Originally posted by Lev Guys, how do you think, or have you seen some info where Pentax claims that zoom AW lenses, like 60-250 are as well rugged as prime lenses? Because, as all we know, zoom lenses that extend from its barrel tend to be more vulnerable against dust and moisture.
Dust is generally not a problem unless photographing sandstorms is your line of work.
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Moisture, eh, it's insidious and will get anywhere and everywhere. Best to not let the camera in the rain for a long time, regardless of lens type, weather sealing, brand or anything.
Zooming in and out is normally not too problematic unless the barrel is caked with dust when you pull it back (grit problems) or very wet. The volume of air sucked is low and the velocity of the flow is also not too much so the seals in any decently WR lens would trap the small amount of dust in "normal" environments.