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Author Topic: Century C left-side focus flutter John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 09-08-2007 10:40 PM                     Tonight we encountered a bizarre focus problem on one of our century Cs. Any suggestions much-appreciated. We found that a portion of the left side of the image would intermittently flutter in and out of focus. The effect was quite similar to having the main trap not properly closed. The focus flutter seems to occur on the order of 10Hz or so (hard to tell!). It's much harder to notice in scenes with motion, but the problem seems to come and go, sometimes consistently fluttering and sometimes disappearing for minutes at a time. The amount of the left image affected varied -- ranging from no visible problem to affecting about 4/7s the width of the image (starting on the left side). The problem gets substantially worse as tension is increased. With the tension backed off all the way the problem is minimized. At one point, during one reel, the entire focus of the reel shifted substantially and instantaneously (approx. 1/4 turn of the focus knob). [Supposedly] this did not happen during our previous screening. This problem might be completely unrelated. We see the problem with two scope lenses and two flat lenses, so it doesn't seem to be in a lens. The trap rails and gate have been cleaned repeatedly, and don't seem to show excess buildup (perhaps a little more than usual). There doesn't seem to be any significant hooking of sprockets, lateral play of sprockets, and the reference guidance roller seems to function properly. We noticed the problem for real for the first time tonight, during a scope movie, but upon further consideration, realized we had seen it before. Our trailer reel has had some bizarre focus issues the past few shows, but we had attributed them to something specific to those individual trailers (embossing, odd printing, etc.). But on reflection, it's the same problem. Not clear why we didn't notice it on prior features...presumably it was less severe. It seems to be independent of film stock. We're running 2k Osram lamps in Xetron XHN2000 lamphouses, and there does not seem to be any hotspotting. The effect is not visible without film. The lamps are being vented with 400CFM and there is no excessive heating of the lamphouses or the projectors. Any tips/thoughts/suggestions? At times the problem seems to approach unwatchability. Throw is 80 foot, lenses in question are all Isco Cinelux ultra-MC (gold). It seems a bit more noticable through the scope lenses (125mm focal length) than the flat lenses (80mm), which seems counterintuitive to me (less magnification with scope). Thanks again. --jhawk  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 09-09-2007 02:03 AM                        is the gate closure set properly? if it doesn't close far enough then the film might be riding up the bevel of the lateral guide roller on one side. that could account for a 1/4 twist of the focus knob. if it vacillates that could be the flutter. increasing tension might further incline the film to ride up in this manner. if that's the case, the gate tension on this machine is bound to be set higher in general. we have sa's but i assume the c is similar enough.  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 09-09-2007 02:42 AM                     Hi John Is it every print or just the new one? I'd check the gate rails haven't moved. Move them out as far as they go and try again. Any chance you've got someone in there that likes to fiddle? John  |  IP: Logged Scott Balko Expert Film Handler Posts: 136 From: Redwood Falls, Minnesota, USA Registered: Apr 2000 posted 09-09-2007 08:17 AM                     If your machine still has the studio guides, get rid of them. The lateral guide rollers are all it needs. Sounds like it's squeezing the film in the trap, and the more tension you impose just forces it into the already too narrow space and curls the image area.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 09-09-2007 08:17 AM                     Check that the studio guides havent got shifted and the film is too tight of lateral pressure in the trap. Also check the guide rollers are not to tight and snap back and forth freely as the film can climb out of them Also check for wear on th the gate rails and you could reverse them if the other side isn't worn  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 09-09-2007 08:30 AM                     Thanks for all the advice. Clarification, the major instantaneous focus shift recurred in the same place at the next show, so I think that's just some unrelated print issue. We'll double-check the studio guides to make sure they're as far out as possible. It seems to be every print (at least it is the two prints we have right now, as well as a smattering of trailers; both prints on 2383, btw). Hmm. Gate closure...I hadn't realized that was adjustable. Will hunt and check. The film doesn't seem to be riding oddly. Scott, by "trap rails" I mean the spring-loaded rails, not the studio guides. Swapping the trap rails from another projector doesn't seem to affect the problem, so I don't think it's a wearing problem on them. The reference guidance roller springs freely as it should. Thanks! --jhawk  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 09-09-2007 10:27 AM                        30 years ago we installed an 8-plex with 6 SA and 2 "C" century. The C 's were straight gates. Every show, the film "popped" fully out-of-focus at the same number of minutes from the start. A curved gate conversion kit stopped the problem instantly. Has something recently changed in your installation? New reflector? Larger bulb? Louis  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 09-09-2007 01:10 PM                     Nope, no recent changes. That's what makes it so weird... --jhawk  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-09-2007 06:40 PM                     I agree with Scott... Start by trashing the studio guides... worthless pieces of metal! This holds true for ALL Century projectors! If you are using no larger than a 2kw lamp and have either a good dichroic reflector or good heat filters the straight gate will work fine. Over a 2kw lamp then you really need a curved gate. Mark  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 09-09-2007 07:19 PM                     Well, adjusting the outboard studio guide to its extreme travel seems to have indeed solved the problem (at least, so far...). THANKS! (I'm thoroughly mystified why this was never a problem previously and how it suddenly became one...). Dumb question: what's the minimum disassembly necessary to actually adjust the screws that hold in the studio guides? I managed to sneak a right-angle screwdriver in just enough to loosen the operators's-side guide (the one I needed), but afterward I couldn't get the screws very tight...what's the right way to get access to those screws? All this time I had naively assumed the studio guides were at their outer limits, since we'd never had any issues of this sort...live and learn. Yes, it's an original straight gate with a 2k lamp. We have not had focus issues previously, so I think we're ok on that... Thanks again, everyone. --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-10-2007 09:13 AM                     Take the trap out and adjust/remove them (I keep them in but ensure they can't touch the film). To take the trap out...you will need to remove the light shield (two screws) and then the trap, three screws (in triangular formation). There are pins so you should get it back in exactly the same spot. Steve  |  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 09-10-2007 10:54 PM                        quote: Mark Gulbrandsen Start by trashing the studio guides... worthless pieces of metal! This holds true for ALL Century projectors! If you are using no larger than a 2kw lamp and have either a good dichroic reflector or good heat filters the straight gate will work fine. Over a 2kw lamp then you really need a curved gate. Hmm, at the drive-in I was considering replacing our Super Lume-X lamphouses running 2.5kW lamps with a pair of X-60Cs and 4kW lamps. Is this not recommended with water cooled straight gate Century CCs?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-11-2007 09:23 AM                     I am pretty sure that you'd have alot of film flutter making focus all but impossible. I thought you installed one of the Technilite kits there... Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 09-11-2007 10:11 AM                        The Century C's I mentioned above: focus popped with a CXL-10 bulb in CH-10 Christie consoles. I agree with Mark: above 2000 watts in a good/great reflector, you will need curved gates, probably with water. According to Strong: S. Lumes/2500 watts and X60D with 3000 watts have within 1% the same Lumens. It would logically follow that 4K would only be slightly brighter. Louis  |  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 09-11-2007 06:23 PM                        quote: Mark Gulbrandsen I am pretty sure that you'd have alot of film flutter making focus all but impossible. I thought you installed one of the Technilite kits there... Different drive-in. Although 4 years later and I'm still not sure I can see the huge difference I'm supposed to be seeing at the other drive-in. The picture seems to be blue-er though, which is nice, I like blue. quote: Louis Bornwasser According to Strong: S. Lumes/2500 watts and X60D with 3000 watts have within 1% the same Lumens. It would logically follow that 4K would only be slightly brighter. Well, scrap that idea. Thanks guys, saves me wasting any time on that.  |  IP: Logged

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