris Hipp Phenomenal Film Handler Posts: 1462 From: Mesquite, Tx (east of Dallas) Registered: Jul 2003 posted 09-08-2003 06:10 PM                     For a while, back when I was stupid, I thought that only every other frame was projected because of the shutter. What type of equipment are you using?  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 09-08-2003 06:14 PM                     Chris, all 24fps theatrical equipment basically uses the same system, even with variations on the theme like barrel shutters as on Motiographs and some Tokiwas, and single-blade shutters that rotate at twice the speed as on the Norelco AAII. -Aaron  |  IP: Logged Mike Blakesley Film God Posts: 12767 From: Forsyth, Montana Registered: Jun 99 posted 09-08-2003 06:17 PM                        Shayne, you better make that thread title more specific before you get yer ass moderated! Welcome to the forum.  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 09-08-2003 06:38 PM                        Don't worry Mike, I moderated his ass (changed the topic title). Don't forget about 3 bladed shutters, Aaron! Also, as far as platters are concerned, they are mechanical and will not keep exact settings as parts wear over extended periods of time. They need to be tweaked occasionally. But Aaron really answered the question best.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 09-08-2003 06:51 PM                     Shayne, when asking questions please be very specific as to the equipment you have in your booth. Few questions are so general that you can get a truly accurate answer without us knowing the brand and model of your equipment.  |  IP: Logged Torsten Jasper Film Handler Posts: 15 From: Braunschweig, Niedersachsen, Germany Registered: Aug 2003 posted 09-08-2003 07:01 PM                    quote: Joe wrote: Don't forget about 3 bladed shutters, Aaron! Yeah, don´t forget about 18 fps for soundless films. Greetings T. J.  |  IP: Logged Aaron Sisemore Flaming Ribs beat Reeses Peanut Butter Cups any day! Posts: 3061 From: Rockwall TX USA Registered: Sep 1999 posted 09-08-2003 08:53 PM                     quote: Don't forget about 3 bladed shutters, Aaron! How many 'standard multiplex' booths run machines with 3-blade shutters? I would say very few. quote: Yeah, don´t forget about 18 fps for soundless films. Once again, how many multis run silents anymore? What about 30fps Todd-AO? 60fps Showscan? c'mon guys... lighten up -Aaron  |  IP: Logged Thomas Procyk Phenomenal Film Handler Posts: 1842 From: Royal Palm Beach, FL, USA Registered: Feb 2002 posted 09-08-2003 11:29 PM                     What sort of difference does a 3-blade shutter make? Reduced flicker? =TMP=  |  IP: Logged Jon Miller Jedi Master Film Handler Posts: 973 From: San Diego, CA, USA Registered: Sep 1999 posted 09-09-2003 12:11 AM                     Yes, reduced flicker, but at a price of some loss of light. A three-bladed shutter would be just the ticket for an overlamped very-short-throw home system like some of us have, if you could only find one easily... (More lamp power than is necessary for a given screen size can cause flicker.) I think some commercial screening rooms use projectors equipped with three-bladed shutters to get a smoother image at a very short throw.  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 09-09-2003 12:27 AM                     It's been a while, but IIRC this is due to something known as Critical Flicker Fusion or CFF. There was a study that demonstrated that 50 flashes per minute is generally perceived by people as steady illumination. The test subjects could not detect any flickering. Mainstream cinemas play films at a speed of 24 frames per second, so if we doubled the flicker rate by using a two blade shutter then we would be approach the CFF. A three blade shutter raises the flicker rate to 72 per second which is considerably higher than the nominal CFF for humans. As mentioned, the trade-off is reduced light output.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 09-09-2003 09:05 AM                        CFF: http://webeye.ophth.uiowa.edu/dept/RESFELO/ResDay2000/puwat/sld012.htm http://www.therubins.com/alzheim/alztest13.htm http://www.physiol.ox.ac.uk/~pch/abstracts/arvo1998.html http://www.nlm.nih.gov/cgi/mesh/2002/MB_cgi?term=Flicker+Fusion&field=entry For most people, a film projected at 24fps with a two-blade shutter has acceptable shutter flicker at light levels below about 25 footlamberts. That is why standard SMPTE 196M sets an upper limit of 22 footlamberts for theatres. At higher framer rates, or by using a three-blade shutter, much higher levels of screen luminance can be used without significant flicker perception. I've projected 35mm prints at 80 footlamberts with a three blade shutter (72 interruptions per second), and the images are nearly flicker-free and stunningly realistic. But prints timed for the SMPTE standard 16 footlamberts may sometimes show too much detail in the shadow areas at this very high level of brightness. Assuming a 90-degree shutter blade, a two blade shutter is 50% efficient, and a three-blade shutter is only 25% efficient in transmitting light. So you typically need twice the lamp power if you move from a two blade shutter to a three blade shutter. One way to overcome this is to use a 5:1 "drive in" intermittent, or adopt the new Kodak "Quickermittent", that allow a more efficient wider shutter opening without travel ghost.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 09-09-2003 11:48 AM                        John, are the Kodak Quickermittents available as practical replacements for the more common 35mm projectors or is it just a design concept? I once tried to put in a drive-in intermittent in a Simplex XL. It sounded like a 120v coffee grider plugged into a 240v outlet. It was scary. Plus the picture had more jitter than a the normal intermittent. And, it wasn't a simple exchange of one for the other -- drive shaft gears had to be changed too. I gave up. Sure would be nice if the Quickermittents were just swappable with standards. I assume that with a Drive-in or Quikermittent, you then can cut back the shutter blades? I would imagine that in situations with large screens where they need more light (hence the desire for a quicker pulldown), they would already be pushing lots of light -- wouldn't the longer rest period bring the film closer to the threshold of heat damage due to the longer time light is passing through each frame?  |  IP: Logged

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