While I can't say that I've taken my copy of the 100-400L lens onto five different continents like @smirkypants, I have used it pretty extensively for the last couple years in some of the worst weather Colorado has to offer. I've used it in torrential rains, near-whiteout blizzards, sub-zero temperatures, and highly dusty winds. Even though it does not carry a "weather sealed" label, I've never gotten any moisture or dust inside of the lens, and I've never noticed any accumulation of dust on my sensor due to its use.
While I don't have any patents or diagrams to back it up at the moment, I think its a bit naive to think that Canon did not design this lens with an adequate filtration system around the push/pull design. Yes, the lens sucks in air, but its highly unlikely it directly sucks in unfiltered air.
While I don't have any patents or diagrams to back it up at the moment, I think its a bit naive to think that Canon did not design this lens with an adequate filtration system around the push/pull design. Yes, the lens sucks in air, but its highly unlikely it directly sucks in unfiltered air.
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