2 x extender autofocus

[BryanShaw1]

I have just purchased a used Canon 2 x extender II.

When fitted to my 7D, the Q screen automatically changes to MF MANUAL FOCUS.

Is the extender faulty?

[Waddizzle]

No, it is not faulty. The 2x extenders do not work with, or allow for autofocus, with any and all combinations of cameras and lenses.

[kvbarkley]

More importantly, which lens do you have?

[wq9nsc]

The 7D AF system won't work if the combined lens plus 2X aperture is above f5.6.  So unless you are using a f2.8 or faster lens, the 2X will put your 7D out of AF range.  A lens with a maximum aperture of f4 combined with a 1.4X will autofocus with your 7D because the one stop loss from the 1.4X results in a f5.6 combo.  The same f4 plus 2X results in a 2 stop loss of aperture putting the 7D out of its AF capable range.

Even with the sharpest primes I own (EF 200 f2, EF 300 and 400 f2.8), results with the 2X converter are most underwhelming.  With the sharp primes, the image looks OK until you compare and see how much IQ degradation occurs compared to the bare lens.  With lesser glass, the results will be even less impressive.

The 1.4X does work quite well with many lenses and as long as the bare lens is f4 or faster, it will AF with your 7D.

The 1 series will AF with aperture combinations as slow as f8 but even with my 1DX III the AF is noticeably slower and less sure with this combination (i.e. using an EF 800 f5.6 with the 1.4X which results in f8 combined and it will AF but nothing like the lightning quick results with the bare lens).

Rodger

[BryanShaw1]

The lens is the EF 100-400  L IS.

Without the extender the autofocus options in the Q menu are all operational. When the extender is fitted it only shows a green box MF. Pressing the set button twice turns the box blue but still shows MF. (I'm trying to give as much info here as possible)

I know that AF is hit and miss with extenders but It's as if it's somehow switched off - there is nothing there at all, whatever the apperture.

[ebiggs1]

"The lens is the EF 100-400  L IS."

The 2x tel-con is not compatible with that lens. AF is possible only with a lens that has an f2.8 or faster maximum aperture. Your lens is a f5.6.

[wq9nsc]

With the 2X extender in place, even a 1DX III will not AF with using the normal AF system with that particular lens.  With your 7D, AF won't work with the 1.4X either because the aperture rises beyond the f5.6 capability of the 7D as soon as you add an extender.  Once your 100-400 is zoomed out to the f5.6 region, it is at the aperture limit of the 7D.

Your 7D turns off the AF function when you add the extender because the camera knows that its AF system won't work with that lens/extender combination.

I have never used live view with a 7D so I don't know what AF capabilities it has in live view.  It MIGHT work in live view with that combination but it will work very slowly.

Rodger

[BryanShaw1]

would the combination work with a EOS R?

[ebiggs1]

It will not even mount with out an adapter. 

[ebiggs1]

The bottom line is it is not a good idea with such a slow lens. Plus a lens that doesn't have the IQ, in the first place, to give up to the tel-con even if you could get it to work.