jcolwell Online Upload & Sell: On
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Hi Carl,
The most common name is "dust trombone".
Both names are equally inappropriate.
The 100-400/4.5-5.6L IS is a full-up L-series lens. It's not (quite) as sharp at most focal lengths as equivalent L-series prime lenses, but none (or only a few) of the zooms are. This is because a zoom lens is a working collection of compromises, in comparison with a prime lens with optics that are optimized for a single focal length.
No need to apologise for wanting to use this lens.
I bought a new one in Jan 2012, and I use it quite a lot. I just checked its innards, and if I was going to sell it today, I'd say (about dust), "has a very small amount of internal dust - no effect on image quality at all". That's as good as, or better than, what I've said for 95% of the other 224 (and counting) lenses that I've sold (with 100% user satisfaction).
There is one maintenance issue that I'm aware of for this lens, and others like it (e.g. 28-300/3.5-5.6 L IS). The zoom tube has a rotating lock collar at its base, that you use to lock the lens at any particular zoom setting. I normally use this to lock it at 100mm, to avoid "zoom-creep".
If somebody tries to zoom the lens when the zoom-lock ring is engaged (i.e. it's locked), it can wear/strip/mess-up the locking gizmo, and destroy the gasket that is a central part of this gizmo. From what I understand, this is not a particularly expensive problem to fix, but it's something to avoid if you're looking at used " 'bones".
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