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Topic: Funny light artifact

Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 04-21-2000 08:46 AM

I have a problem that I'm sure is an aiming problem of the lamphouse (Super Lume-X) I have this large arc of light that is only visible during a dark (black) scene. It extends from the lower left corner to the upper right corner. I think I can fix it with aiming adjustments, but I don't have any dark film to make a loop out of. What I need is black, but not opaque, film about 25' worth. Anybody got a suggestion?

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 04-21-2000 08:48 AM

Yea, order a short length od Schneider lens resolution test film. Its black with resolution markings in white. Its a tough film to project and an even tougher test on a lens.
What kind of projector are you setting this up with? This shouldn't be too hard to set up.
Mark

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-21-2000 10:33 AM

Is there a gab between the front of the lamphouse snood and the proj head that the light is leaking out
The alignment whould be done with the string kit then look for the leak

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-21-2000 10:35 AM

Stop the presses
I believe you have a Norleco AA2 (dp70)
They sometimes get a light leek in the front because of the large opening in the front casting but with a small lens set back in the holder
Cut out some cardboard to make a donut arount the front of the lens bushing

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 04-21-2000 10:56 AM

How about just making a loop using the dark "run-out" on the head/tail of a trailer or print?

I'm guessing but, are you sure it's something that's comming through the lens? I'm sure you've looked at the screen with the dowser closed, but what if you put in a blank aperture plate? Or, block the light around the projector port, except for a cutout exactly the size of the light beam. Could light be sneaking out somewhere else and, say, going out the viewing port? Is there an exit sign with it's cover open nearby, or some other light source?

The reason I make these suggestions is that I never saw that kind of problem with a mis-aligned lamphouse; other light problems, yes- but not a streak of light. Did this just happen, or did you just install the lamp?

If you're sure it's comming out the lens, I would check that: the reflector is not stained or damaged; the lens is not cracked; something like the dowser or zipper shutter is not hanging down too far, or the paint got scraped/burned off of the regular shutter- reflecting light back to the reflector.)

Put light on the screen with the projector running, but no lens installed. The rings should be concentric and centered in the screen rectangle, with a dark blob in the center. If so, then the lamp is aligned (maybe not perfectly, but) enough not to have this problem. I don't think adjusting the XYZ settings will fix this, unless something else is wrong, and changing the aiming corrects for another problem.

My own 0.02 worth, which is probably worth less.....

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 04-21-2000 04:26 PM

It's a DP70 projector. I just put the Lume-X on it (nice improvement on light) I did the string alignment thing, and it look right on. I'm hoping it's not some kind of lens reflection into the lamp reflector. At first I thought it was the exciter lamp shinning throungh the gaps. (This is a small screening room 27' throw 6x14' screen) I'll try the cardboard shield idea. If I move the rear of the lamphouse to the left will the arc on the screen go to the right or left? (I guess I'll see) Any guesses?

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 04-21-2000 08:23 PM

Is it a lumex or super lumex?
The excitor lamp also is norotius for leeking out
At OP before the Jax Light I had to hang a business card under the lens mount because in a dark scene on a 80' screen there was a funny light link that would go away with the excitor off

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 04-21-2000 10:37 PM

Yes, I forgot about the exciter lamp light shinning out (on a AA-II.) We fixed ours with a very small card in just the right place. The lens would reverse everything, so moving the lamp left should make the light go right.

Wow, Gordon- you've got a good memory!

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 04-21-2000 10:53 PM

It's a Super Lume-X

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Pat Moore
Master Film Handler

Posts: 363

Registered: Mar 2000

posted 04-22-2000 09:05 AM

I think Gordon is on the right track with this, I think it's a light leak around the lens holder. Should be pretty easy to find. Just hold a sheet of paper around the front of the projector, but not in the light path from the lens. The artifact should show up pretty easily.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 04-25-2000 07:35 AM

Greg:

A good way to track the source of any stray light is to cast a shadow in the lighted area, which will point to the source of light. The method was discussed in my article on "Conquering Contrast Killers" in Kodak's December 1999 "Film Notes for Reel People":
http://www.kodak.com/US/en/motion/newsletters/reel/december99/pytlak.shtml

I have seen cases where a reflection off a shiny component like the freshly filed edge of an aperture plate can cause a light streak on the screen. Lamphouse alignment can affect these stray reflections.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 04-25-2000 07:53 AM

I just got a 100' roll of dark film and will make up some loops and then start the search. It's barely noticable (except to me) but I want it gone. Thanks to all for suggestions

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