Film-Tech Forum ARCHIVE: XENON 7K lamp alignment problems

This is topic XENON 7K lamp alignment problems in forum Large Format Forum at Film-Tech Forum ARCHIVE.

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Posted by Ivan Plamondon (Member # 7637) on 08-09-2013, 05:18 PM:

During my last two lamp changes, I have noticed a "hot Spot" located in the lower center of the screen when running the test loop(and viewing our feature film). No amount adjustment to the x, y or z axis can move this hot spot to the center of the screen. I have spoken with our IMAX tech and he says I basically have to live with this current scenario. Does anyone have any suggestions as to why this is happening?

Posted by Richard Hamilton (Member # 321) on 08-10-2013, 06:00 AM:

sounds like your IMAX "tech" is lazy [Roll Eyes]

Posted by Dave Macaulay (Member # 813) on 08-10-2013, 09:43 AM:

What kind of projector though? Is this the Niagara Falls theatre?
I think NF has the Imax "Classic" with a 7kW aircooled lamphouse, as I recall that type has no folding mirror (been a while, I could be mistaken).
Either the reflector is distorted or the reflector optical axis is not coaxial with the lens optical axis. Neither was unusual with the 7kW lamphouse.
I think the reflector had to be cut to fit and the cutting could distort the shape, but it can be checked with a point source light (like a krypton 2AA mini maglight with the front cap off, poked through the reflector hole from the back) - the light pattern projected from the mirror onto a wall contains a bunch of concentric circles which will be round from a good reflector, odd shaped if the shape is distorted.
Alignment of the axes was done with either a string (old school, not very accurate) or with a laser mounted in the reflector hole with its beam on the reflector axis, the mirror is moved so the beam is down the centre of the lens axis (the reflected light pattern from the lens elements then becomes concentric circles, one for each element).

Posted by Ivan Plamondon (Member # 7637) on 08-10-2013, 04:34 PM:

I'm hoping it gets resolved at my next service this month. It's been a challenge finding a midway point between reducing the "hot spot's" brightness by pulling back on the "Z" axis vs keeping the overall image as bright as possible by increasing the rectifier's power.We currently try to hover around 155 amps and 32 DC volts in order to attain longevity with our lamp (700 + hours). The last few weeks of the lamp life, the amps usually drop to around 150. I'm the "new kid on the block" here so I'm trying to get as much knowledge as possible. Thanks everyone for your input on this matter.

Posted by Gordon McLeod (Member # 33) on 08-17-2013, 03:03 PM:

Pyramid Place Imax remember it well
It had a classic aircooled machine the reflector came from ORC if memory serves

Posted by Ivan Plamondon (Member # 7637) on 08-17-2013, 07:43 PM:

Can't wait for our next service call. Laser alignment is in the works!

Posted by Ivan Plamondon (Member # 7637) on 08-26-2013, 09:15 PM:

Turns out the mirrors were out of alignment. Balance has been restored thanks to our service tech.