"FocusShifter is a stand-alone Follow Focus and Rack Focus with a focus marker board that can be used on any camera lens. No extra equipment is required. It's perfect for filmmakers, photographers, and anyone wanting to step-up their production capabilities with an inexpensive focus puller. It gives you professionalism without breaking your budget. The Shifter and Focus Marker Board attach quickly and easily to any lens ranging in diameter from 56mm (2.20in) up to 98mm (3.86in). If you're measuring circumference, distance around the lens, it fits from 176mm (6.93in) to 308mm (12.12in). It even works well on the popular Canon 50mm f1.8 lens, which is notoriously difficult to attach a follow focus to due to the design of the focus ring. Note: The ""mm"" markings on the lens are not the outer diameter of the lens. You must measure the outer diameter.|Nail Your Focus: The re-useable Focus Marker Board allows you to create marks for your focus points using a dry-erase marker. The arrow on the Shifter facilitates quick and easy transition between focus points. Pull focus like never before.|Hard Stops: Using simple clips that attach to the focus marker board, you can set hard stops which allow you to shift between 2 focus points by feel without ever looking at the marker board.|Simple to Install: To attach the Shifter, simply slip it over the lens, onto the focus ring and tighten it down with the ball end. The Focus Marker attaches to the lens with an elastic band, and has over-molded rubber feet to hold it in place.|Easy and Smooth: The Shifter allows you to smoothly pull focus without any jarring starts or stops. The ball design is easy to grasp so you can avoid twisting your hand into uncomfortable positions when pulling focus. For a lens with a narrow focus r|For Photographers Too: Using the Shifter improves manual focus speed and accuracy when taking photographs. It's especially helpful with lenses that have a shallow depth of field, and need fine adjustments. Get another one to use for zoom."