Quote Originally Posted by Trevor Ash
Hi.

You're shooting at a faster shutter speed than the camera is capable of while syncing with the flash. They call this the "flash sync speed". On many camera's it's around 1/200 of a second or so.I don't know what flash you have or how it interfaces with the camera but you'll need to look at the instruction manuals for both to see how to properly deal with max flash sync speed.

It's most definetely not your lens causing the problem.
Trevor -

Thank you. This makes perfect sense, and it's exactly what appears to be happening in the images - I can imaging the shutter heading down before the flash has finished flashing. Or something like that.

I'll play with it & see what fits. Thank you!

Michael