Considering adding Canon EF 1.4x to my 70-200 f/2.8. Which one?

[Canon Man]

Is there a huge difference between Mk I, II and III? I know that my lens is not weather-sealed but with the way it's build I wouldn't care going under a light rain. Thanks.

 

[soylentgreen]

If you have the EF 70-200 f/2.8L, it should be weather sealed. Not monsoon sealed, but a good dousing should not affect it. In either case, I would hold out for the Mk III version due to some perceived improvements in AF and IQ.

 

[Overread20]

The M1 teleconverters are a grade below the MII and to be honest I would not consider going for an M1 teleconverter. The MII make a good improvement over them and are readily availible on the market both new and second hand.

The MIII 1.4TC is a slightly different story in that it makes only a minor improvement over the MII in image quality terms, a difference mostly seen in the edges of the shot and thus more evident on fullframe camera bodies rather than crop sensor ones. It is an upgrade, but at twice the price or more than the MII for many its not an increase worth the cost. Note that the AF speed bonus is listed as only affecting the new MII telephoto prime lenses (eg 300mm f2.8 IS L MII and longer)
So I'd say go for an MII, whilst if you feel richer, want the best there currently is or are looking toward a future fullframe camera - then the MIII.