Originally posted by Adam , why not just use an EV compensation equivalent to the loss of light?
BTW, you'd expect it to underexpose rather than overexpose, right?
Loss of light is not the problem, any proper lightmeter
only measures the amount of light entering the camera.
The flawed K10D/K20D meter also changes readout when the shape of the light cone changes, and thats the problem.
Once determend, you can apply a fixed EV compensation for every pentax-A 2.8 lens in combination with the 2X converter (and for a F4 lens probably another compensation), but the cone of light also changes with close focussing.
Probably only Pentax knows how the lighmeter meters wrong as function of the angle of the light cone.