thc1979 wrote in post #18035279
I checked today and the extender I have is the x2 version ii. I tried it on my 5D3 with 70-200 2.8 is ii and at first it wouldn't autofocus at all, then I moved the focus ring and it sprang to life. Not sure how compatible it is with that lens, reviews and technical charts are bit confusing. They say autofocus needs f/5.6 min, does that mean I can't use a higher f-stop or does it just need that in the viewfinder? Also some reviews say image quality is degraded, canon say it doesn't affect iq at all.
If that extender is Canon brand then it is compatible with your 70-200 and bodies listed in your signature. Extenders do reduce image quality - 2x more than 1.4x. The Canon 2x version ii extender is "ok" but not outstanding, but what it will do is allow you to determine if an extender will suffice for your needs. If it does you could replace the version ii with the much better version iii extender for better results. If not, you're back to your initial post of working out which lens to buy...
thc1979 wrote in post #18036736
Do you think it would end up replacing my 70-200 though?
I agree that they are 2 tools for different uses, but the 100-400ii might somewhat replace the 70-200 depending on what you shoot. I think of the 70-200ii as my indoor / portrait lens, and the 100-400ii for outdoors / travel. Even in situations where I'm shooting motorsports / aviation using sub-200mm I still prefer my results with the 100-400 ii (unless available light is absolutely miserable).
Best case scenario is having both lenses - if you need f2.8 then you have the 70-200 - if you want reach you have the 100-400.