[Tig] Measuring a DCI-theatre projector - new vs old lamp

Richard Kirk richard at filmlight.ltd.uk
Fri Mar 1 15:09:13 GMT 2013


> From: Carl Skaff<carl at stopp.se>
>
> Got a question. Has anyone out there done any measurements on a theatre
> projector with a new vs old lamp?

Hi, Carl.

I have been around when it happens a few times.

New arc lamps can be a bit bluer for the first few hours. I don't know 
why that is, but if it is like tungsten-halogen lamps, there is an 
equilibrium between the hot bit and the material deposited on the glass 
envelope that takes a while to establish.

More significant is the alignment of the lamphouse. You may have to 
twiddle several screws to get the lamp into the right place in a 
projector to get a uniform screen temperature and brightness. As you 
twiddle, you can be imaging different parts of the lamp, so the colour 
temperature goes up and down. If there is nothing to twiddle in your 
digital projector, this may not mean it is in the perfect position.

As the electrodes wear (it is an arc lamp, right?) the arc can change 
position. I think arc lamps are retired because they flicker rather than 
the colour drifts, but I bet there are plenty of people on the TIG who 
will put me straight if this isn't right.

> They said they just did a full calibration... But that was just BEFORE they
> changed lamps!!!
<wah_wah_waah.wav>

Cheers.
Richard KIrk

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