Ckw From UK - England, joined Aug 2010, 769 posts, RR: 16
Reply 1, posted (11 years 1 month 1 week 5 days 13 hours ago) and read 1370 times:
I use both the 1.4x and 2x with my 70-200 f2.8 + 300mm f4. Love them. With the 70-200 f4L quality will still be up to the standard of many 3rd party zooms. You would retain AF with the 1.4 (effective f5.6) but loose it with the 2x (effectively f8) - however the 70-200 is an easy lens to focus manually.
You can check out my pics if you like, plenty of telecon examples (I was recently emailed to ask if I ever shoot without convertors )