The first 4 are from the Canon, the first two are without the extender and the second two with. The final four follow the same sequence with the Vivitar. The softness in the final four images is down to the Vivitar rather than the extender. Canon EF 2x III Extender Canon 6D + 100-400mmL II + 2x III Extender (monopod used). Canon 6D Mk1 + EF 100-400mmL II lens + EF 2x III Extender AF will not work via OVF but it will with Live View (same as the 1.4x Extender). AF speed will be UNBEARABLY slow but the image quality is still excellent. For Birding the image quality is excellent. Lens Extender compatibility with EOS 5D Mark IV and EF 70-200 f/2.8L IS II USM lens in EOS DSLR & Mirrorless Cameras 12-19-2023; Extender EF 1.4x III compatible with EF mount? in Camera Accessories 12-18-2023; EOS Rebel T6 Extender and Lens Recommendations in EF & RF Lenses 12-10-2023 Fotodiox EOS-2x-AF-Tele Black/Silver Pro Autofocus 2x Teleconverter Compatible with Canon EOS EF Full Frame Lenses and EF / EFs Cameras 3.5 out of 5 stars 309 $155.50 $ 155 . 50 I was torn between buying (used) an EF 70-200 L and a 70-300 L. The 70-200 could be used with an extender. The 70-300 could not. I reasoned that 200mm extended to 400 would be too much for me to hand-hold, involve carrying the extender around in case I wanted to use it. I'm glad I bought the 70-300. oMOyY.