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Author Topic: Lamp Flicker or (unstable arc?): noticeable during end credits Michael Moore Expert Film Handler Posts: 188 From: Dover, DE / USA Registered: Jun 2006 posted 11-04-2007 05:52 PM                        quote: Steve Guttag Now, how important the differences are to a audience that does not have the opportunity to compare the two Now this is what I was really getting at; I mean if I were to look at a projectors image and compare it side by side with another brand I may see a difference and I may not, who knows? But will the audience see the difference maybe, I'm not sure, but I would have to say the differences are subtle. Now as for my problem. I checked the voltage and it is 121 volts AC at every leg, one leg wanted to go to 122 then back to 121 but it was mostly 121. I then checked the Magnet and moved it up a little. I then took at look at the image again with out the lens. And I was confounded, I had just checked this thing a few days ago and it was not doing what I was observing. It was horribly out of focus, and instead of seeing uniformed light, all I could see is were heat waves rising from the bulb being reflected to the screen; and the light was dim. I then refocused the bulb and checked it for a few second with the lens in and I got it just right. Now I ran a film loop through with some credits and did not see any flicker what so ever. I also looked in at the arc and it was not dancing around as much. I then moved the magnet up a little more and I think I got it; the arc was quite still after this. Now that focus knob is very lose and I'm thinking it cranks it self out under vibration from the machine running. Is there a way to tighten this down? I'm going to put a mark on it and see if it moves after the show and note the credits again. Mike  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-04-2007 06:11 PM                     Yes, the Century focus tension can be adjusted. If you look on the focus assy (outside of the projector frame) you will see a small set screw (Can be slotted or allen)...it presses in on a piece of leather or like item to put friction on the focus shaft. A SLIGHT increase in pressure goes a long way. Again, you are looking on the operating side of the machine just about an inch back from the knob or about half-way between the knob and the frame casting. As to the shutter thing...I encourage you to look at many various types...you really will develop a preference for how some projectors look over others...even on that little aspect. Do customers? Not in the sense that they can technically describe why they liked or disliked the show...the story has a lot to do with that. However, it all adds in somewhere and as such I and others strive to always give the best show possible. Hence, I'm not as dismissive about such things as I DO feel it adds into customer enjoyment, even if a patron can't say "wow, your shutter really....yadda, yadda, yadda. But it all adds up. I have customers that have noticed a signficant improvement in a theatre where the real difference was the projector before and after. Steve  |  IP: Logged Michael Moore Expert Film Handler Posts: 188 From: Dover, DE / USA Registered: Jun 2006 posted 11-04-2007 07:42 PM                        Steve I think I did not specify hat I was talking about. the focus knob on the Kneisley not the SA.... I am almost done with the film. stepped into the computer room to check in, the credits are coming up in about 20 min. I now have a new bigger problem the flicker is actually worse. More towards the top of the screen, Once the bulb got up to temp, I tried to refocus the bulb slightly while projecting but it did not help, but it did not get any worse. I'm thinking I'm totally out of alignment. but that knob did move about 1/4 of an inch out. Mike  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 11-04-2007 08:53 PM                     Is your lamphouse exhaust working?  |  IP: Logged Michael Moore Expert Film Handler Posts: 188 From: Dover, DE / USA Registered: Jun 2006 posted 11-04-2007 09:16 PM                        Ok I finally figured this thing out with the input from all of you. First off my exhaust is working super well. That’s not the problem. Second I experimented with the magnet and came to a few conclusions Many of you will know this but I just figured this out. If you push the magnet right under the bulb (very close to the bulb) it will not strike and stay lit, Rather it will stick go out, stick go out strike go out, over and over, then finally strike and stay lit and flicker really bad then go out. If you move the magnet to the middle the bulb will strike and stay on, and you get flicker but not too much flicker. If you lower the magnet down as low as it will go the bulb strikes stays lit and does not flicker at all. If I removed the magnet all together the bulb would strike and stay lit but would have very bad flicker. If I installed it in reverse I got the same problems as having it too close. If I pivoted it from right while it was in the lowest postion the bulb would strike and the flicker would be at the left of the screen. And if I did it the other way the flicker would be to the right of the screen and if it were dead center the flicker would be just at the very bottom of the screen. If I pulled it up from the lowest position just a little, and placed it just off center to the left of the bulb the arc stabilized, and the picture had no flicker! Conclusions, I think every one of these lamp houses and bulb combinations would have a different setting and that there is no magic position or placement for the magnet. The user’s manual does not go into great detail about this either. The experiment also showed me that the magnet was not needed to start the bulb but rather to help keep the arc centered. I can't say it really stabilizes anything because if it were to do that the arc would be centered and stable. In my case the arc is slightly licking up and very stable, and production clean flicker free light. I think over time this is going to erode