IQ with the Kenko extender 70-300L 5D3 vs 7D

[DavidC1980]

Recent equipment changes mean that I now have a 70-300L, a 7D and my newest piece of kit the 5D MarkIII.

My question is how would the image quality of the 70-300L on a 5D with the Kenko 1.4x extender compare to the 70-300L on the 7D?

My main use for the 7D + 70-300L combo is motorsports, however if I can cover this as effectively with the 5D, extender and 70-300L I could consider selling the 7D.

Has anyone compared these two combinations?

 

[Bluesmachine]

From experience with certain lenses I'd say the FF camera would show up any issues more. I've recently bought a canon extender to replace my kenko one (both x2) as I wasn't happy with the softness on the kenko. I used it with a 70-200 F4 on FF and 70-300 sigma & 70-200 f4 on crop.