In LensRentals.com's recent tear down of Canon's RF 70-200 2.8 IS lens, Roger Cicala comments about extending barrel zooms and dust issues.
"Before we start, though, let’s get the extending barrel discussion out of the way. Some of you HATE extending barrel lenses. That’s cool; don’t get one. Some of you like to call them dust pumps. That’s cool, too, although it’s incorrect. (We take care of over 20,000 lenses. The most common ‘dusters’ among current lenses all happen to be primes that don’t zoom at all.)