Film-Tech Forum ARCHIVE: Ballantyne flicker

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Posted by Scott Balko (Member # 438) on 05-19-2001, 10:48 PM:

My Pro 35's have a shutter flicker that is somewhat annoying. I figured that with the short throw of my screening room that a 2000 watt lamp may be the culprit. When I de-focused the lamp, it was considerably better, but it was still there. I timed the shutter just to be sure that wasn't it and I noticed that there was a considerable amount of time that the shutter was completely blocking the aperture before and after the intermittent movement. Could the shutter be taylored to block the light immediately before int. motion and then to open immediately after? Would trimming the secondary shutter gate (the one that is on the other side. I don't know what to call it

) be advisable if the shutter was rebalanced afterward, or wouldn't that even make a difference?

Maybe I should ask if I'm even digging in the right place. My lamp isn't the source of the flicker. I already checked. It is definitely shutter oriented. Any suggestions would be great!!

Posted by Jerry Chase (Member # 660) on 05-20-2001, 12:58 AM:

I think you can change the machine to a three bladed shutter.

Posted by Paul G. Thompson (Member # 655) on 05-20-2001, 02:09 AM:

Scott, it still sounds like the shutter timing is still off. Time it exactly as the book says. Unfortunately, you might have to do it several times until you get it right. They can be very touchy...

If the ghosting was in both directions, you might have a drive-in shutter on that machine. If so, replace it with a standard indoor shutter.

Posted by John Pytlak (Member # 331) on 05-20-2001, 06:50 AM:

"Flicker" usually has nothing to do with the shutter timing. Excessive screen luminance makes shutter flicker more visible, so be sure the screen luminance does not exceed the 12-22 footlambert range allowed by SMPTE 196M. To virtually eliminate shutter flicker, use a 3-blade shutter to raise the interruption rate from 48 cycles to 72 cycles. But a 3-blade shutter is only half as efficient as a 2-blade shutter, so you will need twice the lamp power to maintain the same light level.

Many studio and lab screening rooms use 3-blade shutters because they want to completely eliminate flicker, and the relatively small screens don't require very high light output to maintain the aim of 16 footlamberts. A home screening room likewise is a good place to use 3 blades. Large screens need lots more light, so 3-blades are impractical for very large screens.

Sometimes, even if there is no visible flicker without the shutter running, and an annoying 12 Hz flicker when running, the problem is AC ripple in the lamp power supply. The 48 or 72 cycles of the shutter "beat" with the 60 Hz. AC ripple component, showing up as a 12 cycle flicker.

If you have TRAVEL GHOST, then check the shutter timing.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Scott Balko (Member # 438) on 05-20-2001, 09:36 AM:

The three blade shutter sounds like the ticket. I've got plenty of lamp for it. So how do I go about getting one, two in my case. Change-overs you know.

Posted by Gordon McLeod (Member # 33) on 05-20-2001, 09:42 AM:

How big is your screen? a 2K lamphouse (especially if it is efficient) is for a 28' approx. screen size.
You probably have 2 much light
Use the SMPTE 35PA test film and look fopr travel ghost in the black blocks.
If it is a screening room a 3 blade shutter is advisable. I don't think there is one for the pro35 nor do I believe they made a drivein shutter for it

Posted by Paul G. Thompson (Member # 655) on 05-20-2001, 02:48 PM:

Scott,

Was it a flicker or a ghosting problem? For some reason I thought it was a travel ghost problem.

Posted by Rick Long (Member # 213) on 05-21-2001, 12:05 AM:

Gonna assume that you projected light without the projector running (shutter blade out of the way, and the change-over blade held open with a coat-hanger). It the light appears steady, the bulb is probably not at fault.

Now, if when the projector is running, you obseve noticeable flicker, I would think it is probably the result of the 48 Hertz exposure from the projector, "beating" with the 60 Hertz ripple from the rectifier. This would likely be caused by a failing filter capacitor in the rectifier. It can be proved by parallelling the existing capacitors with another unit of the same size (micro-fard (uuf) and votage rating).

As has been mentioned, in a rectifier that passes spec, "shutter beat" can be noticed if the screen illumination is excessive.

Posted by Paul G. Thompson (Member # 655) on 05-21-2001, 12:31 AM:

Scott, we still don't have all the information. It was not indicated what voltage and current the lamp is being operated with.

Rick and John, in addition to what you gents said, there is a possibility of a bad diode in Scott's power supply. But nobody knows yet with the info we have, because nobody hinted about the current and voltage at the lamp. It could be the 12hz strobe he is seeing. We'll just have to wait and see until Scott gives us more information.

I never had the problem like Scott's when using a 2000 watt lamp on a Pro-35....But yes, Gordon may be correct when he said "too much light".

I believe Gordon is also correct about the availability of a three wing shutter or a drive-in shutter. Unfortunately, some theaters have the local machine shop "butcher" the shutter and re-balance it for a drive-in application.

