Master List of Weatherproofed Lenses

Its not a case of one or the other, you would need a weather sealed body and lens to get the protection and even then it is not complete without a filter on the glass of weather sealed zoom .

They may not change overall length, but if they didn't move the elements and groups around internally they couldn't either focus or zoom. Changing the size of the internal chambers, however it happens, has a potential to suck in outside air.

The 28-300 is the same design as the 100-400, only with tighter seals and the gasket. The trombone type zooms do not push or pull any more air than a twist zoom, such as the Sigma 50-500 which in fact moves more air. Even the sealed lenses like the 70-200 move air internally when zoomed.

Another urban myth I'm afraid, usually spread by those with no long-term experience of the items in question.

The 100-400mm isn't weathersealed... So its chances of sucking in contaminents are greater than with a weathersealed lens. But sure, the air has to come from somewhere regardless of design. I would imagine the O-rings of sealed lenses decreases the size of the particles that can be sucked in or lowers the chances somewhat.

Cosworth, where is the list of weatherproofed lenses?. Thanks