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Author Topic: Luminance Uniformity Falloff Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 10-24-2017 10:25 PM                     Lucas, the 14fL only has meaning if the rest of the specification is followed (at least 75% in the sides/corners). A flat silver screen will NEVER make that so all bets are off. Anyone that sets 14fL in the middle of a silver screen is going to have a very DARK picture. In fact, anyone that sets 14fL in the center of ANY screen with a gain over 1.3 (and flat) will have a darker picture (overall) than a lower gain screen and will be out of spec. Through testing, I've found you just can't go above 1.3 gain on a flat screen without excessive hotspotting. I kindof agree with Marco on this but I took it a step further. I measured a screen (Stewart Ultramatte 130) that measured pretty much right at the limits of SMPTE/DCI spec in terms of uniformity. I measure using a PSA type meter (45 simultaneous readings across the entire surface). I then used that to create what one would have to normalize an out of spec screen (above 1.3 gain) such that it would have an approximately similar overall light level. If you use a typical Silver screen with about a 2.3 gain, and set the center to 19.6fL you'll get something with a more acceptable overall light level. If you are trying to get the same appearing light level as a matte-white running at 14fL (the goal), then Marco is right, 21.8fL is closest.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 10-25-2017 04:22 AM                     Lucas, I take measurements on Left, Centre (yes, hotspot), Right, Top and Bottom. Then do an average and adjust the centre to achieve a 14fL. I appreciate this is not a super-accurate measurement (you will need more readings to achieve a good average) but as mentioned we are just trying to limit the damage here. Your edges will always be completely off and your hotspot too. What you are doing here is to make the picture look pleasant. Setting 14fL on the hotspot/centre is NOT going to achieve that goal!  |  IP: Logged

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