The Sigma 500 f4.5 has always been internal focussing, they never made one where the front of the lens turned with the autofocus. Even the Sigma 500 f7.2 was internal focussing. Can you imagine the problems turning the huge front element in the 123mm dia barrel would cause, the motor and or gearing to turn this huge piece of glass would require a lot of power. Big drive motor, lots of batteries to power it!
nirofo.
Last edited by nirofo; 03-11-07 at 01:33.
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