No teleconverter today,just the Canon 400 L lens on my Rebel t2i. Lots of eagles today on a cold Iowa winter day. Stood outside my car door and rested camera on door. I did as Jim said and cranked up the ISO to 400 and lens speed at 1/2000 F5.6. I think it is better. I missed a lot of shots out of focus etc. Hard for me to keep on them while they are flying.
Ya got a wonder what they are thinking.