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Author Topic: Change the speed of playback? Adrian Hauser Film Handler Posts: 44 From: Sydney Registered: Mar 2008 posted 04-04-2008 06:29 PM                        Hi Film Tech, How does one adjust the speed of playback on a film projector. We have a Cinemeccanica Victoria 12 projector. We are performing butterfly tests with 1/2 the screen blanked to the film projector and the other 1/2 our Barco 2k projector in our Digital Grading Theatre. With the Barco set to 24 fps the projector seems to be running around 26 Fps. Adrian Hauser Sydney, Australia  |  IP: Logged Ron Funderburg Jedi Master Film Handler Posts: 814 From: Chickasha, Oklahoma, USA Registered: Nov 2007 posted 04-04-2008 06:55 PM                        Cinemeccanica's are belt driven machines it would be in the tension setting on the main drive belt but how you get it precise I'm not sure and if you actually match it the Digital out put I am also not sure. I'm not sure why it would need to be.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-04-2008 07:31 PM                     The best way to get a film machine to run at a particular speed is use a sync motor with timing belts (or direct drive) and then use a good grade of motor controller (one that has an accurate crystal...generally the cheaper ones don't). At that point you can have the machine run at any speed. I would have a good strobe light too (again with an accurate crystal) and shoot the strobe at say the shutter blade and verify speed. Now, if you are going to be doing a bit of this, then it would make sense to outfit the machine with a pulse-tack and a proper read out (with at least three digits). Steve  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-04-2008 08:05 PM                        THe absolute value of capacitors will affect the Cinemeccanica speed. More capacitors and a (large) variable resistor will allow some small adjustment. Years ago, 30 frame operation of a V8 required a new pulley which needed "half a tooth" more. We used a 1000 hz sound loop threaded under the 70mm film along with a frequency cou nter to get exactly 1000 hz. Louis  |  IP: Logged Adrian Hauser Film Handler Posts: 44 From: Sydney Registered: Mar 2008 posted 04-04-2008 09:11 PM                        Thanks for the thoughts on this. Ill check out our options early next week and initially look at the tension on the belt drive. I can change the frame rate of the Playback to the Barco as well so between the two I should b able to get a decent match. Louis, which capacitors should I be looking for? Thanks adrian.  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 04-04-2008 09:22 PM                     The V12 was their economy machine (based on the Portacine chassis) so a motor swap / crystal control with feedback encoder as Steve notes should do the trick....would be nice if there is a way to slave to the sync from your video / digital files with some phasing control to lock it in after a reference start point. I have used D.C. motors with 4 digit tach / encoder on a V-5 for playback to music / effects but it still required trimming every few minutes.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 04-04-2008 09:43 PM                     My experience is that 1k tone is often not 1k tone. A batch we have lying around was more like 1200 Hz The tone is intended as a level reference not a frequency reference, I guess. As for strobes, best bet is to check with a photocell/photodiode and an oscilloscope. --jhawk  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 04-04-2008 11:29 PM                       While it won't help you change speed, you can make a stroboscopic disc for anything you want to check the rotational speed of. I presently only know how to do this for 60Hz systems, but maybe someone else here can fill in the blanks. EXAMPLE: This is for a 4-8 frame sprocket (360 or 180 rpm shaft), 24.00 fps, viewed under a 60Hz light. I made this in Adobe Illustrator: When you place this particular disc on the end of the requisite sprocket and shine a 60Hz florescent light on it, the pattern will appear to be still if the projector is running at precisely 24 fps. If the pattern appears to rotate in one direction or the other, the speed is off. The formula to make one of these discs is: Bars = F x 2 x 60/rpm Where, F is the frequency of light used to view the bars in Hz. rpm is the target rotational rate of the object in revolutions per minute. QUESTION FOR THE MATHEMATICIANS... When you work the formula for 50 cycles, the result isn't an integer. How could a fraction be translated to the bars/spacing in a 360 degree pattern? There has to be a way to make this work on 50Hz.  |  IP: Logged David Graham Rose Expert Film Handler Posts: 187 From: Cambridge, UK Registered: Sep 2002 posted 04-05-2008 03:04 AM                     Gretings The easiest way to do digital grading/butterfly comparisons would be to junk the Vic 12. It is not up to the job. Buy a Kinoton ECII reference and lock it to the timcode output of the replay machine. Simple as that. No point buggering about with a Vic 12. From snowy Cambridge Goddnight David  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-05-2008 06:07 AM                     The ECII? While it is the finest studio projector, without question...for just putting out a picture at an accurate speed it might be a bit pricey. Kinoton also has the EQ series (quality inspection machines that also offer a Sony 9-pin option). The ES series, yet less expensive still have variable speed right out of the box (crate). Even the standard E projector can be outfitted with variable speed with readout. However, the fact remains, ANY projector with a sync motor and timing belts (or direct drive) can output a precise 24fps. By using the aforementioned motor controller solution, you take line-frequency out of the equation. Steve  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 04-05-2008 07:06 AM                     I agree with Steve... I used to use sync motors and variable drive units alot on my dailies setups. The more expensive units are pretty precise as for speed. Mark  |  IP: Logged Andres Briano Expert Film Handler Posts: 162 From: Buenos Aires, Argentina Registered: Jan 2008 posted 04-05-2008 09:41 AM                        quote: Tim Reed There has to be a way to make this work on 50Hz. As a matter of fact, Imax provides 50 and 60Hz pattern print outs to be placed on top of their platter decks for speed check and calibration. One cute little trick that a colleague of mine -you know who you are- taught me is to take the damping rollers further out (of allignment) so that your analog head reads perfs. Then, by plugging in an oscilloscope on your CP, you can know exactly at what speed you are running. NOTE: Since you are reading perfs and not frames, everything is multiplied by four. 24fps=96Hz. Andrés  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-05-2008 11:09 AM                     quote "Cinemeccanica's are belt driven machines it would be in the tension setting on the main drive belt but how you get it precise " Belt tension has nothing to do with it since cinemecanica use timing belts on every machine of theirs I have ever worked with (vic12 I have not used) Use a tach on the shutter or put a shaft encode on one of the sprocket shafts and use a frequency counter to get it dead on and a variable speed motor drive to adjust the motors speed  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 04-06-2008 10:02 AM                     Gord, The Vic-10 was direct gear drive. The only one to have that feature that was built in the 50's/60's as far as I know. Drum shutter aside,it was also their best attepmt at a projector IMHO. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-06-2008 12:46 PM                     I was referring to there belt drive machines  |  IP: Logged

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