Canon EF 200-400mm f/4L IS USM Extender 1.4X User Manual - Page 16

10. Internal Extender Switch The extender switch lever allows you to set the focal distance of the lens to 1.4x. Slide the extender switch lock toward the front of the lens. ●● This allows the extender switch lever to move. Use the extender switch lever to select a focal distance of either 1x or 1.4x. ●● This allows you to change the focal distance of the lens to either 1x or 1.4x. Slide the extender switch lock toward the back of the lens. ●● This locks the extender switch lever in place. The extender switch lock prevents the extender switch lever from being moved inadvertently. It does not secure the switch lever to the side edge. Be sure to use the lock even when the switch lever is set at 1x in order to prevent it from being moved inadvertently. When the internal extender is used (set to 1.4x), the AF speed will become slower to retain proper control. ENG-15