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Author Topic: Century SA focus shift John Westlund Expert Film Handler Posts: 204 From: Burney, CA, USA Registered: Jun 2001 posted 04-15-2003 06:57 PM                     I just got a new flat lens. (One of the ones that Paul listed in the equipment for sale forum. Its great and thanks Paul). Well when I installed it I noticed the focus was razor sharp on the left side of the screen but fuzzy on the right side. I installed the scope lens and noticed the same thing. I rotated the lens and the focus problem stayed on the right side. I had recently installed new gate bands. I also tried replacing the whole gate and trap assembly from another SA and that didnt change anything. Time to come to the experts. Thanks Guys. John  |  IP: Logged Mike Pennell Expert Film Handler Posts: 150 From: Tucson, AZ, USA Registered: Apr 2003 posted 04-15-2003 07:23 PM                     I had the same problem, but instead of left/right focus problems it was top/bottom. The lens mount assembly had come loose. Straightening it out and retightning it solved the problem. But it sounds like you have a turret, whereas I did not. Hope this helps.  |  IP: Logged John Westlund Expert Film Handler Posts: 204 From: Burney, CA, USA Registered: Jun 2001 posted 04-15-2003 07:36 PM                     Sorry, I should have clarified that I do not have a turret.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-15-2003 07:49 PM                     John, I recall seeing once that the lateral adjustment of the lens holder was locked down tight while I was in the field. Seems as though the operators tried to focus with that lateral adjustment locked down. The lens housing moved ok, on the bottom only. I wonder if somewhere that happened to your machine before you got the machine. There is a distinct possibility the whole lens holder is sprung. If it is, you are screwed. A new one would be in order. I don't know if there is a way to un-spring it. Try this: As you turn the focus knob from one extreme to the other, see if the inboard side and the outboard side of the lens holder moves by the same amount. It should. If it does not, there is a bind somewhere. Then, use a machinist's ruler to see if the inboard side of the lens barrel distance to the projector casting is the same as the outboard side. If not, you found the problem. All that is left is to find out what part is actually bent or sprung. Edit: I wonder if there could be a problem with the support gib being improperly seated or sprung, or maybe the screws holding it to the main casting are loose......I have seen this machine of John's - it looked like a rebuilt of the rebuilt's rebuilt. However, it is a nice looking machine. It could have orginally been a "cobble" job.... I had a Simplex XL that gave exactly the same indication John is experiencing. In my case, the P-1633 studs on the P-1621 Film Trap Door Support Bracket were sprung.  |  IP: Logged John Westlund Expert Film Handler Posts: 204 From: Burney, CA, USA Registered: Jun 2001 posted 04-16-2003 01:41 AM                     I checked this evening and the lens barrel moves smoothly and looks to be moving the same amount on top, bottom, left, and right.  |  IP: Logged Dick Prather Master Film Handler Posts: 259 From: Portland, OR, USA Registered: Feb 2002 posted 04-16-2003 03:27 AM                     John, Can you focus through and get the right side only to focus? Have you tried the lenses in another projector? If so it sounds like the trap may be off a little bit. The SA has a bronze alloy for the dovetail and film trap body. I have seen these slightly bent so that the trap was not perpendicular to the lens assembly. That adjustment, if needed, needs to be done very carefully to not break something. Check and see that one or more of your studio guides is not pinching the film. That might cause a problem like you discribe. As Paul stated check and see that all the assemblies are fastened properly to the case. If so use a square to try and see if one or the other is off. Using a small shim under one side or another may also help. Work on one assembly at a time. Best of luck.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 04-16-2003 07:13 AM                        I have had success using a shim on one side or the other of the solid rail assembly. I assume you have cleaned both bands and rails thoroughly (scrape off hard deposits with a non-metallic tool, then use a stiff bristle toothbrush), and the band tension is equal on both sides. Use the lowest tension that gives good steadiness. Check alignment of the film through the gate, misalignment or "pinching" by the studio guides can cup the film. An alignment jig is available.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-16-2003 09:17 AM                     OK, let's review the check list: 1. The focus problem is present on both flat and scope movies. 2. New replacement band set has been installed. 3. The lens was rotated and the focus problem did not follow along with it. 4. Shims were tried in one side of the solid rail assy. 5. Lens holder moves smoothly without binding. 6. Proper fastening of the gate parts to the casting. 7. Adjustment of band tension had a small effect on the focus. 8. Xenon lamp alignment seems to be OK. 9. Different trap shoe and gate assembly was tried in this machine. 