The Sidekick is ideally suited for lenses similar in size to a 300 f/2.8 or 500 f/4.
Smaller Lenses: Many of our customers use smaller collared lenses on the Sidekick; however, when used in conjunction with a large, heavy camera body (e.g. a pro body with vertical grip), these lenses can be difficult to balance properly. Generally, 400 f/5.6 and 300 f/4 fixed or zoom lenses with medium-weight camera bodies work well. Heavier camera bodies on theses lenses can be problematic (even more so on 70-200 f/2.8 and smaller lenses).
Larger Lenses (600 f/4 & 400 f/2.8): The Sidekick will safely carry the weight of a very big lens provided it is mated with a ball head that will hold the weight of the lens. However, in some cases it is necessary to replace the foot of the lens with a low-profile Lens Replacement Foot, or add special spacers to the Sidekick to make the lens dimensionally compatible with the Sidekick.