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Author Topic: Projector speed issues Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 02-07-2004 04:01 PM                        I'm finally dealing with my "projectors were running too fast" issue... I've got V-4s; had to install new motors awhile back...and everything was running about 2-3% too fast. So: We installed Altivar Speed Drive Controllers last week... now I can dial in any speed I want (by varying the frequency to the motors). Question: How accurate should I be? After fiddling around today, I've got the projector running at 24.1 fps. Is that "good enough"? Or should I keep adjusting? Thanks, Jeff  |  IP: Logged Jeff Taylor Jedi Master Film Handler Posts: 601 From: Chatham, NJ/East Hampton, NY Registered: Apr 2000 posted 02-07-2004 04:27 PM                     At 24.1 fps you're already ahead of most of the rest of the world except telecine's running on synchronous motors. Hey, do you mean to tell me you were 2-3% too fast when I saw your 3-D setup?  |  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 02-07-2004 04:34 PM                        Most V5's I've seen run 2-3% fast, so if you've improved on that with your V4's, I'd say your doing alright. Afterall, you're within 0.5% now -- only 15 seconds gained over an hour. Now if you've got time on your hands to spend...  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 02-08-2004 12:35 AM                     Kinoton projectors without the 3-phase motors also run a bit fast. Steve  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 02-08-2004 01:18 AM                        Is there a "spec" for this? That is, how close are most studio screening rooms? Or the Motion Picture Academy? I want to be as right as I can... no point in having a private screening room if one cannot obsess about details... Jeff: I can't recall if you saw 3-D at our room before or after we burned out a motor... Jeff  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 02-08-2004 01:55 AM                     I'm a bit confused -- why is it hard to reach 24.0fps with your system? Insufficient resolution in the frequency adjustment? or lack of a strobe/photocell/oscope? (I think that hitting it to 3 significant figures is proably what you want to shoot for; in an optimal world). Probably a better way to look at it, though, is what your maximum frequency error is. Some quick googling suggests that an average human can detect approx. a 2 Hz difference around 400 Hz. So shooting for 1 Hz accuracy sounds good. 402Hz/400Hz is 0.5%, though 4002/4000Hz is 0.05%. If we assume the former is good enough (i.e. absolute Hz difference a human can detect falls off with frequency), then 0.5% of 24fps is 0.12fps. In short, your 24.1fps is probably good enough for 2 Hz accuracy, but not for 1 Hz accuracy. If you get to 24.0fps (i.e. as much as 0.05fps off), that's 0.2%, or 0.9Hz at 400Hz and 9Hz at 4000Hz. So, again, I would shoot for 24.0fps, which is barely under 1Hz error, but anything +- 1.2fps is probably good enough for most people. --jhawk  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 02-08-2004 10:20 AM                        Not difficult; time consuming. No, I don't have a strobe, so the only way to check it is to have a specific length of film and time it... at this point, I'm just curious what "spec" is, that's all. I agree that 24.1 fps will never be noticed by anyone... Jeff  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 02-08-2004 10:32 AM                     Jeff: gotcha...measurement methodology. Do use Newton's Method of successive approximation so you don't waste too much time with bad guesses. But best is to find a way to measure the speed in real-time. If a strobe is unavailable, also consider either a loop or short reel of a known-frequency audio track (e.g. 1k tone) with a frequency counter, or grab a photocell and a multimeter that reads frequency and put it after the shutter. Or a tachometer on a shaft. Or a shaft encoder+oscope if you're set up for dubbers. There are lots of ways If you don't have any of those tools, remember that photocells are only a few cents each. --jhawk  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-08-2004 11:58 AM                       Here's the easiest way. Print this out, and tape it to one of the sprockets (4 and 8 frame sprockets). Look at it under a florescent light, and adjust the speed til the pattern appears stationary... then you're at 24.00 fps (180 or 360 rpm shaft speed, actually). Be nice if sprockets came with these patterns etched in. (Bevan?)  |  IP: Logged Ron Yost Master Film Handler Posts: 344 From: Paso Robles, CA Registered: Aug 2003 posted 02-08-2004 12:48 PM                     It won't print-out .. all I get is the ILLEGAL PICTURE!!! thingy. I'd like to try it on my setup too. Ron Yost  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-08-2004 01:13 PM                       I just right click and select "Save Picture As". Once it's on your computer, you can print it out. And, if you can't right-click for whatever reason, the image is most certainly in your cache.  |  IP: Logged Ron Yost Master Film Handler Posts: 344 From: Paso Robles, CA Registered: Aug 2003 posted 02-08-2004 01:51 PM                     Thanks, Tim, but that's not how it works .. on my machine with IE6, at least. What's in the cache is "showpic.cgi ..." etc., with framestrobe.jpg at the end of the code. If I then copy that to another folder it turns into "showpic[1].jpg" which is the pic, though renamed somehow. Perhaps there's a setting in IE I need to change, but it seems odd to me that FilmTech is the only site I've encountered that behaves this way. Oh well .. I did get it to work and found my Brenkert is running a tad fast. Thanks for posting the dial, Tim. Ron Yost  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 02-08-2004 02:12 PM                       Sure thing, Ron. No problems right-clicking IE 6 here. You can make stroboscopic discs for anything you want to check the speed of (I made this one in Adobe Illustrator). The formula is: Bars = F x 2 x 60/rpm Where, F is the frequency of light used to view the bars in Hz. rpm is rotation of the object in revolutions per minute. If you come up with a value that requires a huge number of bars on the disc, you can divide it into even multiples to cut them down.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 02-08-2004 04:22 PM                     Jeff, thats a good laugh...really hilarious.....all these years you've been running at the wrong speed???? I guess thats what you get for running those POC. Tim, Bevan will be simply distributing the Kinoton stuff for projectors. We certainly don't need another belt driven wonder out there much less ANOTHER projector on the market. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-08-2004 04:38 PM                     Most projectors run off speed slightly all one has to do is try to run an interlock on two old Simplex or RCA or century soundheads with asyncronus motors and watch one running faster than the other to see the differences In fact speed differences was one of the origial concerns with digital audio sound  |  IP: Logged

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