1400mm ?? Ok i guess your taking into consideration the 1.6 crop factor am i right ?
I was looking at something that gives me between 500-800mm. Maybe for some wildlife shots. Never assume why one would need such a long range hmmm. There are some subjects, such as waterfalls etc which are far away and i wish i had more zoom range on those subjects.
If i put a 2x extender (you meant an extension tube right ?) on my 55-250 IS will the sharpness quality take a hit, also will AF and Aperture control etc work ?