10. Machine is not equipped with a turret. Questions: 1. Was a magic marker used to "paint the rails" and a loop run through for a few minutes to check the wear pattern on both the shoe and bands? 2. Did you check to see if the lens holder is square with the projector casting? 3. Did you install the shoe upside down and run a test loop to see if the focus problem shifted to the other side of the screen? 4. Did you "sneak" the film trap open just a slight bit with the projector running and see if the focus change was even across the screen? 5. When the bands were installed, did they properly align with the small dowell pins so they could not cock to one side or the other? 6. What is the positioning orentation of the four screws that holds the light tube (the part that has the trap release knob) with respect to the elongated holes in that assembly? 7. If you focus in the center, how far out oof focus is the sides, and are mis-focused equally? Comments: 1. Dick Prather mentioned the dovetail slot for the for the film trap body. If the trap is not perpendicular to the lens assembly, there will be a definate focus problem as you described. 2. Dick also mentioned the studio guide. Since you have a Century SA, I would presume Dick is addressing the lateral guide roller as well as the studio guides themselves. If so, pinching of the film could cause a focus problem. 3. John Pytlak again mentioned the shim procedure. I suggested the use of a matchbook cover. When you tried it, what was the focus change from before and after? Was it better or worse? 4. John also mentioned to check the band tension on both sides. That is an excellent idea. 5. John also mentioned a mis-alignment of the film path. It would be well worth inspecting. More suggestions: Check the gib to make sure it is not warped. Dick mentioned the use of a square to do that. I can see the gib getting sprung because of the recoil of the gate smashing the film trap assembly when closing. Allowing this to happen is a common problem most projectionists seem to forget about. If something is slammed closed hard enough and long enough, something is going to get sprung. The coil spring in the gate closure mechanism may be set wrong which will aggervate the problem. I have seen some so tight that if a finger somehow was in the way when the gate closed, it would give you a nasty blood blister on your skin. I set mine so the gate will close and seat smoothly without slamming. There is a distinct possibility the gib is warped or as Dick mentioned, the dovetail could be warped. Another possibility is the light tube is actually too close to the gate. What I mean by that is, when the gate is closed, it might be bottoming out one of the bands. Also, try this: Put film in the machine,and bar it through by hand. When the starwheel indexes and starts its pull-down, how much resistance do you feel on the motor? Then do the same without film. I am sure you will feel some resistance on pull-down, but with film in the machine it might feel more like a bind. If the resistance is excessive, I would definately suspect you have a very tight gate. Then sneak the gate open just a little to remove tension, and see if it feels better. Of course without film, it'll probably roll nice and freely. If the gate is really crushing the film, that could account for the thrust changes in the pinion shaft of the soundhead. Also, it would probably not pass poor splices without losing a loop or two. I am starting to get convinced the problem will be found in the actual positioning of the light tube, a bent dove fit in the film trap, or the gib is sprung. Also when you focus nice and clear on the left side of the screen, which way do you have to turn the focus knob to focus the other side. How much do you have to turn it to get the right side in focus? If you have to turn the focus knob counter-clockwise as viewed from the front, I would definately suspect gate parts being worn or sprung. Sooooo......check these things and give us some feedback. Keep us posted. One way or the other, we'll get it solved. Edited for adding more information [ 04-16-2003, 06:09 PM: Message edited by: Paul G. Thompson ]  |  IP: Logged John Westlund Expert Film Handler Posts: 204 From: Burney, CA, USA Registered: Jun 2001 posted 04-17-2003 07:41 PM                     First off I would like to say thank to all of you so far. Sorry its taken so long to get back to you all but here are the results of your suggestions. Questions: 1. Was a magic marker used to "paint the rails" and a loop run through for a few minutes to check the wear pattern on both the shoe and bands? Yes and the outboard side of the trap rail seems to be wearing more then the inboard side 2. Did you check to see if the lens holder is square with the projector casting? Looks to be ok but its hard to tell because I couldnt find a square that would fit in there. 3. Did you install the shoe upside down and run a test loop to see if the focus problem shifted to the other side of the screen? The trap won't close with the shoe installed upside down. 4. Did you "sneak" the film trap open just a slight bit with the projector running and see if the focus change was even across the screen? Yes and the image goes fuzzy across the whole screen. Its hard to tell if its more fuzzy on the right. 5. When the bands were installed, did they properly align with the small dowell pins so they could not cock to one side or the other? The bands are installed properly. 