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Author Topic: Measuring Screen Luminance Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 03-31-2004 10:38 AM                        If my math is correct... EV = ln (fL / PI / 10) + 10  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 03-31-2004 10:59 AM                        I've used a photographic spot meter for reading a screen, after calibrating it against a Spectra Cinespot meter. Once setting the screen luminance to 16fL using the Spectra, I shot the same screen with the photographic meter and just noted the EV reading. Did this many times to verify repeatable results (I know some photographic meters have trouble integrating the "flash" rate caused by the projector shutter). With that particular photo meter (an old Minolta), the results were consistent, so I went on to use that meter during a four-month long dailies stint. A much cheaper solution than renting or buying a Spectra. IIRC, 20 fL is/was the SMPTE standard for luminance on CRT monitors used for television production. The camera shader I used to work with didn't use that standard though--he went with a lower level. Back then, some production and engineering monitors couldn't make 20fL on the 100IRE white bar.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 03-31-2004 12:22 PM                        Some articles: http://www.cctvlabs.com/TestChart/ev_luxes_cctv_focus_9.pdf http://www.kenrockwell.com/tech/ev.htm http://www.minoxlab.com/Don_Krehbiel/mpl/dkasa.htm Remember, 1 EV is a change in light level by a factor of TWO. So your meter needs to read accurately to discern screen luminance changes. Even if you have a meter accuracy of 1/3 EV, you will barely tell the difference between 16 footlamberts and 12 footlamberts: http://www.kodak.com/US/en/motion/newsletters/pytlak/june2000P.shtml#p  |  IP: Logged

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