After reading Scott's original post on the way the shutter is positioned before and after pull-down, he either has too much light on the screen - or there is a ripple problem due to bad filtering or a blown diode. But here again, I don't know if his problem is on just one or both machines, and when it started.

It is possible that if he throttles his bulb back a little, his problem might go away if it is just "too much light", or use a 1600 watt lamp.

Posted by Brad Miller (Member # 2) on 05-21-2001, 04:13 AM:

If it is a bad diode, viewing the light on the screen without the projector running can be deceiving and give the impression of a flickerless light source. Always have the projector running. Since you have two projectors and did not make a notation about only one machine having the flicker, I will assume that both do and the odds of a diode being bad in both rectifiers is very slim.

Hold one of the lenses of a pair of sunglasses in front of the lens and see if the flicker is still there. If it is, you have a bad diode. If it goes away, you need to get that 3 bladed shutter, run with a lower wattage lamp or defocus the bulb. You might also want to consider using some heat filters as well to cut down on the amount of light transmitted to the film (as well as to reduce the heat on the film).

Posted by Rick Long Jr (Member # 541) on 05-21-2001, 03:10 PM:

An old projectionist once told me that a flat black shutter blade produces less flicker than a plain metal blade. He had removed all of the blades from his Amateur 35's and sprayed them black. I have never had the opportunity to try this myself and fortunately we have uninstalled almost all Ballantyne projectors in this area. I know most Century and older Cinemeccanica blades were black. Any one else ever heard of this?

Posted by Scott Balko (Member # 438) on 05-21-2001, 06:46 PM:

Sorry I haven't been able to give you all the information you need. Film is just a hobby for me and my job (not film related) takes most of my time on weekdays.

First off, I wasn't referring to a ghosting problem. I hope I didn't confuse anyone. My problem is definitely a shutter flicker. If I leave the light on through the aperture and shut the motor off, the flicker follows the speed of the shutter to a tee.

I know that I definitely need to put in smaller lamps for one thing as my power supplies are only rated for 1600 watts. They have been modified with the cooling fans for higher continuous output, but it simply isn't enough.

I'm also still in the setup mode, so I haven't been able to do a direct side by side comparison. The one thing I did notice, however, is that the power supply I've been refering to won't hold a steady amp or voltage reading. The amperage will drop slightly and at the exact time the voltage will increase slightly. The other lamp/power supply combination was rock steady. From this sketchy description, is it possible to determine if the problem is in the lamphouse or the power supply? My next step was going to be to switch the power supplies and see if that changes anything.

Will a 1500-1600 watt lamp go directly in place of the 2000? If so, anyone wanna trade?

BTW, I liked the comment about the "Amature 35".

Posted by Gordon McLeod (Member # 33) on 05-21-2001, 07:20 PM:

Lamp interchangablity depends a lot on the make of lamphouse and rectifiers
also how big is the screen

Posted by John Pytlak (Member # 331) on 05-21-2001, 08:06 PM:

Rick:

A black or anodized shutter blade will absorb the energy, rather than reflecting it back to the lamphouse. So although there will be less stray light bouncing around to deal with, it may run hotter (and be more prone to warp or be damaged by the radiant energy). I don't think it will affect timing and travel ghost, unless there is so much stray light bouncing around that the film is somewhat illuminated during pulldown.

Posted by Greg Pauley (Member # 503) on 05-21-2001, 10:13 PM:

In addition to all the previous posts, if you are unable to time the shutter on a Pro35 you might want to inspect the fiber gear located on the end of the shutter train were it contacts the vertical shaft. I have seen where a small chunk of the fiber gear will break off causing a shutter ghost but still rotating the shutter. Turn the shutter blade over by hand and see if you feel a dead spot in the rotation of the shutter blade.

Posted by Paul G. Thompson (Member # 655) on 05-21-2001, 11:34 PM:

Well, I now presume it is happening on both machines, and I presume the lamp currents and voltages are correct. I also presume there is no 12hz flicker.

Throttle back on the lamp, or go to a smaller xenon bulb.

Also, operating the rectifier outside the parameters (especially over maximum rating) is not a cool idea - no matter how much cooling you provide. The filter capacitors will not adequately filter the AC component out of the DC.

Posted by Gordon McLeod (Member # 33) on 05-22-2001, 10:08 AM:

In many screening room where they have too much light we insert a piece of stainless steel screen material between the lamphouse and the trap.
In fact we mounted them in a empty heatfilter holder

Posted by Bruce Hansen (Member # 281) on 05-22-2001, 05:10 PM:

I notice that you said at time the current goes down and the voltage goes up. This indicates a change in the load on the power supply. Check to see if you have any loose or dirty connections. I agree that the filter caps. are not sized to handle the increased current for the 2K lamp.

Posted by Scott Balko (Member # 438) on 05-23-2001, 05:10 PM:

Yep, it happens exactly the same with both projectors. However, my other power supply has a very constant reading on the amp and voltage meters. That tells me that I've got problems in my power supply, correct?

