Hi guys, Sorry for bothering you again with this subject, being a beginner I'm a bit of a numb skull. I have a sigma lens with a f5.6 what will the size be with a 1.4x converter . And the second question is I have a sigma lens with f6.3 what would the size be with a 1.4x converter. I don't want to pass f8 as I would loose auto focus. And I don't want to waste my money as I need it to be auto focus. Thank you all. Pete.