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| p.5 #1 · 800mm f/5.6 + 1D-X + 1.4x Extender = Apparently It Can AF! |
I am surprised that to the best of my knowledge nobody has confirmed that finding of A.Morris ? I can not do it because I ain't got the Kenko converter, and I do not need it either, certainly not for the 800L. I suspect a few other 1DX/800L owners are in the same boat as I.
It is now confirmed. It's relates to the DGX TC. Look here:
This makes sense based on my past experience with the Kenko Teleplus Pro DGX series. I own the Canon 2x II, the Kenko DGX 2X and the older DG version. My tests were with the Canon 70-200 f/4L USM Lens
The DG version would disable autofocus on my 7D (but not my 1D Mark II as you'd expect)
The DGX version would not disable autofocus on my 7D, would report the correct aperture to the camera and the EXIF data was correct (f/8) but required me to set EC to -2
I've come to believe that the DGX teleconverters do not disable autofocus but when used with some lenses designed to be used with teleconverters they require EC to be set to 1 or 2 stops depending on whether it's a 1.4x or 2x converter. It almost seems as though the camera double counts the teleconverter and over compensates in metering. This does not seem to be the case when used with my Canon 135 f/2 however.
When I used the DGX versions with lenses that are not designed to be used with teleconverters (My 85mm f/1.8 + Kenko 1.4x is really quite good) no EC is required to get correct metering.
My tests this morning with my 5D Mark III also showed no problem with autofocusing at f/8. I was using a Sigma 70-200 f/2.8 plus a 1.4x and 2x Kenko teleconverters. The number of points accessible to me was less than the regular 61 but the camera was able to autofocus quite accurately. The speed was not as good as just the lens itself. I also tried my Canon 135 f/2 with the Kenko 1.4x and it functioned exactly as you'd expect.