Film-Tech Forum ARCHIVE: Focusing a Xenex lamphouse

This is topic Focusing a Xenex lamphouse in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by David E. Nedrow (Member # 4981) on 10-10-2012, 01:37 PM:

To get our second projector back up, I scrounged a Xenex lamp house. This is a straight Xenex, not a Xenex II.

I'm baffled as to how to focus the bulb. It appears as though the carriage to which the bulb is clamped is designed to move forward and back. There is what appears to be a threaded screw hole in the bulb-side edge. There are external control for tilting the mirror, but nothing for focus.

Should I move the carriage to focus? With the bulb on?! I'm not sure how else to do it without making a hundred tiny moves with the bulb dark, turning it on, turning it back off, move the carriage, etc.

-David

Posted by Dominic Espinosa (Member # 2122) on 10-10-2012, 02:32 PM:

Can you take a picture of the rear of the lamphouse for us?
IIRC on these there should be a screw for focus and 2 knobs for vertical/horizontal.

Posted by Monte L Fullmer (Member # 2797) on 10-10-2012, 08:35 PM:

Like this XENEX at a local drive-in ...

A plain Kneisley XENEX, when you look inside, almost looks like a carbon arc retrofit with using the same glass reflector as a Peerless Magnarc.

to focus the bulb: Front of the lamphouse and below the "snood" (should be) is that black knob that pulls the bulb's front mount assembly back and forth for focus.

Looks like you've got easy controls for the X and Y axis adjustments.

Now, where you don't have a knob, do your best to use whatever tool to rotate the screw so the carriage can slide back and forth for focus.

Now, here's the gimpy swing of it all: Lamphouse was designed to use OSRAM bulbs only due to the cathode seal end of the OSRAM bulb DOES NOT have a front shoulder so the cathode seal end can slide THROUGH the reflector's insulator ring.

If that bulb has the lamphouse mounting assembly ring mounted too far back on the anode seal and you put it in the lamphouse, then you do the focus, the raised shoulder on the bulb will not allow the bulb to retract through the reflector when you turn that black knob on the lower front of the lamphouse.

The bulb has to expand when operating and passing though the reflector allows the expansion. If the expansion is not allowed when the cathode end jammed against the reflector seal, bulb explosion becomes possible and loss of reflector along with it.

(and ask me about changing out the igniter in that lamphouse...bit of fun to do, esp if you have an autostrike board in there..)

Good luck - Monte

Posted by David E. Nedrow (Member # 4981) on 10-10-2012, 09:27 PM:

Monte, that's it exactly. How I missed the giant black knob, I'll never know. [Wink]

And thanks for the pointer on the shoulder/mirror retraction.

-David

Posted by Gordon McLeod (Member # 33) on 10-15-2012, 10:24 AM:

the reflector was not a magna-arc reflector completely differemt spec

Posted by Monte L Fullmer (Member # 2797) on 10-16-2012, 02:16 AM:

True, different spec, but looks similar (should have said "similar to a Magnarc lamphouse reflector" ..).. my error.

Posted by Sam D. Chavez (Member # 1841) on 10-16-2012, 09:35 AM:

Picky, picky.

Some of us knew what you meant Monte.

Posted by Tony Bandiera Jr (Member # 2365) on 10-16-2012, 12:17 PM:

I knew what he meant. Gordon is just a pedant. [Big Grin]