new tele extender on old lens?

HI,
I have been reading lots of positive reactions on the newest 2x TC III; it seems there is almost no IQ loss with this TC. I have an old 2x TC I but that is not very good as it distorts the corners, so I almost never use it. What would the effect be if one were to put a 2x TC III on a IS I lens? thanks!

IS I lens? Do you mean the 70-200 2.8 IS?

....or the version I IS tele-primes?

desperoadie wrote in post #15674569
HI,
I have been reading lots of positive reactions on the newest 2x TC III; it seems there is almost no IQ loss with this TC. I have an old 2x TC I but that is not very good as it distorts the corners, so I almost never use it. What would the effect be if one were to put a 2x TC III on a IS I lens? thanks!

"it seems there is almost no IQ loss with this TC" I would say that is a big exaggeration. While the 2x III does get better reviews than the 2x II, it still produces a noticeable degradation in Image Quality.

Which lens do you have? There are lots of lens plus 2x III comparison tests here:http://www.the-digital-picture.com …omp=0&FLIComp=7​&APIComp=2