A Canon Extender EF 2x II, fit in my Canon EF 75-300mm lens?
It is generally recommended for telextenders f2.8 lens openings of/4.0. Here is a link that should tell you everything you want to know http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=ModelTechSpecsTabAct&fcategoryid=216&modelid=7463 # ModelDetailAct This is perhaps what you need to read: "With the EF 2x II, AF is possible [...]