Film-Tech Forum ARCHIVE: Lamp too bright

This is topic Lamp too bright in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Phil Ranucci (Member # 3820) on 01-27-2019, 10:08 PM:

Barco DP19 with a 3000 watt lamp.
Output is way too high >35 ftlamberts.
I can turn the lamp down to the minimum but it's still too hot, over 20ftlm.
Running at minimum also can cause flicker issued in the future, a smaller bulb isn't currently an option.
Will defocusing the lamp do any damage to the mirror or lightpipe?
Thanks

Posted by Dave Macaulay (Member # 813) on 01-28-2019, 06:16 AM:

(Duplicate, please delete)

Posted by Dave Macaulay (Member # 813) on 01-28-2019, 06:21 AM:

I recommend you align the lamp to max then pull the cathode back to defocus, counterclockwise on the Z adjuster. Maybe doesn't matter but I have seen damaged integrator parts apparently due to bad lamp alignment... expanding the beam spot rather than going through its minimum should avoid that.
If the LSC file was calibrated, the brightness reported will be in the ballpark but far from accurate. If calibrated at 35 it won't be very accurate except close to 35, to get a trustworthy 14 it should be recalibrated at 14..
I have tried installing a lamp as a lower power lamp (4kW as 2kW for a new 20C) to allow lower minimum power and brightness. It worked ok, no flicker, but yours may not like that. Barco sends a max size lamp with new projectors and I didn't have a smaller on at hand.
Defocus will shift color a bit, 99.999%+ of people won't notice... but probably out of DCI tolerance. Which no commercial cinema cares about.

Posted by Leo Enticknap (Member # 534) on 01-28-2019, 01:46 PM:

We sometimes encounter this problem installing laser projectors in high end home theaters (for which, obviously, you can't defocus the bulb).

The only solution for that is an ND filter in front of the lens.

Posted by Sean McKinnon (Member # 612) on 01-28-2019, 03:26 PM:

This probably wont help you today but there is a smaller aperture you can install on the integrator rod available.

Posted by Jarod Reddig (Member # 6363) on 01-28-2019, 03:34 PM:

Was going to recommend an ND filter but Leo beat me to it.

Posted by Peter Hall (Member # 695) on 01-28-2019, 11:53 PM:

Better to place the ND filter (or I agree, an aperture near the ND filter) in the light engine than after the lens. Contrast suffers horribly otherwise

Posted by German Marin (Member # 918) on 01-29-2019, 07:17 AM:

Install a 2000W lamp...

Posted by Monte L Fullmer (Member # 2797) on 01-29-2019, 01:33 PM:

Seen DP19 with 1200w lamps installed..