Barrel distorton is not the worry - if anything it's pincushion distortion that might appear. I too have one of these fine C8 telephoto converters and use it with my VX2000, where I need a 58 mm > 62 mm step-up ring.

But whatever were Canon thinking when they made this big and heavy optic? OK, the build quality is fine and the image is excellent, but what were they thinking when they decided to apply no lens coatings at all? The 1014E and XLS had beautifully coated f/1.4 10x zoom lenses, yet this lens effectively destroys all that.

All I can say is use a good, deep, black, cylindrical lens hood with this baby. As you can't zoom back far the hood can be deep and efficient. Keep non image forming light off that huge front element.

tom.