On Mon, 23 May 2011 15:57:48 -0700, the Legend of LAX wrote:

I don't know, my Canon 100mm-400mm USM IS L does a tolerable job.

100-400mm is not an extreme range.

By extreme range I am referring to zoom lenses that attempt to
capture both the wide angle and the telephoto focal lengths, e.g.
24-200mm. (I assume that 35-50mm is the dividing point between
wide angle and telephoto.)

100-400mm is within the telephoto focal lengths and so the design
of this lens is not that difficult (comparatively speaking.)

But any serious consumer should always check the MTF data for
the lens in question. Most manufacturers provide this data
somewhere, but independent MTF test data is the best.

Buying a lens is always something of a gamble. The on-line reviews
are not at all reliable, and any model of lens will exhibit variation
due to differences in manufacturing. Even MTF can be unreliable
because some MTF data is based on simulation rather than actual
testing.

I hate to sound pessimistic. I suppose that unless one is
obsessed with quality most high-end lenses will do a good
job.