New sigma 24-70 f2.8 + 2x TC

i just went and picked up my sigma 24-70 f2.8 EX DG macro
after playing with it a little while i stuck my sigma EX 2x TC on it and although it stops the lens from zooming any wider than about 68 mm it works meaning i have a 140mm f5.6 with a minimum focusing distance of about 20 cm

my question is - will this damage anything, it doesnt say anything about teleconverters in the instructions

Wow! how is IQ and AF speed? can you post a shot?

these are full frame images just resized - exif should still be available

taken using 350d and 580ex

AF isnt too bad, it hunts a bit in dim room light, should be fine outside
IQ is pretty good but the DOF is really thin in these shots (especially the eos 1 shot)

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Hard to judge IQ on these extreme closeups. But wonding 1.4x tc on this lens making 33-98mm f/4 lens can be useful in some situations. I think only Sigma TC's stop the lens to zoom at wide ends. Should be fine with Kenko TC's

yep , the kenko should be fine, the sigma locks the lens out at 70mm
i will try playing a bit more tommorow in the sunlight and see how it works in the real world.

I thought the Sigma TC reports the AV setting to the camera.