Re: long focal length for macro:
The longer focal length gives you a longer working distance for the same
reproduction ratio. Might be helpful for skittish or dangerous subjects. The
long zooms that focus close would not be as good as a dedicated macro lens,
though. Close focusing in a zoom is mainly a "convenience" for the general
photographer. One exception would be the Vivitar 90-180, which was designed
from the start as a special medical macro lens. Even it is probably not as
good as a single-focal-length lens.
HTH,
Greg
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