Which extender for my R5II and 100-400 L USM II

[Chickadee12]

I want to get a 1.4x extender to give me a little more reach.  (I know others that do this and it works well with very little difference in quality.  I think the 2x extender might limit me too much in lower light situations.)  I of course use the R to EF adapter.  Should I get the R 1.4x or the EF 1.4x III extender.  I have read that most use the EF,  but in the future I may change to a R lens (depending on what Canon comes out with) so wonder if I put the extender next to the body and the adapter next to the lens will that work? 

Anne

[deebatman316]

Hi @Chickadee12 RF Teleconverters designed NOT to mount to the EF-RF Mount adapter. Your only choice is the EF Teleconverter. I would highly recommend using the Mark III Teleconverter if you have to use a Teleconverter. I person recommend using a lens that has the correct focal length. As Teleconverters reduce the amount of light entering the camera. Also the AF motor slows down too. Not to mention that the lens may take an optical performance hit when a teleconverter is used.