I just received mine today, still waiting the adapter from fotodiox but already did some handheld tests
its bigger than I thought
First, the magnification it gives: full zoom without and with the TC
I noticed the focus tends to hunt more with the TC on, if focusing the bird instead of branches was hard, with the TC it will be even harder, gotta try it in the field
Also, didnt noticed loss of light and the DOF got smaller, which is cool
Now IQ wise, I had some surprises
here is a 100% crop with the TC vs upsized image
Where did the red fringe go? shouldnt the TC magnify it as well?? I was expecting more artefacts, not less... I must have gotten a miraculous TC...
About the IQ, id say only pixel peepers would notice the diferrence in this comparision... at least while using low ISO an upsized must be pretty close to the TC, I used ISO200 on this test, it looks bad cause the noise is also upsized
100% crops without and with the TC
Again! The TC shot doesnt have the red fringe that the first picture has
also it shows a lot more of crisp texture on the box
Well Im happy with it

_________________
Canon 450D, S5 IS and A510
photographic blog