I have ordered a 300mm f4 and am planning to extend its reach when necessary using a 1.4 extender. However I am not sure if the mk 3 version is worth the extra cost. I can buy a used mk 2 extender for around half the cost of a new mark 3. Do you have any thoughts Bob? Ken
I'd probably go for the MkII at half price myself. In fact I'm still using my MkI extenders. I did test the MkII against the MkI on the 300/4L and found little difference, certainly not enough to make me switch from the MkI to the MkII. I haven't tested the MkIII extenders, but I again I doubt that they are significantly better.
The latest extenders are supposed to have better contrast and maybe better AF and sharpness, but on a 300/4 I don't think you'll see too much difference. It's said that with the 2x extenders, the new MkIII version is a step up from the MkII, but I've never tested it myself.
I have a 70-200 f/2.8 L IS w/ Mk II extender, and not long ago I borrowed a 300mm f/4 for a Baseball Game shoot 1. The 300 f/4 is a REALLY nice lens which focused blazingly fast on both a 1 Ds III & 7D and produced VERY sharp pictures. 2. with the 1.4 mk II I noticed no practical difference in either focus speed or sharpness.
This was obviously not a critical lens test,and I had good light, but in this practical use I thought both lens and converter performed flawlessly. Good luck and enjoy the lens.