Vivitar 75-260mm f4.5

     Made by Tokina.  This lens is a bear.  Thankfully, it has a tripod mount.  It is impossible to hand hold.  I've begun testing it with my T2i but I think it will produce better results on a mirrorless body.  Critical focus is difficult to achieve on a D-slr.  The lens is made very well.  Zoom and focus rings are very smooth and well dampened,  F-stops click nicely.  It is reasonably sharp @ f4.5 and sharp at f8 thru the entire zoom range.  Contrast is noticeably low and color rendition is a bit flat.   Purple finging can be seen at 100% crop but well controlled.  Bokeh is less distracting than many tele-zooms but it doesn't compare to the smoothness of a prime lens.  This lens can be found for a very reasonable price.  If you don't mind lugging it around and doing a little extra post-processing of your images it can produce good results.