Not sure if this topic belongs here, but anyway here goes ...
Shooting a soccer tournament with Elan 7 in harsh/strong sunlight (f4 w/ TC, 1/4000), Fuji Superia400 & Press 800, 120mm-300mm EX with hood & 1.4 TC, approx. 50% of backlit or strong sidelit shots showed moderate light falloff. No problem on the one overcast morning, however, and little to no problem when light was at my back. All aperture priority, partial metering.
I have never experienced this problem without the teleconverter.
Any advice on cause or how to avoid in future is much appreciated.