JMZawodny said:So lenses like the 500L f/4 with the 2x extender can only use 9 AF points (pages 107 and 110)???? This seems to go against the myriad claims that f/8 could use all 61 AF points. A major let down if true.
My reading indicates that it matters whether the 2x extender is version i/ii or version iii. For the version iii, the key wildlife lenses (400 do ii f/4, 500 f/4, 600 f/4) are all in group F (61 points) at f/8 but for version i/ii, they are in group J (9 points). This is particularly important for the 400 do ii which has relatively little IQ deterioration with the 2x TC (iii), and therefore represents a reasonable alternative to the 500+1.4 or 600+1.4 for extensive hiking or traveling where weight is a critical factor.
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