Proper exposure requires several bits of information: - how much light is available to work with - how a particular recording medium reacts to light - what is important in the scene and where to place it in the range that the medium can record - what is unimportant in the scene and when/how to ignore it (or hide it)
In-camera meters operate on reflected light, which alters their assessment of how much light is available as the dynamics of reflection and absorption in the scene also causes variations in the meter reading. Live Histograms, review histograms, saturation/clipping blinkies are all tools to allow you to assess what the meter is seeing. Useful tools, but you still have to understand how scene's dynamics influence total exposure to make best use of them, and what exactly they are reading from relative to your desired output product from the camera. Hand-held meters can operate on both reflected and incident light. Incident light metering nets a more direct measure of the light falling on a subject regardless of subject reflectivity, relative to a calibration constant (usually 18% average reflectance). Reflected light meters are subject to the same considerations as in-camera meters, but can be used with optics to limit the area they are measuring, etc, for accurate assessment of the light values and comparison of same. I've never seen any useful benefit from trying to calibrate meters to digital cameras other than very casually. I more often take the strategy of using a good, reliable incident light meter as a reference against which to understand the behavior of the camera's sensor and metering system. A hand-held incident light meter is a simple thing and easily understood. I can use that understanding to determine whether the ISO settings on the camera are conservative or optimistic, what the dynamic range is in approximation for each ISO setting, and what the camera's metering calibration is set for. A couple of quick test shots with a triple-target (black, white, gray) with the camera set to the reference meter's recommendations for each ISO setting, and noting what the camera's meter recommends by comparison, provides all this information. My reference hand held meter is a Sekonic L328. I'd like to upgrade to the L-358 model sometime as it has a much larger integrating dome, a larger range, and is more accurate. I use the L-328 a lot: it provides superb light readings for use with all my cameras. -- Godfrey godfreydigiorgi.posterous.com -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
