Film-Tech Forum ARCHIVE: dark flickering spot

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Posted by Mike Lauber (Member # 1486) on 04-06-2003, 07:06 PM:

I'm using a Strong X60b lamphouse, and a century projector. I am getting a flickering dark spot near the very top center of the screen. The rest of the picture is steady and looks normal. This is the first time I have seen it. It went for the first 15 minutes or so of a showing, then stopped. I know it is about time to change the bulb. Is this problem simply from an old bulb? Or could this have to do with the shutter? Thanks

Mike

Posted by John Westlund (Member # 913) on 04-06-2003, 07:08 PM:

I would think if the problem is the shutter it wouldnt go away. I would assume your problem is somewhere in the lamp. Not much help, sorry.
John

Posted by Bruce Hansen (Member # 281) on 04-06-2003, 07:48 PM:

Could this be nothing more than a piece of dirt that got into the light path, and then was blown away?

Posted by Don Sneed (Member # 955) on 04-06-2003, 07:57 PM:

If your Century's has a fire shutter, it could be a sticking or misadjusted fire shutter...I would also check that !!

Posted by Scott Norwood (Member # 30) on 04-06-2003, 09:04 PM:

If the problem were with the fire shutter or changeover, wouldn't the shadow be visible at the bottom of the picture, rather than the top?

Posted by Paul G. Thompson (Member # 655) on 04-06-2003, 09:08 PM:

The fire shutter drops in from the top. If it was not all the way open, you would see the flicker (fire shutter bounce) at the bottom edge of the screen since there is inversion through the projector lens.

Look down the barrel and see if you can spot anything. (without the lamp lit, of course... [Big Grin]

)

Oops! Scott beat me to that...

Posted by Darryl Spicer (Member # 711) on 04-06-2003, 09:11 PM:

I have to go with the dirt theory. it could have temporarily fallen into a position that got into the light path. Another posability and I have seen this too. Insects can fly and land on the port glass. Large enough it can block some of the light.

Posted by John Westlund (Member # 913) on 04-06-2003, 09:43 PM:

I have had to go attepmt to remove a bug from the port glass a couple times. I saw just about the same effect as was described in the original post.

Posted by Michael Schaffer (Member # 1204) on 04-07-2003, 01:58 PM:

Could it be the shadow of the cable from the anode?

Posted by Adam Martin (Member # 641) on 04-07-2003, 02:12 PM:

What kind of hand dowser does this lamphouse have? I'm too lazy to look it up. If it opens down like a Super LumeX, the hand dowser may not have been open all the way and eventually vibrated itself into position.

What did the spot look like? Did it go all the way across the top of the screen or was it just a few feet wide on the screen?

Posted by Mike Lauber (Member # 1486) on 04-07-2003, 04:07 PM:

The spot was just a few feet wide, and it only came down a few feet from the top. It was not the fire shutter, I checked that. I do have a feeling it must have been simply a piece of dirt or dust that was blown away. The lamp is getting old in there, but this spot was in dark contrast to the rest of the screen, so I don't believe it could have been a lamp problem.

Mike

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-07-2003, 04:48 PM:

Might have been a splicing tape chad (little square) stuck to your aperture plate. Do you make sure that all the chads are/have been removed from the film when you make splices?

If you've got a really big screen the little square can appear quite large.

In all likely hood, though, it sounds like you just might have forgotten to clean your aperture plate before the show.

Posted by Josh Jones (Member # 447) on 04-09-2003, 06:59 PM:

Considering the nature of the plastic used to make the tape and the intense heat at the aperature, the tape piece would have melted within a few seconds. If there was dirt in there, especially oily dirt, it will smoke. When I first fire up my machines after they have sat idle for a while, some parts of the aperature start smoking because the oil needs to be burned off.

Josh

Posted by Daryl C. W. O'Shea (Member # 1303) on 04-09-2003, 08:51 PM:

I have actually seen pieces of splicing tape caught on an aperture that have cast shadows on the screen. Regardless, it was probably dirt that caused the shadow in this case.

Posted by Frank Angel (Member # 248) on 04-10-2003, 03:35 AM:

Bugs? You wanna see BUGS? We are gearing up for Movies in the Park and there is no end to the bugs I get out there. That booth has an open front and bugs....big, SCAREY, MUTANT bugs fly all over the booth and of course, try to commit suicide by flying right into the lens where the heat of the projected image usually does them in, but not before they make a fluttering shadow on the screen. The thing is, they start their flight to the projected light way out in the field. As they get closer and closer, the shadows get bigger and bigger; they can really make some distracting (and disturbing) shadows on the screen. I've taken to buring OFF's Anti-Flying Insect wicks in all four corners of the booth (in their ceramic cases for safety) and I keep a can of compressed air so I can blow them out of the lens if they don't die before they get in the barrel. The buring wick seemed to help a bit last season, but it certainly doesn't eliminate all of them.

In the indoor booth I can still get the occasional fly the size of a Buick that slams itself against the port glass for hours if you don't deal with it. Only solution I found for that was to put fly paper down on the perimeter of the ports, in the hopes that the little freak will get his ass stuck on it. That seems to work pretty well, but it's a messy proposition and they still can get at the light beam if they dive in head first.

Frank

Posted by Bruce Hansen (Member # 281) on 04-10-2003, 06:59 PM:

Frank,

Just a suggestion that might help with keeping the bugs from getting real close to the lens. Use one of those home "box" fans beside the lens, to blow them away.