Film-Tech Forum ARCHIVE: Odd reflector images on screen

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Posted by Michael Schaffer (Member # 1204) on 02-11-2006, 05:46 PM:

I just went through a location with Kneisley Xenex 2 lamphouse and refocussed all the xenon lamps. The only alignments I found somewhat problematic were one in which the image of the reflector on screen without lens was oval (with the vertical axis being the longer side, like a zero) and another in which it was round, but the hole and lamp were offset about 25% to the left. Obviously, the reflectors themselves are probably not perfectly round and slightly warped, but normally, you don't see them that ungeometrical. The variations I am talking about are far more than what could have been introduced by a slightly unround or warped reflector. Also the reflector in the Xenex lamphouse is sitting in a frame, so it can't just go oval or be at an angle to the filmplane that very different from 90 degrees.

Posted by Richard Fowler (Member # 893) on 02-11-2006, 07:27 PM:

The reflector in the II has some issues with collection of the arc image at certain xenon wattages. I have had to do more ajustments to the system than other lamphouses due to build quality.

Posted by Mark Gulbrandsen (Member # 72) on 02-11-2006, 09:18 PM:

That particuluar reflector works best with short type lamps.

Mark

Posted by Frank Angel (Member # 248) on 02-12-2006, 12:23 AM:

Is my memory playing tricks on me, but wasn't there a design at one time that used a metal reflector which was flexible enough so that for the 1.85 aperture it produced an oval of light so as not to waste a lot of light enregy above an below the aperture rectangle aperture? For scope, the other position allowed the reflector to "relax" and produce a normal, round area of light on the square aperture. Or am I imagining?

Posted by Gordon McLeod (Member # 33) on 02-12-2006, 06:55 AM:

Frank that was the EPRAD Universal lamphouse which performed very well in many installations
We still have several in use up here giving good results

Posted by Michael Schaffer (Member # 1204) on 02-13-2006, 02:40 PM:

quote: Richard Fowler
The reflector in the II has some issues with collection of the arc image at certain xenon wattages. I have had to do more ajustments to the system than other lamphouses due to build quality.

What kind of adjustments?
What I don't quite get is that, even if the reflector has problems collecting the arc image at a given setting, why would the image of the reflector on screen be oval instead of just round, but dim?
You all know what it looks like when you move the lamp in and out of focus, the reflector image expands and contracts around the lamp. But this looks different, like I said, like a zero, like a compressed image in a scope frame (just as a comparison, it has nothing to do with scope, and there is no lens involved here anyway since I am talking about the image of the reflector without lens in the collar).

Posted by John Eickhof (Member # 323) on 02-16-2006, 01:26 PM:

make sure there is no aperture plate in and the film trap door is closed, sometimes there will be vignetting on the film trap door or even a front lens mount..also don't forget the 'focus' knob at the front lower corner of the lamphouse for beam spred!

Posted by Richard Fowler (Member # 893) on 02-16-2006, 03:28 PM:

Busy lately [Smile]

The reflector for some reason tends to give an oval pattern with certain bulbs ( possible design average for the reflector )...reflector shimming, reaiming reflector support and front bulb support with test tools would improve it. Some manufacturers have their signature look [Wink]

I may be mistaken but the man who designed the last model of the Eprad lamphouse I think, did the Xenex II.

Posted by Michael Schaffer (Member # 1204) on 02-16-2006, 05:57 PM:

quote:
make sure there is no aperture plate in and the film trap door is closed, sometimes there will be vignetting on the film trap door or even a front lens mount..also don't forget the 'focus' knob at the front lower corner of the lamphouse for beam spred!

I checked all these things. It is definitely not vignetting since the edges of the reflector are quite well defined and the hole and lamp image in the middle is oval too. They still look quite odd, like this:

quote: Richard Fowler
The reflector for some reason tends to give an oval pattern with certain bulbs ( possible design average for the reflector )...reflector shimming, reaiming reflector support and front bulb support with test tools would improve it.

The lamps were CXL-30R. I have to go back when I have more time and try to align everything with the Align-O-Tron and Kinoton alignment beamer, then see what it looks like. I think one part of the problem, at least for the lower example, might be that the projector head is not centered on the console. Although if the head was laterally off, it should still show you the hole in the middle of the reflector, only that one side might be cut off.