Vivitar TX 300mm f5.5

      Tokina made this 300mm.   It is a TX mount lens.   I tested it on my T2i  with an M42 mount adapter.    It is heavy and I mean heavy.   It is all metal with a tripod collar.   You will need a tripod when using this lens.   On a subframe body it is impossible to hand hold.    I tried it with a monopod and I couldn't hold it steady.    The shots below are taken with the lens sitting on a bean bag.  

     Minimum focus is approximately 18 feet.   The lens has a long focus throw allowing for precise focus from 20 to 200 feet.   Focus dampening is perfect.  
     Sharpness is acceptable at f5.5 but contrast is low.  I boosted contrast in the three selective focus shots below.  At f8 contrast is better.  Sharpness at f8 is slightly better than f5.5.

     Bokeh is pleasing.  This lens is designed for patiently taken wildlife photos.   This is not a grab 'n go lens.
     Fringing is well controlled.   Distortion is low.    I did notice some blow out in highlights  when overexposing by two stops.   

     If you have a good tripod and good lighting this lens will produce excellent shots but it can be a bear to manage.    I suggest using f8, but f5.5 is usable if you are not cropping for enlargement.