Some lens and Extender combinations mean that you will not be able to autofocus. Not all EOS cameras have the f5.6 limit. Some allow focusing at maximum apertures down to f8 and, with the introduction of the EOS R full frame mirrorless system, this is now further extended with f22 compatibility.
This is what we mean when we talk about autofocusing at f5.6 or f8 – it is all about the maximum lens aperture and has nothing to do with the aperture selected for the exposure.
Canon Extender compatibility
Compatibilty is a double-edge sword when it comes to Canon's Extenders. All lenses listed below are compatible with Canon Extenders.
However, in this instance ‘compatible’ simply means that the Extender can be attached to the lens, not that full functionality is retained. Autofocus and image stabilisation may not work with some lens and Extender combinations on some camera bodies.
If autofocus is lost, you can always focus manually. This is often a preferred option as the AF speed can slow down when an Extender is fitted, even in bright light.
