Lens calibration with an Extender

Having recently purchased the 70-200L IS ii and the x2 Extender, I calibrated the focus using the excellent DotTune method described elsewhere.

The lens alone is excellent but, and it is early days I must admit, the results with the Extender have not been very good. (This may at this early stage be me).

However, having calibrated the lens, should I now calibrate the lens/Extender combination, and if I do will the camera (7d) keep seperate data on the lens and lens/Extender combo?

AF calibration data is stored separately for a lens alone vs. that lens in combination with an extender, yes. So if calibration is needed with the extender too, then you have to do that as well.

Yes,

Realise that a further calibration may be required, just concerned that the camera would record it as a different 'lens' from the lens without the Extender.

I just checked on my 7D and lens + TC does register separately from lens alone. So, yes, if you wish you can MFA the combo alone. (Note: I was using 1.4X II and 300/4 IS, instead of the combo you are using.... but I imagine it's the same.)

Frankly, a 2X on a zoom will cost you some image quality, even if you MFA it perfectly. You might look for sample images from others using the combo to see if yours are comparable. Then you can decide whether or not it's acceptible to you.

Thanks for that amfoto, I'll probably go ahead and do it - as much out of curiosity as anything. Tegarding IQ with 2X, I have seen some pretty impressive results and little change in image quality is claimed.
I think a lot of the 'change' in IQ is because of the increase in skill level required when operating at the 400mm end of the range - especially with the 1.6 crop.

An extender magnifies everything it sees, also imperfections within the lens it's mounted upon. But the EF 70-200 mm f/2.8L IS II USM is a very good lens to begin with. I've used it with the EF Extender 1.4X III quite a lot, on a 7D, as an alternative to also hauling the EF 100-400 mm f/4.5-5.6L IS USM on long walks.
Putting the extender on the 70-200 mm works notiecably better than putting it on the 100-400. I've had some fuzzy results from the latter combination, at least on the 7D. It looks better on the 1DX, but I haven't had any real chance to evaluate that yet. At least you do get AF to work with that combo on the 1DX.

The fact that calibrations of lens and extender pairs are stored separately in the camera is mentioned in the user's manual.

Ah, the User's Manual. Whoever would have thought!

Yes, the AF works but I think a little slower though once again, early days for me.