In message ,
"Roger N. Clark (change username to rnclark)"
wrote:

Another option is the 300 f/4 L IS
(advantage over the 400 is IS), and a 1.4x TC. I use that
and it is much sharper than my 100-400.

About the same, here. It seems my 300 is about 320 and my -400 is about
360, so the 300+TCcombo actually has a narrower FOV.
--


John P Sheehy