Primes for wildlife ...

[Loswr]

Interesting! I have a 1.4xIII and a 2xII. Does using an extension tube make any difference to function, e.g. losing infinity focus?

Yes, it does mean loss of infinity focus, although you can still focus out quite a distance.

Since you have a 500 II, the 2xIII would be a good addition (except for the no stacking part). AF performance is better with the 2xIII, and the optical performance is better, too (the reason the 1.4x won't fit in the back of the 2xIII is that it has 2 extra elements compared to the 2xII (9 vs. 7).

 

[scyrene]

Since you have a 500 II, the 2xIII would be a good addition (except for the no stacking part). AF performance is better with the 2xIII, and the optical performance is better, too (the reason the 1.4x won't fit in the back of the 2xIII is that it has 2 extra elements compared to the 2xII (9 vs. 7).

Thanks for the info!

You're right, but I'm afraid it's far down the list of priorities. I could sell the mark II and recoup most of the cost of the new version, but I rather like the idea of keeping both, so it'll have to wait until after my next big lens purchase

 

[Skulker]

I also find stacking the extenders can produce usable images if I can't get closer, although this is manual focus only and works best with support.

Just a side note on this, you cannot stack the Canon 1.4xIII and 2xIII extenders together, unless you use a small (e.g. 12mm) extension tube between them. The MkII extenders can be stacked, and 1.4xIII can be mounted behind a 2xII.

Interesting! I have a 1.4xIII and a 2xII. Does using an extension tube make any difference to function, e.g. losing infinity focus?

I've taken shots of the moon with stacked 1.4x and 2x converters separated with a 12mm extension and a 300mm f2.8. I used live view. But of course the moon is moving quite fast with that sort of magnification.

I think infinity focus may depend on the manufacture of the lens. Clearly it should theoretically loose infinity focus, and I haven't looked to see why it worked for me.

With a good stable tripod or rest this combination can work.