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Author Topic: Slow Projector Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 08-04-2006 02:44 AM                       quote: Ron Yost there was a pic of a strobe dial posted .. I have it, but can't remember who made it. That was me. quote: John Pytlak a projector shutter shaft is likely too fast (1440rpm) for that technique to be accurate. The traditional method is to stick them on a sprocket, as Frank mentioned.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 08-04-2006 04:33 AM                        quote: Mark Gulbrandsen Recently it helped us big time on solving a Simplex 1060 scratching problem. you couldn't see it scratch film with the naked eye but the problem was very easy to see happening with the strobe. How did that help you find the place where the scratching occurred?  |  IP: Logged Ron Yost Master Film Handler Posts: 344 From: Paso Robles, CA Registered: Aug 2003 posted 08-04-2006 12:04 PM                     Thanks, Tim! It did later pop into my foggy ole' brain that it may have been you. Ron Yost  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 08-04-2006 12:37 PM                     Using a strobe helps freeze an image when used in situations such as surface or base scratches.....have used this on cameras and optical printers. In addition to strobes, I use an LED display box, when viewed through shutter, checks for speed and forward or backward drift.  |  IP: Logged Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 08-05-2006 02:02 PM                        If you change the speed in which the projector runs wouldnt you also have to readjust the analog sound optics and or slit loss eq?  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 08-05-2006 03:14 PM                        No. Slitloss EQ is for focus, it has nothing to do with the speed. Theoretically, if you change the speed, the frequency response and therefore also the HF range change, but the slitloss adjustment is relative anyway, not absolute. One could argue that if the projecor is made slower, some of the highest frquencies would drop, but so do the frequencies in all other bands and the difference is so minimal you can't probably even see it on the analyzer. Plus it's again relative response=flatness of response, not an absolute HF target that is aimed for. quote: Richard Fowler Using a strobe helps freeze an image when used in situations such as surface or base scratches. How? Sorry to be so slowbrained here, apparently it is something very obvious that I am overlooking, but I don't quite understand the connection and application of the strobe disc here.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 08-05-2006 03:43 PM                     Richard doesn't mean the disc, he means an actual strobe light, aka stroboscope. --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-05-2006 05:33 PM                     Michael, The reason a strobe helps is the same reason movies work at all...persistance of vision allows movies to work with our eyes....however this same persistance of vision will keep you from seeing things clearly like film touching where it shouldn't. Lets say you have the film buckleing such that it periodically bellies forward and rubs its face on a gate part...but it happens for less than 1/24 of a second and only on pull down. Your eye will never catch it. Now use a strobe...with a strobe you can effectively "slow down" the projector yet still maintain the exact same operating conditions...then you will see in slow motion what is happening to the film as it travels. Depending on how regular the incident occurs, you can even freeze the film while it is making contact. While I have not used a strobe for this sort of investigative work, I can see how someone might. I personally prefer the red Marks A Lot approach...Run a loop of virgin film...locate the scratch in question on the film....fill in the scratches with the red marks-a-lot...run the film again (keep the orientation and framing the same)....look for the red dust trail...it will point you to the culprit just about every time. Want to see how smooth your machine is...that is when a Strobe comes in handy...you'd be amazed at how jerky most shutters run (think about all of the gear lashes between the motor and the shutter, and all of the frictions and different flywheel effects or elasticity of the belts)...it all adds up in the shutter. Just be very careful when working with a strobe...Objects ARE spinning faster than they appear! Steve [ 08-05-2006, 08:07 PM: Message edited by: Steve Guttag ]  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 08-05-2006 11:43 PM                        That reminds me, one of our projectors has a slight hesitation in the intermittant about 1/2 way through it's pull down, when rotating the motor by hand. The others don't. The projector is louder, the normal purr is a bit more edgey, but not by much, and that can be mostly attributed to the style of gate. It's a strong, don't remember the model number but from early 80's. It uses and older style flat trap and gate, the kind with the spring loaded bars on the gate and a rigid trap, rather than the curved kind with the rigid gate, and thin bands in the trap. The gate seems to add the noise, the picture seems fine. It's been running fine. I think it just may be a worn intermittant that has a little play in it, probably should be replaced on next PM visit. I'm definatly going to alert the tech when he comes by, but do you think this is an urgent issue?  |  IP: Logged

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