Tamron 70-350 mm f/ 4.5 Adaptall-2 model 05A Lens

Central sharpness is excellent and build quality is very high.  It offers a constant f4.5 across its focal range.

Weaknesses:

This is not a lens for hand-holding!  Edge definition at f4.5 is pretty fair but not outstanding.  Like most long zooms, it is a little soft at its longest focal length though in the case of this lens, it's better than most. 

Comments:

This lens demands respect.  It is big and heavy but produces great images.  When mounted on a good tripod with a fluid head, it is great for shooting aviation and wildlife photos.  I have also known it be used for surveillance work by the police and military.  If it used some low dispersion glass and internal focusing, it would be amazing but despite the absence of both, it will deliver images of detail, with low distortion and even illumination through most of its focal range.