Canon EF 400mm f/4 IS ii DO vs. EF 300mm f/2.8 IS ii L for Bird Photography: 4 Months of Experiments 

In this video I will show you the results of 10 key experiments which will help you decide which one of these professional-quality, low-light, light-weight lenses is the best for bird photography. experiment topics included testing for sharpness, bokeh, focus speed, how the 400 DO handles teleconverters and responses to stopping down.
The results were a little surprising!
DETAILED TABLE OF CONTENTS COMING SOON:
10:15 - Experiments Start
59:02 - Conclusions