After further testing, Sigma has concluded both autofocus and optical image stabilization (for applicable lenses) work 'without any issues' on the following lenses when used with Canon EOS R mirrorless cameras via the EF-EOS R mount adapter or Control Ring EF-EOS R mount adapter: DG Lens - SIGMA 12-24mm F4 DG HSM | Art
Build Quality and Handling. Like the rest of Sony’s GM lens lineup, the Sony FE 2x Teleconverter is well-built with a magnesium-alloy barrel and metal lens mount. You might think that the teleconverter would be relatively hefty given the optical design which features 8 elements including one aspherical element, but it’s incredibly light at
I don't have an EF 500mm f/4 mk II lens on hand but there have been improvements to the results from the EF 1.4x III Extender. It is claimed that the microprocessor in the EF 1.4x III Extender promises faster AF speed and increased AF precision on the Canon EF 500mm f/4L IS II USM Lens. So yes, you should see an improvement with this lens.

WaddizzleLegend. 11-05-2020 09:57 AM. If you want a teleconverter for an EF mount lens, then you must use a teleconverter for an EF mount lens. If you wish to. Use an EF mount lens on an RF mount body, then you must use an EF-RF mount adapter. I am not aware of a single device that can do both functions.

I have been using the 1.4x extender with various models of the 70-200 f/2.8 along with other telephotos for 25 years. I love the 1.4x and hate the 2x. I have seen almost negligible change to an image with the 1.4x on an L lens and no difference in autofocus speed.
600-1,000mm f/11-14. Canon RF 70-200mm f/2.8 IS USM. Not compatible. Not compatible. Canon RF 28-70mm F2 L USM. Not compatible. Not compatible. While it’s obviously disappointing that the 70-200mm won’t work at all with the teleconverters, and the 100-500mm only half works, both the 600mm and 800mm primes are fully compatible – and the
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canon extender ef 1.4 x ii lens compatibility