>>It is my hypothesis that telephotos (except IF ones, of course) tend >>to exchange more air while focusing back and forth (with their >>usually longer helicoids) than do most wide angles, and so they end >>up sucking in more dust. ;-)
> Unfortunately, FA135/2.8 & FA*200/2.8 are IF, and they still suck more dust > than my other lenses. :( Oh well, so much for that theory... (Actually it was just a hypothesis - elevating it to a theory would definitely be stretching the point - <g>.) OK, here's another thought: Perhaps at least some of the IF lenses still suck air in (and blow air out) while focusing. Although the total air volume inside an IF lens may not change during focusing, it is still possible that, as the moving optical group shuttles forward and backward inside the lens, air could be alternately pushed out the back while being sucked in the front, and then pushed out the front while being sucked in the back. (???) ;-) Fred
