Film-Tech Forum ARCHIVE: Light Readings

This is topic Light Readings in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Jonathan Althaus (Member # 5042) on 01-04-2010, 06:37 PM:

I hear all the talk about low fL readings for digital projection, so I decided to take a look at our lone digital projector. According to our touchpanel, during 2D we're getting around 40fL and in 3D it's reading over 35fL. Are these readings horribly wrong, or is our projector just awesome?

Posted by Brendan Penny (Member # 5041) on 01-04-2010, 06:45 PM:

That only tells you what the sensor in the lightpipe is getting and if that sensor has not been calibrated to the actual light output that could also be incorrect. The again, if you are using a large lamp for 3D and not downsizing for 3D, 35fl for 2D is not at all un-common. It is recommended that a smaller lamp be installed for 2D use which I know is a pain the the ass and no one I know does it!

Also, only way to measure 3D output is to meter behind the 3D glasses.

But yes, your projector sounds pretty awesome!!!

Posted by Brad Miller (Member # 2) on 01-04-2010, 06:53 PM:

Ummm, yeah.

Posted by Julio Roberto (Member # 4976) on 01-04-2010, 06:55 PM:

Your projector is awesome and you need sunglasses urgently [Cool]

It wouldn't hurt to measure the light bounced from the screen instead of the touch panel readings. In 3D, you also need to do it through the glasses' filters. [beer]

You may find the procedure to calibrate the readings so the match the reality in your projector's manual. It would go something like this:

quote:
In order for the TPC to display screen brightness in footlamberts (fL), you must measure screen brightness at both extremes of lamp power (minimum and maximum) for a given lamp type, and record these two readings in the TPC Admin: Lamp menu available to installers. These measurements establish a range (stored in memory) from which the TPC can interpolate all other lamp power PC can interpolate all other lamp power settings, converting them to approximate footlamberts for display in the menus. Repeat the calibration if you ever switch to a different lamp type/size.

This changes with projector model, of course, but you get the idea [Wink]

Posted by Jonathan Althaus (Member # 5042) on 01-04-2010, 07:09 PM:

Ok, I thought the readings were high. Not that we run 3D on it anyway, still running New Moon in digital.