A lens that changes length through the zoom range will change the front and back balance of the setup. However, the Helix’s stabilization motors can compensate for the weight shift. There would be no need to re-balance the Helix when changing your zoom range on most lenses. For example, the Canon 70-200mm f2.8 L series has been used on the Helix in-house without issues. As long as you can reasonably balance the setup front to back, the lens length is not a problem.