Originally posted by stevebrot I think you are probably right and I have probably been not thinking clearly due to wishful thinking. Yes, the system needs to know the offset from maximum aperture to calculate the shutter speed unless the lens is at maximum aperture.
Steve
I don't think it needs to know anything about the absolute or relative value of the lens aperture to set the shutter speed.
If the system can stop down, then measure the amount of light, it's basically trivial. This is how the camera does it for M42 lenses now, just with human intervention to do the stopping down...
As I understand the system, the camera stops down the lens to whatever it has been set to, then takes a meter reading, which informs the shutter speed and ISO settings according to whatever program line is in place.
The only part I don't get is where the meter reading is coming from at that point.
Is the camera stopping down, metering, then flipping the mirror up? That sounds time-consuming...
Or is it metering off the main sensor, as it would do in live view?
So stop down, mirror up, shutter opens, meter reading, camera picks shutter and ISO as appropriate, then shutter closes?
That gets complicated... and would require the electronic shutter, not just the mechanical one...
-Eric