Film-Tech Forum ARCHIVE: 4KW Xenex 1 - Produces a Halo on the screen

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Posted by Barry Floyd (Member # 385) on 07-17-2006, 02:53 AM:

We just replaced our older Christie 4K lamphouse with a 4k Xenex 1, and when the bulb focus is brought in tight enough to produce acceptable light levels on the screen we end up with this weird "Halo" effect in the center of the screen. The flat lens produces a round halo, while the scope lens produces an eliptical halo.

When we first bought the Xenex 1, it was shipped from the dealer with a "bulb bushing" for a 2k lamp instead of the bushing for the 4k, and the lamp adjustments could not move the lamp back far enough into the reflector to project a bright enough picture on the screen. Our Tech came out and moved the bushing BEHIND the reflector which allowed the lamp to move back into the reflector, and temporarily shimed it in place until the new bushing arrived. The picture looked great.
When the new bushing arrived, Kneisley sent the wrong one, but the tech (in his efforts to get us on the screen)had the replacement bushing "machined out" to fit the end of the bulb.
While he was there on the last trip, he also jacked up the amperage from 120 to a little over 140 amps.

Here's the equipment I'm dealing with:
Lamphouse: Xenex 1 with the Glass reflector
Lamp: NEW 4kw Osram
Projector: Brenkert BX-60
Lenses: Flat - ISCO / Scope - Schnieder backup lens with an ISCO 1/2 REVERSE Anamorphic.

My thoughts are that the bulb may actually be running too bright. If I crank down the lamp focus to tight, I get the Halo effect, if I back it off, the halo goes away - but the picture on screen gets unacceptably dimmer. If we drop the amperage back down to the 120-130 level, then tighten up the focus on the lamp - would that make the halos go away??

Thoughts anyone??

Posted by Monte L Fullmer (Member # 2797) on 07-17-2006, 05:05 AM:

Maybe some small thoughts to begin with: what does the light look on the screen without any lens - just shooting the light through the machine and doing your rough focus (the "Looney Tunes" rings) on the screen - to center the bulb to the mirror?

Was the Xenex I string aligned to the projector?

Have to eliminate the lens since the halo effect seems to be for both-not just one since the description of round and elliptical halos are results.

I'd say it's a bulb to mirror to projector alignment issue.

good luck-Monte

Posted by Mark Gulbrandsen (Member # 72) on 07-17-2006, 06:16 AM:

quote: Monte L Fullmer
Was the Xenex I string aligned to the projector?

Monte.... The string alignment method died with Thomas Edison... The best way to align lamphouse to projector is with the Kinoton alignment tool, or with the Alignotron... The Kinoton works the best for mirror to lens mount since it is a true 3D alignment tool. The alignotron is alot more limited in its use but can be used to check both ends of the bulb mounts to be sure thay are also in the proper plane after setting the mirror with the Kinoton device. Be aware of the alignotron as two that I've seen do not project a straight path(try rotating one when its on) and the laser diode also needs to have an aperature in front of it so it projects a round spot.

Barry,

I thing we need more info as to your projector and lenses but it soulds like an alignment problem to me... either lamphouse to projector or the bulb position inside the lamphouse is still off. Wait till you get some hours on your lamps and have a hard time igniting the lamp when it is still warm.... thats always been a problem with the Xenex-1. Best to leave it on between shows on really busy nights!

You'd have been better off keeping the Christies and getting the retrofit kit from Technilight. Those retrofits really work very well. We have a 6 screen D.I. in SLC that retrofitted all 6 of their 4kw Christies and they now have light levels that rival any good indoor theater.

Mark

Posted by Richard Fowler (Member # 893) on 07-17-2006, 08:48 AM:

Beside alinement, check the adjustment on your arc magnet. The Xenex I works well in medium and long throw situations.

Posted by Barry Floyd (Member # 385) on 07-17-2006, 09:03 AM:

Mark,
Our old Christie lamphouse literally went up in smoke about a month ago. My wife was leaving the theatre one night and shut off all of the exhaust fans and projectors, but did not turn off the lamp in booth #2. It literally ran until it fried itself. I came in the next night and found small puddles of solder inside the bottom of the lamphouse cabinet.

Our tech did use one of those lens barrel lasers to check the alignment on the bulb. When I saw it, the red dot from the laser was shining on the end of the tip of the bulb.

Looks like I need to get my tech back out to re-align the machine.

