archiea said:100-400mm:
1) internal design like the 70-300
How do you define 'internal design'? The 100-400 has rear 'internal focusing'. If you're referring to the way the lens barrels overlap, I prefer the way the 100-400 is designed, with the outer tube carrying the big front element, and the rear tube carrying the small elements. That is one of the reasons this is such a (relatively) compact design!
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