Sharington's Tower at Lacock Abbey

Tokina did not keep their 50-135mm fast zoom pro lens long in production. They may have misjudged the market for a lighter weight equivalent to the various f/2.8 70-210mm and 80-200mm lenses. Plus, the Nikon - compatible version needed a camera with a screw drive for the AF and not all Nikon digital cameras are so equipped.
The lens was a collaborative project with Pentax and the Pentax version is the only one to remain available new. It will set you back over £700. That is a measure of how good this lens is.