Film-Tech Forum ARCHIVE: Chronic dimness

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Posted by Dominic Espinosa (Member # 2122) on 08-09-2011, 04:01 AM:

Hey guys,
Searched dim OR dark a bit ago but didn't turn up anything really conclusive...

I've got 2 35mm houses reading about the same light level.

The first is a 2k lamp in an LP Associates lamphouse behind a Century SAW. The other is a 2k lamp in a Cinemechanica console behind a Vic 5.

Both are reading about 5fL in the middle of the screen with a brand new lamp evenly lighting the screen.

The reflectors appear to be in good condition, the lamp is aligned, etc. But the image is still very dark.

Where do I start?

Posted by Jonathan Worthing (Member # 803) on 08-09-2011, 04:20 AM:

A bit more detail.

What is the size of your screen.

Posted by Dominic Espinosa (Member # 2122) on 08-09-2011, 11:44 AM:

I don't have the exact numbers in front of me. For the first house the width is around 25', common width.

The other is roughly the same, maybe ~30'

Posted by Tony Bandiera Jr (Member # 2365) on 08-09-2011, 03:52 PM:

EDIT: Just noticed a red flag..you said brand new lamps..did someone leave the protective covers on?!?!

You have a serious misalignment issue..2k is more that enough to get you to 16fl on those size screens. Hell, UC Irvine is shooting a 26' wide pic at 19+fl with 1.6k bulbs.

Recheck (with a laser kit if possible) the height, lateral and azimuth and tilt of those lamphouses...and make sure the "snout" to aperture distance is correct.

The LP lamp is very efficient and so is the Cinemech...so something is still seriously wrong with alignment or bulb focus.

Posted by Mark Gulbrandsen (Member # 72) on 08-09-2011, 06:40 PM:

The Cinemech should do well. The LP is an antique reflector and nothing to write home about. LP lamphouses are very well built though.

Mark

Posted by Richard Hamilton (Member # 321) on 08-10-2011, 01:28 AM:

quote: Tony Bandiera Jr
Recheck (with a laser kit if possible) the height, lateral and azimuth and tilt of those lamphouses.

Reminds me of a funny story. When I was working at Ballantyne I went in to talk to the guy aligning the lamphouses. Cool guy, maybe mid twenties. I had some time to kill, so I asked him to show me what he does. He had a laser kit that was made there. when he got done, he took the mirror out of the reflector, it was machined there. I asked him if I could look at it because I noticed it didn't fit very snug in the reflector. When he handed it to me it rattled. The damn mirror inside was loose. I put it back in and moved it around and rotated it, and the laser reflection was moving around everywhere. He said "dude, I'm just doing what they showed me to do". I laughed and told him just to get them close, I check the alignment when I install them because they get bounced around so much from the factory to the booth.

Dominic, is this a new install or were you just changing bulbs and if so what was the light output before? Have you checked the amps and volts, also the 3 phase coming in? I've had to change a few breakers in the panels because the electricians didn't tighten them good enough. I've also had to change contactors in the consoles for the same reason. I started terminating my own power on installs and tightening the breakers at night when they were gone.

Rick

Posted by Dominic Espinosa (Member # 2122) on 08-10-2011, 03:54 AM:

Thanks guys.
Richard, current all reads normal.

In the Cinemechanica it's got a new contactor, new diodes, and relatively new capacitors.
As well as a new reflector.

The LP has a reasonably good condition reflector, older Christie rectifier. Power was a little low, tweaked it up but nothing else seemed to be wrong with it.

Our preferred electrician (years of experience doing theater electrical specifically for us) did the panels so I'm confident in the connections being tight.

These are separate locations. I took over oversight of the projection, facilities, and operations management in whole last year and have been working through a back-log of issues the guy I replaced had left standing.
Some for years on end.
These, unfortunately, were not the highest priority; you can imagine the state of affairs.

But I digress...I was afraid I'd have to get up close and personal with it and diddle with alignment. Ugh.

Posted by Brian Guckian (Member # 1678) on 08-17-2011, 06:06 PM:

I encountered a problem last year with low light level due to incorrect arc position in relation to the focal point of the mirror. Even though a spacer was being used, it turned out that this particular lamp needed a slightly longer one, which made all the difference. Just wondering if that might be a possibility here.

Posted by Frank Angel (Member # 248) on 08-18-2011, 06:49 PM:

Tony, could someone actually leave the cover on a lamp? [Eek!]

Scary stupid. And also, wouldn't it like instantly melt or something equally horrid? I am imagining a lamp explosion after a few minutes running time...the thing wouldn't be on long enough for anyone to notice how dim the picture was!

Posted by Monte L Fullmer (Member # 2797) on 08-20-2011, 06:16 PM:

lenses burnt, or the light eating type, if rest of the optics comes out on track?

Posted by Phil Ranucci (Member # 3820) on 08-21-2011, 02:10 PM:

On the LP reflectors, have you checked that the nut holding them to the mount is tight? I've seen them get loose and the reflector droops and it really kills the light.

Posted by Tony Bandiera Jr (Member # 2365) on 08-30-2011, 12:59 AM:

quote:
Tony, could someone actually leave the cover on a lamp? [Eek!] Scary stupid. And also, wouldn't it like instantly melt or something equally horrid? I am imagining a lamp explosion after a few minutes running time...the thing wouldn't be on long enough for anyone to notice how dim the picture was!

Frank, yes they can, I have seen it happen. LP used to have a bulb on display in their lobby with the cover melted on it.

It will melt pretty instantly, and depending on a number of factors the bulb will not likely explode. The residue can stay cooked onto the bulb envelope for a long time too, so that's why I brought it up.

Phil, good point on the reflector nut. [thumbsup]