I got to use the 400 DO (also borrowed) the same day. With my 1.4TC. Great results also. My only issue was that I found it really awkward due to its shape and had great diffuclty raising it up to my eye and finding the subject. I do not have this problem with my 100-400ii nor did I have it with the 500 once I got used to it. PRobably I would get used to the 400DO, MedicineMan uses his with GREAT results and it is his favorite lens. I just found it really strange to use. It is a fine lens.
Here is one from the same afternoon taken with the 400DO plus Canon 1.4TC (latest model). I have several better examples but they don't fit on this thread as they were shot with a 7Dii-I only took two photos with the 5DIV and 400DO plus TC combo. I tried both lenses with both bodies, with and without the TC, to get a real feel for them in a real life shoot situation. Which was a boat at a wading bird rookery. A real test.
If you want me to post the two 7Dii flickr shots let me know, I don't want to spam the thread.
forum: Canon EOS Digital Cameras
That is crisp. I checked CPS Canada and they have both the DO and 2X III for rent.