The out-of-focus behaviour of the 80-200 mm f/2.8 ED AIS is exemplary. Although its near limit is just shy of 2.5 m, quite tight environmental portraits of larger flowers and plants are feasible with the zoom extended towards its 200 mm setting.
This is Anthemis tinctoria on a timber storage area, where it thrives on the sandy soils. It is not strictly a 'weed' though, merely a coloniser of dry calcareous ground.