Wimberley Sidekick
I'm excited about the purchase I just made. Unless you are familiar with the problems of mounting and using telephoto lenses, you may not recognize the gadget on the left. It's the Wimberley Sidekick -- a device that attaches to most tripod ball-heads such as Arca or Kirk (mine). A standard ball-head plate is then attached to the camera or lens (usually the lens). The plate fits into the holder you see at the upper right placing the camera & lens above the ball head. By adjusting the plate the whole camera/lens assembly can be brought into balance so that, when mounted on the tripod, the camera/lens can be moved in all directions by just a touch of the finger, making it much easier to catch birds in flight or simply to switch directions.
You can view the whole contraption by clicking here. The Sidekick will work with lenses up to 500 mm, although for the heavier 500s and 600 mm lenses a larger Wimberley is recommended. I'll keep you posted on how it works out for me.