Really Right Stuff 80mm Sliding Multi-Purpose Rail

The MPRS-40 and MPRS-80 are made for the Canon 800mm and 600mm F/11 prime lenses. These lightweight, extendable lenses makes proper balancing difficult; the MPRS-40 and MPRS-80 solve that problem by allowing the foot to slide back to the balance point when the lenses are extended for use, and forward when in the stowed position. The MPRS-40 is best for lightweight setups like the RP or R6 The MPRS-80 is best for back heavy setups such as when using battery grips. Since the lenses lack a collar, both plates include holes for mounting the optional L-plate to the foot, allowing quick and easy vertical orientation.