EF 600mm f/4 IS II
Another challenging condition is when the raptor flies towards the camera against a varied background, since the motion is perpendicular to the AF sensor. The EF 600mm f/4L IS II performed well for this type of flight as well. Below are examples with the kite flying towards me. The juvenile had just captured a vole and was gliding quickly to get out of the danger zone. A large percentage of frames from this sequence were tack sharp. Although a quantitative comparison in these conditions is not possible, I feel the focus precision has improved at times. According to Canon, the series III EF extenders feature a micro-controller that can communicate with the CPU fitted inside the series II super-telephoto lenses. The micro-controller stores some correction factor that can improve AF precision in AI-servo tracking mode when used with the new lenses. According to Canon, the series II super-telephoto lenses also feature a faster CPU and improved AF algorithms to achieve a faster focus speed. Overall in my experience both the servo drive speed (AF acquisition) and precision seem to have improved, in particular the AF drive speed with the EF 1.4X Extender III feels extremely quick and perfectly usable for the most challenging conditions. The focus limiter switch has now been placed at the back of the lens, by the camera mount making it inconvenient to set the switch when handholding. It would have been better to place this switch with the rest of controls.
Overall the performance was stellar in holding focus on incoming kites against different varied backgrounds.