Film-Tech Forum ARCHIVE: The Cause of Strobing

This is topic The Cause of Strobing in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Phil Blake (Member # 2012) on 05-25-2005, 02:39 AM:

Vic 5 consol running 2k xenon , Globe is not far from new.

having an issue when a bright scene is on the screen I am getting bad strobing type flickering , this is worse when the camera shot pans , the bright areas really flicker .

Any ideas On the cause and what the remedy for this is?

Posted by Aaron Sisemore (Member # 145) on 05-25-2005, 03:36 AM:

Run the projector 'wide open' (no film) for a few seconds with the lamp on (being careful not to fry the lens). If you are still getting a slow steady strobing (around 10-12Hz) then you have a bad diode in your power supply, or you have lost one leg of the 3-phase AC power going into the power supply.

-Aaron

Posted by Mike Pennell (Member # 1692) on 05-25-2005, 05:06 AM:

do you mean ghosting? if its only with really bright areas i'd check the shutter timing if its not diode related. check your belts! [beer]

Posted by Randy Stankey (Member # 64) on 05-25-2005, 08:55 AM:

Check your lamp to make sure it's not flickering.

Bad diode in power supply.
Lost phase to power supply. (Or poor connection.)
Old lamp.

Check to be sure your shutter is in time.

You'll probably also see ghosting.

If you don't have your lamp focused properly you might notice some flicker too. Bright spots in the picture can appear to flicker if your lamp produces a hot spot on the screen.
.
Even IF these things are OK, you might notice some flickering in bright scenes if your lamp is too bright. There is ALWAYS flicker in a movie picture. It's just that, when the projector is adjusted properly, most people can't detect it. However, the brigher the picture, the easier it is to detect flicker. In this case, simply turn down the power to the lamp. (Assuming you don't make the picture too dark.)

Posted by Michael Barry (Member # 237) on 05-25-2005, 08:59 AM:

Your shutter gearbox is going/is gone. This is a problem with the Vic 5 specifically.

I had the same problem and we checked the rectifier, xenon, everything...and it turned out to be the gearbox.

If you call Atlab one of their techs should be familiar with the issue - they've changed out a ton of them already.

Michael.

Posted by Mike Blakesley (Member # 26) on 05-25-2005, 12:36 PM:

If you can look in the viewer on the lamphouse and the lamp appears steady, but on the screen (with projector running) it's flickering, then a diode is the problem.

Posted by Rick Long Jr (Member # 541) on 05-25-2005, 06:30 PM:

Try running white light with no film, and partially closing the lamp hand douser just enough to dim the light. Does it still flicker? If so, it's probably a diode/phase issue. If it only seems to flicker with the douser wide open (AKA "shutterbeat") try backing off the lamp focus a bit. Vic 5's and 8's seem to be bad for this kind of thing.

Posted by Stephen Jones (Member # 16) on 05-25-2005, 08:38 PM:

G'day Phil,
Had the same problem with a Vic 5 some time ago.Found that the belt was about to break which was affecting the timing of the shutter,replaced the belt adjusted the timing and problem fixed.As Michael said could also be a sighn that the shutter gearbox is about to [bs]

it's self.As others have said wouldnt hurt to check the rectifier as well as I had problems there to over the years when useing Vic 5 consol units.
Call Atlab in Melb and speak to Bruce or Vince.
Was over West in Feb but esperance was too far from where I was to call in maybe next time.

Steve [beer]

Posted by Phil Blake (Member # 2012) on 05-26-2005, 04:34 AM:

Thanks for all the replys,

Well I ran some white light to the screen. There was some flicker there , but it did not seem to be as much as when the film was running through.

I have checked the shutter timing it was ok , belts are new and the xenon is new.

The shutter box is a concern , the box in the machine is making lots of noise so maybe this is the cause.

The picture is sharp , no ghosting , just flicker and it is worse as I mentioned during bright screnes when the camera is panning.

Posted by Dave Macaulay (Member # 813) on 05-26-2005, 12:36 PM:

You canb check the shuter gearbox by slowly turning the projector by hand and feeling the shutter as it turns, there shouldn't be any jerkiness and the free play in the shutter rotation should be constant through a turn. Make sure the box is well greased, it should be pretty full.
Your flicker sounds like an over-bright image though. Try defocussing the lamp a bit and see if it subsides. Although it would seem that brighter=better, the SMPTE recommended illumination level is a good compromise between image quality and the flicker problem, much more than 16ft-L and flicker gets quite annoying for most people - particularly in moving bright image areas.