Canon Extender EF 1.4x III Review -

RS_RS wrote:

The PROS:
* Excellent image quality.
* Can be used as a Manual Focus Only tool with compatible lenses.
* Sharper than the EF 2x III extender (which is slightly softer).
* Lightweight and easily carried.
* Matches the stark-White tone of the newer white Canon L-Series lenses.
* Extremely well built.
* More robust (more lock-down assembly screws!) than previous versions.
* Increases the focal length of the lens used by 1.4x
* EF 1.4x III matches the White-tone of the newer L-series lenses.
* Electronic contacts transfer lens information to the camera.
* Image Stabilization still works with compatible lenses.
* In-Camera lens correction recognizes Extender when matched to specific lenses.

* With certain recent bodies and lenses, activates more AF points at f/8 than default f/8 coverage. For example, with 100~400 II on 5D Mark IV and 80D. This is a really significant benefit.

That's correct - I missed that one.  Thanks for adding. It's a very important Pro.

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The CONS:
* Not inexpensive.
* Only works with SOME lenses (Telephoto).
* Can no longer be stacked with EF 2x III without a 'spacer'.

This is not the fault of the 1.4× III but of the 2× III. You can stack the 1.4× III with the 2× II.

You can - and they ought to fit... but the EF 2x Mk II has noticeably inferior optical quality compared to the EF 2x Mk III... so I'm not sure why anyone would want to do this.  I'm tempted to buy the 2x III and was just looking at one today.  I probably Just need something to motivate me to drop the cash.