Originally posted by Rickster I don't think that's an issue that can be solved easily in the camera. The basic problem is exceeding the camera's metering spec by attempting to use stopped down metering. Modern digital cameras need a minimum amount of light for their metering systems to work properly.
The K7 appears to be spec'd at ...
Metering range: EV 0.0 - 22 EV (ISO 100, 50 mm F1.4)
The K20D is spec'd at ...
Metering range: EV 0.0 - 21 EV (ISO 100, 50 mm F1.4)
the K10D is spec'd at ...
Metering range: EV 0.0 - 21 EV (ISO 100, 50 mm F1.4)
From this we can see that the K7 has added 1 EV of metering range on the high side.
EV 0.0 - 21 (ISO 100) is a pretty incredible range considering that EV 0.0 is 1 second at f/1. That is very, very dim. Interestingly, it is not too difficult to attain that dimness at the sensor when stopped down in moderately low light. I have had the display blinking with manual aperture lenses in Av mode at f/11. This type of limitation is present for all cameras capable of stop-down metering. In fact, it was not unusual for the manufacture to publish a graph indicating supported ranges for aperture/shutter speed/ISO back in the ancient days of stop-down cameras.
However, from all available evidence, the more metering issues are not directly related to meter sensitivity range except at narrow apertures in dim light. Increase the light level and underexposure at the narrow end disappears. The pattern of severe underexposures at apertures f/4 and wider (up to 2.5 stops) is related to focus screen design and mathematical correction factors applied by the camera to reconcile the meter readings with an acceptable exposure. (I.e. The camera's meter is not linear for stop-down metering with most screens.)
Steve
(Currently own two stop-down meter film cameras...both with linear meter response...)