Originally posted by quarc It does not change anything, the behaviour is still non linear, and the camera can not compensate. How big the problem is depends on what lens you are using, and what aperture you are shooting at. This is why some people see very little problem, while others have huge issues. Using M helps only in the perspective that when you have found a setting that works, you use that until light conditions change or you change the apertue or lens. This is one of the situations I wish there would be a way to lock the settings as it is so easy to accidentally move one of the wheels.
/PA
My experience* with the newer generation bodies (K-7 on) is that M-mode stop-down exposure is pretty decent and linear within the sensitivity range for the meter**. Av mode with M42 lenses essentially sucks however, for the reasons you described. That is why modes other than M are annotated in the user manual as being likely to result in exposure error.
Anyone interested in testing the linearity of their camera's stop-down metering can PM me for detailed instructions.
Steve
*Not as owner, just as in-shop evaluation with my own flash card and lenses.
**Use of a narrow apertures in dim light for stop-down metering can easily overreach the linear range of the meter. This is true regardless of set ISO. In the old days the user manual would have a table indicating the limits, but now the user has to calculate it out manually.
Example: The K30 has a meter sensitivity range of 0-22 EV(100). A subject indicating an exposure of 1/15s @ f/8 for ISO 100 (e.g. dusk) would provide only -1 EV(100) to the meter at f/8 using stopped-down metering and would be outside the built-in meter's linear range.