Thank you for this helpful information. I recently bought the 70-300L for an upcoming African photo safari and I've been thinking about getting the Kenko 1.4 TC. I have both the 6D and the T1i. Any further thought/advice on the Kenko or other TCs would be appreciated. For example, I know that there are other TCs on the market, such as Tamron's and Sigma's, yet I haven't been able to find much in direct comparisons to the Kenko. The comparisons generally seem to be between the 3rd party and Canon, which isn't helpful since the Canon TC won't work on the 70-300L. Your comments as well as postings or links to other photos taken with the 70-300L with a 1.4 TC attached will be appreciated.