6. What is the positioning orentation of the four screws that holds the light tube (the part that has the trap release knob) with respect to the elongated holes in that assembly? The light tube is installed as far back tward the lamphouse as it can go on both top and bottom. 7. If you focus in the center, how far out oof focus is the sides, and are mis-focused equally? I can get the center and left side to focus evenly and by turning the focus know clockwise i can get both sides to focus pretty close to being the same but the center is now very fuzzy. As for the dovetail. I removed it and it looked ok but just for fun I placed a couple layers of artists tape under the front (closest to the lens barrel) to act as a shim but saw little change. THe lateral guide rollers are fine. The shim under the trap runner showed little change. Thanks Again, John  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-17-2003 07:48 PM                     John, No. 6 could be your problem. It may be jamming the bands too heavily. I suggest positioning the light tube just a little more forward so the trap shoe doesn't smash them so bad. One could be bottoming out. Trial and error will achieve the correct setting. I checked my SA today, and the screws were in the center of the oblong holes in the light tube casting. I had a suspicion that the inboard side would show a little heavier wear than the outboard side. I'll bet the trap was slammed shut too many times through the years, and it sprung the gib, especially with the light tube being as far back as it could go. I talked to Donna today, and she said the focus problem is minor. Nevertheless, it is not perfect. A Century SA should be capable of perfect focus. That is what we are shooting for. However, a possibility does exist the light tube assy is warped just a little, but I doubt it. If there is a problem, more than likely there is a hunk of shit wedged between the light tube bracket and frame, or that surface was painted when the machine was rebuilt. Those surfaces should not be painted. They are machined surfaces. The paint thickness differences even so much as .002 thick can interfere with proper alignment.  |  IP: Logged Dick Prather Master Film Handler Posts: 259 From: Portland, OR, USA Registered: Feb 2002 posted 04-18-2003 03:31 AM                     John, Reference to your #6 & #7 remarks. With the film focus good in the center and off on the edges suggests cuping of the film in the trap. Somethings that cause this are the studio guides too close together, Studio guides grooved, guide roller tension too tight, possible lens assembly too close causing too much tension. One thing to try is moving the inboard studio guide towards the frame to widen the opening for film. You mention the lens assembly being all the way towards the lamp. That may be too close. Set the film trap tension to minium. While running a film you can aford to loose slightly loosten all four screws holding the assembly. Let it set on the screws and move it back and forth slightly until you get the least noise. Make sure the gate is parallel with the trap. Tighten the screws to hold and focus the picture. You only need enough tension to keep the picture from jumping no more. Maybe that will help.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-18-2003 04:43 AM                     If you can get an exact focus on the left side and right side of the screen and the center is out of focus, I agree with Dick. Another thing that might cause that is a mis-focused lamphouse which might be creating a "hot spot" and sucking the film center towards the aperature. However, if the focus drifts across the screen while the focus knob is turned like you orginally suggested, I suspect you still have a warped gib. The slight warp might not be that serious if the film pinching by the guides or being sucked by the lamp is causing most of the trouble. After you get the light tube and the film guides set correctly, you just might be OK. If not, then I would try replacing the gib. I also endorse Dick's method of setting the position of the light tube casting.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 04-18-2003 06:16 AM                        In one of Kodak's screening rooms, we have a pair of Century SA projectors that can achieve a resolution of 80 line pairs per millimetre resolution in the center and 68 line pairs in the corners of test film SMPTE 35-PA (RP40), and less than 1/10 of a square unsteadiness. So with proper adjustment, they are capable of great performance.  |  IP: Logged John Westlund Expert Film Handler Posts: 204 From: Burney, CA, USA Registered: Jun 2001 posted 04-19-2003 02:09 AM                     I gave the machine a good once over today. I adjusted the film guides and followed Dicks method of adjusting the light tube. I also checked the lamp alignment and made some slight changes. After all that the problem was much better but still not gone completely. The focus still drifted across the screen slightly. I then changed the gib with one from a spare SA we have and I think I have fixed the problem completely. Thanks for all your help. John  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 04-19-2003 02:38 AM                     Congratulations, John! You did great! Keep up the good work. Donna needs a person like you in her theatre.  |  IP: Logged

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