Posted by John Pytlak (Member # 331) on 07-17-2006, 10:09 AM:

If you are getting a halo or doughnut pattern light distribution on the screen, but the "halo" is more or less centered, you should check the mirror-to-aperture distance to be sure it is in specification, and then the lamp focus. Adjust lamp focus for the optimum uniformity and light level, without "hot spotting", which could damage the film.

Posted by Louis Bornwasser (Member # 3063) on 07-17-2006, 04:21 PM:

Light is always a problem in a drive in. Rethink the optics in a Xenex I and a Brenkert. Brenkert is about F2,4; the Xenex I was F1.7 according to Dick Kneisley.

I guess what I am saying is that A LOT of light is not making it to your lens. Louis

Posted by Mark Gulbrandsen (Member # 72) on 07-17-2006, 05:15 PM:

Hopefully he has a drive in blade on the thing. The drive in near Powell, WY has a BX-60 and a really decent picture running with a Strong to kneisley xenon conversion kit in it.

Mark

Posted by Barry Floyd (Member # 385) on 07-18-2006, 02:33 AM:

My tech is coming out on Tuesday night to see what he can do. Tonight before the shows started, I popped open the side of the lamphouse to take a look to see if I could figure anything out.

Here's what I think COULD be part of the problem.

The round teflon bushing that goes thru the reflector to support the bulb is white in color and has about a 1/8" flange around the neck of it to keep it from sliding thru the rear of the reflector. Is it possible that as the bulb is moving back into the reflector, the bright white light from the lamp is intensley illuminating the flange of the bushing and being reflected back out of lamp??

I thought about removing the bushing, painting it with a flat black high-heat paint and seeing if that would help correct the problem.

Posted by John Pytlak (Member # 331) on 07-18-2006, 08:16 AM:

I don't think it is a reflection from the bushing. I've seen "halo" or "doughnut" light distribution on some lamps when the lamp focus has not been set properly.

Posted by Richard Fowler (Member # 893) on 07-18-2006, 09:43 AM:

The bushing is "out of focus" in regards to the reflector and the arc flame so bushing color is of no concern. The reflector distance from rear of reflector to film plane should be 28 inches / 711.2 mm.

Posted by Gordon McLeod (Member # 33) on 07-18-2006, 11:50 AM:

What type of projection lens do you have
The Xenex1 has been known to have issues with some lens producing weird focus issues as well
I suspect that the lamp is probably not sitting in the reflectors focus point due to the bushing

Posted by Brad Allen (Member # 470) on 07-18-2006, 01:48 PM:

quote: Barry Floyd
Our old Christie lamphouse literally went up in smoke about a month ago. My wife was leaving the theatre one night and shut off all of the exhaust fans and projectors, but did not turn off the lamp in booth #2. It literally ran until it fried itself.

Barry, that's why it is very important to wire the exhaust blowers in such a way that they run anytime the lamphouse is on and can't be shut off, unless the lamphouse is off. Also use Brad's timed relay trick that keeps the exhaust blowers running for a predetermined amount of time after the lamphouse shuts off. This takes the human element out of the loop and the possiblilty the blowers not running long enough for cool down.
$35-$40 worth of relay's and some simple wiring is all it takes. Grainger sells the timed relays.
I would of thought your tech would of installed them this way. [Eek!]

Posted by Barry Floyd (Member # 385) on 07-19-2006, 09:12 AM:

Problem solved... The new bulb was WAY out of focus. Our tech spent 15 minutes in the booth and he was gone. The picture now looks fantastic.

Thanks for everyone's help and suggestions.

Posted by Chris Erwin (Member # 176) on 07-19-2006, 12:16 PM:

Barry,

Did someone bypass the airvane switch in your Christie or did it fail?

All,
I thought you couldn't run the lamp unless you had positive airflow on the lamphouse...A safety feature so it wouldn't nuke out or kill the bulb.

Although I do know some people that "jinksies" things to get 'em going and then don't undo their handiwork causing said problems. (i.e. this lamphouse keeps eating bulbs, the exhaust fan ran only intermittently and no one figured it out till someone got in the 'inerds and discovered the bypass then the ailing fan motor)

The Xenex is a good lamphouse. A similar one is cranking out 3k at Judy! I wish you the continued best on both screens!

Posted by John Pytlak (Member # 331) on 07-19-2006, 12:23 PM:

quote: Barry Floyd
Problem solved... The new bulb was WAY out of focus. Our tech spent 15 minutes in the booth and he was gone. The picture now looks fantastic.

Glad we were able help! [thumbsup]