On Sat, Jan 28, 2012 at 08:36:37PM -0800, Larry Colen wrote: > > >> Interesting. Then why is it that if you photograph something like a white > >> table, or snow, using normal metering, it comes out grey rather than white? > > > > Because the meter is dumb. > > That is exactly my point. There's no need for a meter to be dumb when our > cameras have more processing power than supercomputers of not that many years > ago.
It's not processing power - it's learned behaviour. In fact, when you are in a dance club, your brain is doing almost exactly what you are calling "dumb" - subtracting out what appears to be a colour bias from the strange lighting, and adjusting the iris aperture so that the amount of light falling on the sensor falls within a desired range. But if you didn't know, a priori, what colour the walls of the club were, you wouldn't be able to tell if they were white, 18% grey, somewhere in between, or even light blue, primrose, or light green. What do you expect the metering to do? It doesn't know whether the table top should be in Zone I, Zone IV, or Zone VII. It can measure the brightest and darkest points of the metering area, and set the exposure so that most of the pixels fall within the sensitivity range of the sensor. That's what all modern metering systems do. In fact they go beyond that - they'll also recognise common patterns such as a dark central area surrounded by bright background, and bias the exposure to assume you're shooting a backlit subject, so you need to dial in a little more exposure. But relying on auto exposure metering under tricky lighting conditions is a pretty poor strategy. That's why your camera has a spot metering mode, and an exposure compensation setting - so you can take control of the situation yourself. Or you can go the whole hog, and use an incident light meter. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
