Canon Extender EF 1.4x II Tele Conversion (Accessory)
And presto ... that turned into my 70-200 100-300 5.6 ... cool. Beware of neophytes when Canon said diaph lose 1, this corresponds to around diaph (multiple of 1.414 - 2 root) So 4,5.6, 8, 11 ... no half value. Amazon delivery side, as usual nickel.