[mst]

[quote name='popo' timestamp='1312826616' post='10513']

That is my guess also. If you use a 1.4x on it, the focus range is limited to a shorter region than without, and the combination from memory is about 1:1 magnification at that point. I guess with a 2x they could have limited it further out again to maintain enough effective aperture, but for whatever reason they chose not to.

[/quote]



Thanks for the hint, I hadn't noticed this behaviour yet. I just tried it with the Sigma converters, and indeed the lens only focuses down to 0.5m with the 1.4 TC attached. That's exactly where the effective aperture jumps from f/5.6 to f/6.



You can of course focus closer manually. At MFD, the combination has an effective aperture of f/8 wide open (and for the record: f/11 with the 2x TC).



With the 2x TC, the lens should principally be able to AF from infinity down to 3m ... that's where the effective aperture decreases from f/5.6 (wide open) to f/6. No success, though, AF is nonfunctional with this TC, regardless of the focus distance.



-- Markus