Tamron likes to do things a little differently than others and often creates slightly more unusual focal lengths than what is usually considered traditional.
One such example is the Tamron 70-180mm f/2.8 Di III VXD, its take on the classic 70-200mm f/2.8 lens (considered a part of the "holy trinity" of professional zoom lenses). Shaving 20mm off the top end made significant weight and size savings, while not sacrificing the wide aperture or image quality.
