Originally posted by Ian Stuart Forsyth I suspect that you would have a little better performance when that TC was dedicated to a set of lenses
I'm pretty sure that is the case, because light is projected differently (different angle) onto the sensor , depending on lens design. So the optimal TC optic is designed to be a continuation of the lens optic.
I used the Pentax HD DA TC with the DA 300 and it worked very well. I sold the DA300 and bought the 150-450, I still had the TC , used it for a while with the 150-450, I compared apsc crops to full frame + the HD TC and I decided to sell the TC.
The decision to sell the TC was easy. With apsc crop I got double the frame rate, no vignetting and better sharpness. Plus I got the money from selling the TC. If I wanted more "reach" out of the DFA150450, I'd use a Pentax K3 Mk III instead of a DA TC.
FF TC for the 150-450 or 70-200 2.8, yes I'm all for it.