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Message: <blockquote data-quote="Overread" data-source="post: 1310465" data-attributes="member: 68571">unless the 70-300mm is a special case then the Canon teleconverters (call extenders specifically) will not attach to anything but L grade lenses due to the fact that they have protruding lens elements which prevent connection. The only way to connect the two is to use an extension tube to separate them - but that of course leads to loss of infinity focusOther brand teleconverters will attach (though again I am not certain if there are others which might have physical connection problems). There is also the chance with 3rd party TCs that they will either be non-reporting or that you can tape over the pins to retain AF - however the AF aperture limitation is there for the reason that once you breach the limit AF is not reliable.</blockquote>