Canon USA has today published a service advisory detailing a firmware update on four of its telephoto and super telephoto lens models for the pro market. In all four cases, the firmware updates autofocus algorithms for better responsiveness and more precise focus, especially when using AI servo AF to track irregularly-moving subjects. The Canon EF 300mm f/2.8L IS II USM and EF 400mm f/2.8L IS II USM lenses were announced in August 2010, while the EF 500mm f/4L IS II USM and EF 600mm f/4L IS II USM announcements followed in February 2011. All four lenses faced significant delivery delays,...
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