Quote Originally Posted by HDNitehawk View Post
http://www.the-digital-picture.com/R...mp=0&APIComp=0

Bryan has the chart for it. The 300mm F/4 with the 1.4x III is not as good. Since you have the 70-300mm L I don't think it would be a good option.
for 70-300mmL, you will lose AF at 300mm with the TC.