This is a very popular, small and light-weight head. The panning base on this head does not lock as well as that on many other heads. The panning base features two anodized aluminum serfaces rubbing against one another. There is very little friction, but there is the possibility of these surfaces becoming damaged if grit gets between them. The distance between the center of the ball and the plate-support surface of the clamp is 1.85 inches.
We generally do not recommend the combination of the sidekick and the Acratech for lenses larger than a 300 2.8. Nevertheless, some of our customers report complete satisfaction using the Acratech with the Sidekick to support a 500 f4 lens.