Canon EF Extender III 2X with EF 70-200mm f/2.8L IS II and 70-20mm f/4L IS

I've published a comparison using the new Canon EF Extender III 2X, showing how it performs with Canon EF 70-200mm f/2.8L IS II and the Canon EF 70-200mm f/4L IS. See my review in DAP.

The EF Extender III 2X acquits itself fairly well on the f/2.8 zoom, turning the f/2.8 zoom into a 140-400mm f/5.6. But the results at f/5.6 are not so useful in my view, making it an f/8 lens for reasonable quality. After all, 23 elements + 9 elements is a huge stack of glass, and any optical issues are magnified by 2X.

Canon EF Extender III 2X + 70-200mm f/2.8L IS II @ f/11, actual pixels