"Quite so.
IMHO, the use of any tel-con or x-tube is a bandaide fix for a problem that requires the proper lens alone.
I don't althgether afree. My 70-200mm f/2.8 tolerates the 1.4x III quite well, I think."
Perhaps acceptable, I freely admit. One of the very few lens combos I agree do work well with the 1.4x tel-con is the ef 70-200mm f2.8L.
Two things, though, the ef 70-200mm f2.8L has a lot of IQ it can afford to loose. Second did you take the same shot with, say, the ef 300mm f4L prime lens to compare? No, I didn't think so!
A tel-con may be the answer but it is never the best answer, IMHO, of course, as always. 
@ebiggs1 wrote:"Quite so.
IMHO, the use of any tel-con or x-tube is a bandaide fix for a problem that requires the proper lens alone.
I don't althgether afree. My 70-200mm f/2.8 tolerates the 1.4x III quite well, I think."
Perhaps acceptable, I freely admit. One of the very few lens combos I agree do work well with the 1.4x tel-con is the ef 70-200mm f2.8L.
Two things, though, the ef 70-200mm f2.8L has a lot of IQ it can afford to loose. Second did you take the same shot with, say, the ef 300mm f4L prime lens to compare? No, I didn't think so!
A tel-con may be the answer but it is never the best answer, IMHO, of course, as always.
Well, you knew the answer to that question, Ernie, because you know that I agree with your oft-stated opinion that modern zooms have relegated the prime lens to niche product status. 
Our household contains, IIRC, two prime lenses: my wife's EF-S 60mm macro (which she likes a lot) and a Sigma 30mm f/1.4 that I bought as a low-light lens for my XTi thirteen years ago and have almost never used.
