This is a very well-built telephoto zoom lens with a constant large maximum aperture of f/3.5 throughout the range. It is also very heavy and quite a bit larger than the other zoom lenses within that range (almsot as large as a 70-200 mm f/2.8 constant aperture lens).
The lens is a push-type zoom lens and has the longest telephoto setting when completely pushed in (unextended). There is also a special macro button which lets you extend the lens even further all the way to a maximum magnification of 1:2.5.
I haven´t had a chance to test the optical quality of this lens yet.