the edge of the anode. Anyone have some more technical insights as to what is going on here? Mike  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-04-2007 11:55 PM                     ...like the magnet on the old carbon arc lamphouses: Magnet in the same position in the area of the negative rod (cathode). Move the magnet left or right, the flame moves left or right. Move the magnet towards the arc or away from the arc and the flame will either be tall or short - and you didn't want a short flame for the flame would just "ball" around the electrodes and poor light was the result. As you mentioned: you removed the magnet and by doing this the current was at an even stream across the cathode (-) and anode (+) (as per the same with the carbon arcs..) and your light was not as good plus a lot of flickering. You put the magnet back to increase the negative current heading towards positive, thus causing the flame to increase and to create the correct burn.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-05-2007 06:25 AM                     The focus lock for a Kneisley lamphouse is the lock nut...which should be on the outside of the lamphouse. You adjust the focus via the black knob, and then lock it down with the nut. As to the magnet...its job is really to overcome the arc's tendancy to lick up...just like a flame. You should be able to adjust the magnet to get the arc pretty much centered and stay there for a long period of the lamp's life. The lamp may develop some anode sag, which can be minimized by lamp rotation. I've had better luck with non-rotation but lamps are hand made and some need more attention than others.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 11-05-2007 09:19 AM                        If you don't have a locknut, add one to the Kneisley focus (1/4" x 20) Warning: when you tighten this, the rear of the bulb will elevate slightly. You will then have to loosen the bar and lower it just a touch. Louis  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 11-05-2007 10:59 AM                     The support of the bulb, front and rear, with the reflector pivoting was a Osram recommended design with Kneisley followed for the construction of the Xenex I series. Locking nut is good to prevent focus shift, especially if you are tilting downward. We used to install (2) shaft collars with set screws and spring washers to take the play out of the focus thread. The support box which the lamp post is mounted can have some travel issues + the clamp to post and insulator beneath post are other issues which can effect squareness the "system". The magnet post may need to be bent slightly front/rear in addition to up/down and side to side to tame the arc. I had one of these Xenex I on a 70mm dome show with a 4000 watt bulb tilted at 25% up with the magnet bent forward with great results.  |  IP: Logged Michael Moore Expert Film Handler Posts: 188 From: Dover, DE / USA Registered: Jun 2006 posted 11-05-2007 11:08 AM                        I have to not tried to bend that magnet front to back. I'm not sure why i did not try that before. but good idea, I think that might help. I suspect maybe the bulb was made a little out of square, and round. I don't think the focus knob has a nut, I am going to add that too. I'm going to play with the magnet post ion more because I'm not happy with the post ion of the arc it is licking up and I'm sure this will lead to bulb failure sooner then later. Mike  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-05-2007 02:14 PM                     OH, there is one thing that I did forget .. being that you're using an ASL bulb and which was somewhat common with the ancestory of ORC and Perkin Elmers - which was the "sag" that the anode and cathode would get themselves into. Bulb sits in the horizontal position for quite the while and you can get "sag" from both electrodes. Take the bulb out, rotate the bulb by hand and see if the electrodes are in line with one another.  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 11-22-2007 09:38 AM                     I recently had two complaints of 'credit flicker'. In both of my cases it turned out to be the prints. To be 100% sure, I even checked it using another reel of film that I knew had a long white-on-black credit scroll and it ran flicker free. I notice the problem almost always seems to be on credit scrolls with small typefonts. I haven't been involved on the production side of films for some years but I think that many end-credits today are composed on video, and the problem seems to be caused by some interaction between the video rastering/rendering process and the scroll rate, and is most noticable on small type fonts. But as I said, this is sort of a wild guess based on some limited past production experience with video-to-film transfers. [ 11-23-2007, 02:05 PM: Message edited by: Jim Cassedy ]  |  IP: Logged Peter David Bruce Expert Film Handler Posts: 187 From: East Anglia -England Registered: Aug 2007 posted 11-22-2007 06:19 PM                    sorry to be silly... is the magnet the Y-shaped piece of metal the front of the bulb rests on?  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 11-22-2007 07:56 PM                     ..that's the anode support yoke. The rod magnet is that bar in the back below the cathode of the bulb, mounted on the lamphouse base of the mirror platform and is usually perpendicular (90 degrees) to the direction of the bulb.  |  IP: Logged Peter David Bruce Expert Film Handler Posts: 187 From: East Anglia -England Registered: Aug 2007 posted 11-23-2007 03:19 AM                    right okay. im still not used to seeing the arc and knowing where everything is in there. i have another 15hr shift today so i will have to take a look and see what i can learn. i had the problem the other day of it striking, going out over and over again then finally coming on.... i stepped up the amps which has fixed the problem.... but now i wonder whether it might have just needed some adjustment to the magnet etc.....  |  IP: Logged

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