Anyhow, you guys have been a wealth of information. I thank each one of you for your input. I'm having some 3 blade shutters made, so hopefully that will take care of the flicker.

Anybody want to trade some 1600 watt bulbs for a pair of 2000's. The bulb is very clear except for one little spot by the fill knob. Anybody have a pair of 1500-1600 watt bulbs for sale?

Posted by Paul G. Thompson (Member # 655) on 12-06-2002, 03:22 PM:

Now I have also noted a problem similar. I am running a Simplex XL (has a black shutter) and the theatre has a 41-foot throw, very large screen. I have this flicker on another also. But it is not quite as bad. It is more noticable in only one house. The third house (which is actually House No. 1) has about the same size screen, but there is no flicker. The light on all three screen meets (but does not exceed) SMPTE standards. All three setups have Super Lumex lamps, with 3,000 watt Strong Switchers. I am running identical currents (90 amps) on the 2500 watt Christie CH-25 lamps. All three Simplex XL's are identical, equipped with straight gates.

Shutter timing is perfect, and flicker I discribe is not a srobe flicker like you would expect to see if a diode failed in a reactance power supply. The flicker does not really appear to be a picture jitter, as the registration of the picture on the screen is steady.

With the projector stopped, shutter open, CO open, and lens removed reveals absolutely no flicker. Insertion of the lens, running the projector with no film, the small amount of flicker you would expect to see is very normal.

With film running, the flicker appears to be at a 24Hz rate.

Lamp focus is normal, with a flat field.

I wonder if I have a Switcher problem, or a gate problem. I have not swapped gates around with the machine that does not flicker. Not yet, anyway...

Help - any other suggestions? I have this feeling swapping gates around is not going to solve the problem. Is there a possibility it could be a switcher problem that will show up more noticable with film running in the projector?

Posted by Jack Ondracek (Member # 1466) on 12-06-2002, 05:34 PM:

Paul, I haven't experienced much trouble with switchers. However, at the frequencies they run at, I wonder where in the circuitry you'd get a frequency that would cause any noticeable variation through the bulb. Considering the components are all designed for the high freq operation, I'd think something that noticeable would also be heating things up pretty well in the supply... if it was possible at all. Doesn't the transformer in there run off of the high-freq voltage? It probably wouldn't be very efficient if something were to lower the oscillator, and you'd probably see that in lousy current, if it'd work at all.

(Hope I didn't put my foot in it... but I don't see how the switcher could be doing anything you wouldn't see on the ammeter).

Past that, it'll be interesting to hear what you find. It sounds like you've covered it all.

Can screen-type push something like this over the edge? If you're close to overlamping, would a screen with too much gain highlight a problem that might not be noticed in another room?

Posted by Pat Moore (Member # 380) on 12-06-2002, 06:32 PM:

Some good comments above, but it seems like we need some definitions cleared up and a better description of the problem. I think Gordon is highlighting the most important question -- how much light is actually on screen? Is the complaint actually "flicker" or something else?

Flicker is probably best defined as a pulsation of the light level on screen that's noticeable or objectionable. Experience tells us the primary cause is excessive AC Ripple in the DC Current to the lamp, normally caused by an open or shorted diode or other rectification / filter problem in the power supply. Flicker would be evident on the entire screen and is quite different from "arc waver", another light sourced based problem visible on screen. Arc waver is movement of the DC arc or plasma ball in the lamp that actually creates a moving light pattern on screen.

A projector's effect on flicker from the shutter (a 48HZ pulse) is visible at high light levels on a white light screen. Depending on the projector's optical characteristics, shutter flicker becomes objectionable somewhere above 18-22 foot-Lamberts. However, the effect could be invisible still depending on the film being shown and its density. That's why SMPTE has minimum and maximum light levels as standards.

On the surface, this problem sounds like too much light on screen. The Ballantyne is a very efficient projector light wise and unless there is ghosting, I don't think the problem is in the head, assuming all else is normal.

Pat

Posted by Paul G. Thompson (Member # 655) on 12-06-2002, 06:57 PM:

Pat, it looks like a "Flicker Flutter" - (Now that's a mouthful)

I wish I could describe it better. I might have a gate problem in conjunction with what I thought might have been a power supply problem. I have never seen this particular problem before in my 35 years in the booth. I am going to swap gates tomorrow, and I will report back as to whether it got better, got worse, or went away.

I might add this: Seems lile it is worse at startup of the movie. At the end credits, the problem seems to be gone.

Posted by Paul G. Thompson (Member # 655) on 12-07-2002, 04:10 PM:

It is definately a gate problem. I have a picture jitter of 24hz, and a focus flutter to boot. These machines rebuilt under 2 years ago, but the guides and other crtitical gate parts were not replaced. A bunch of new parts and some major readjustments should correct the problem. I did note one of the intermittent movements is also out of adjustment, and backing off on the lamp focus has definately helped reduced the jitter and flutter, but it is still there.