Quote: Since normal metering is handled off of the focusing screen (I think), I wonder if that is what it's doing, dropping the mirror down, metering and swinging it back out of the way. Weird to do that, but maybe simplier than writing new code to meter off the sensor ?
I think that's exactly what it's doing. Because lens is not stopped down to the selected aperture (with manual lenses) when Live view is used - camera has no way to tell what aperture/shutter speed combination is needed unless it stops down the lens and meters. Now, why it drops the mirror to use the usual way of metering instead of sensor metering (like, without dropping the mirror, stop down the lens and meter off of that) - I'd guess because the former faster.
Say, when doing video with manual lenses - when you change the aperture, brightness shifts, and then camera adjusts back - but that takes quite some time, right? Maybe metering the latter way will require some time as well.
Quote: The K-7 LV knows it and shows real time blinkies and histogram or are we talking about something different (must be as Gus owns a K-7 and would have mentioned it, no?)
Okay, try this. (I don't have a K-7, so just guessing right now)
Put a manual aperture lens on the camera (K-mount, non-preset), or an automatic one, with aperture ring off the "A" position. Set aperture to something other than wide open.
In M mode, switch to Live View. Now, look at the lens. If it looks stopped down, then yeah, K-7 sort of "knows" off the sensor what shutter speed to use (because the lens is stopped down in Live view; with K-x, all manual lenses are not stopped down to selected aperture when in Live view). If not - then it doesn't.