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Author Topic: FP20 running slow Michael Harlow Expert Film Handler Posts: 170 From: Faversham, Kent, UK Registered: Jul 2002 posted 02-10-2003 09:13 AM                     I appreciate that this may be an odd question, but how can i tell if my projector is running slow?  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 02-10-2003 09:32 AM                        Easiest way is to measure out an exact length of film, and use a stopwatch to time its passage through the projector. For example, 1440 frames should take exactly 60 seconds to go through the projector. (24fps x 60 = 1440) You could also time a known length loop through the projector. For example, a 120-frame loop should have the splice go around every 5 seconds, or 12 times per minute. The other method would use a calibrated strobe to verify the shutter RPM.  |  IP: Logged Leo Enticknap Film God Posts: 7474 From: Loma Linda, CA Registered: Jul 2000 posted 02-10-2003 09:35 AM                        True, but over a length that short your reaction times on the stopwatch button could easily make it inaccurate over a second or two. I would be inclined to run a feature through the suspect machine and time its duration to the nearest second. Then put the same print through another projector which you know to be alright and do likewise. If there is a significant discrepency between the two times (as in, more than a couple of seconds), that indicates that the two projectors are running at different speeds. The difference between 24 and 25fps is around 4 minutes for a two-hour feature, so this method should show up differences of more than half a frame per second very easily. Over an hour or more, the odd second here or there will not skew the reading significantly.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 02-10-2003 09:46 AM                        quote: ...but over a length that short your reaction times on the stopwatch button could easily make it inaccurate over a second or two. Hopefully someone skilled in using a stopwatch isn't in error by that much!  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-10-2003 10:26 AM                        Another - again, somewhat imprecise - method which will reveal more drastic problems is to run a 1 kHz loop and then use a tuning device to measure the pitch of the output. For instance, if the projector is running at 22 fps, the frequency will be around 915 Hz.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 02-10-2003 01:16 PM                     I think John's methods are the only really good ones. Stopwatch measurement should not be off by more than 250ms or so. Anything else is criminal. Leo suggests using a "known good projetor." Unfortunately there's no such thing. You would be surprised how many projectors are off by just a little bit. Unless you measure it, don't presume a baseline, because chances are you'll be wrong. Michael suggests using 1 KHz tone. Unfortunately, 1 KHz tone is generally not at 1 KHz. It's designed to be a gain reference around 1 KHz, but my experience is that it may be significantly off from 1 KHz (e.g., around 50 Hz off). --jhawk  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-10-2003 01:33 PM                        True, but you can check that. If you have a FP30E within reach, you can run the test loop and check its frequency. The FP30E are usually very reliable. Generally, I found the 30 series Kinoton machines very stable. We have often used them in multiple interlock situations and the - I don`t know the proper English term - "gallows" which you have between the machines never moved up or down. edit - I just thought of another method: Prepare a known length of film. Add some material at the beginning to allow for the speedup time of the projector. Make a hole on the soundtrack of the film, and another a known length of film later. Record the output on your notebook. Then you can see exactly how big the time span between the two pops is.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-10-2003 02:01 PM                     I don't think a stopwatch would be that inaccurate. Allowing for human lag time while punching the stem, the lag time will be the same at the start as it would be the finish unless you had an "itch" to tend to... Seriously, reaction time would be very consistant although it would probably vary from person to person. However, the end result would still be consistant. If you analyzed that, the old carbon arc operators were very consistant in hitting the motor and changeover cues almost right down to the split second.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 02-10-2003 02:13 PM                        Once upon a time, people and stopwatches were considered accurate enough to time short athletic events, even for world records. Those times are recorded as "official" in the record books. The error in timing a 1-minute run of film with a stopwatch is probably negligible. You could always time a longer run, or take the average of several runs.  |  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 02-10-2003 02:24 PM                        If you believe that only a computer can be accurate, you could always hook up a DTS-6AD to the machine and just check the film speed registered by the DTS reader. I however believe that you should easily be able to be within a quarter of a second. Unless of course you're doing a physics lab and need a source of error.  |  IP: Logged Rick Long Jedi Master Film Handler Posts: 759 From: Toronto, Ontario, Canada Registered: Nov 1999 posted 02-10-2003 04:06 PM                     Back during the Sensurround installations (when the speed of the projector (and thus, frequencies derived from the film to trigger the system) had to be reasonably accurate) we used John's method of the 7 1/2 foot loop. As John points out, it should pass a given point in the projector every 5 seconds. Leave it run for a couple of minutes or so, and you should hear the splice at the same point on your watch. (5, 10 15, or 2, 7, 12, ect.).  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 02-10-2003 05:42 PM                        quote: If you believe that only a computer can be accurate, you could always hook up a DTS-6AD to the machine and just check the film speed registered by the DTS reader. How? BTW, a quarter of a second is six frames. That does not strike me as particularly precise.  |  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 02-10-2003 05:56 PM                        Hey, jhawk mentioned the quarter second first (250ms). I just said that would be easy to do. I know I can be far more accurate with a stop watch. As for the DTS-6AD displaying film speed. I can't remember what software revision it first was added to but I know that it is included in a system that has the following versions: CPU V1.06 DSP controller V1.03 DSP firmware V1.10 Projector (film) speed is listed under the STATUS menu.  |  IP: Logged Karen Hultgren Master Film Handler Posts: 492 From: Agoura Hills, CA, USA Registered: Mar 2000 posted 02-10-2003 07:19 PM                        Michael, Because the DTS players use a phase lock loop (PLL) to lock the timecode to the projector speed (motor), you can also check your projector by using one of our test/setup discs that have a 1k Hz tone. Turn off the projector's motor and insert the disc into the DTS player. Measure the output of the DTS player using a 4-digit frequency counter. Note the frequency and then turn on the projector's motor. You should see a difference on the meter. If in the USA, your projector should be running at 24fps which will be show up on your meter as 1K Hz. You can allow for about a 20Hz difference. You may also use the DTS-6AD 'STATUS' screen to see projector motor speed (this also uses a PLL). The screen will tell you how far off your speed is, using 24fps as reference. Karen at DTS khultgren@dtsonline.com  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-10-2003 09:11 PM                     The other method is to put a foil across the loop of film and then put a frequency counter on the proximity cue detector  |  IP: Logged

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