100-400 still a dust pump?

Started May 3, 2012 | Discussions thread
William Woodruff
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Re: 100-400 still a dust pump?
In reply to gdanmitchell, May 4, 2012

First a disclaimer: I don't have the 100-400, nor have I tested it in anyway, so the following comment is simply what I suppose to very likely be true.

Absent some thoughtful testing and documentation that finds otherwise, I suspect that the 100-400 is not significantly better or worse than most other well-built lenses with telescoping elements (regardless of whether they are push-pull,or rotational control. The reason that I believe this to be true is that any lens that has a telescoping design must necessarily change it's internal volume whenever it changes dimensions. When the volume of the lens increases, air has to get in (I am discounting the possiblity of creating a vacuum inside the lens.) When air gets in, dust will get in as well. The amount of dust that gets in, and the maximum size of the particles will be limited by the fit of the seals between the telescoping elements.

None of the above seems to reasonably apply to any greater or lesser degree to a lens based on whether it is controlled by push-pull or rotational external movement.

With that in mind, I suspect that the real reason the 100-400 got a reputation as a "dust pump" is because the push-pull zoom control resembles a "pumping" action, and therefore suggests a problem that does not necessarily exist.

The only thing that looks like a real answer for the truly paranoid, is to stick to lenses that focus and zoom internally, and therefore are not required -- by design -- to force air in and out repeatedly. (E.g., the 70-200 zooms.)

Just my thoughts on the matter.
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WLW

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