There are adapters and then there are adapters. Adapters between different brands often rely on reverse engineering and there's no guarantee of future compatibility. I have nothing against reverse engineering, but it does come with risks, including one side deliberately breaking it.
If Canon changes the EF-mount protocol then they need to issue firmware upgrades to every EF-mount camera that has been made since 1987. Doesn't sound reasonable. Older bodys might not even be possible to upgrade without being sent in. Sound like a support nightmare.
Also the reverse engineering people are fairly good at figuring things out so it wouldn't probably take long before they know the change made, and the adapters have firmware upgradability and the users of those are used to upgrade the adapters as well, since the development pace is high.
Adapters involving optical elements also introduce more glass into the light path, so more loss.
Those adapters are basically only used on crop sensors to boost light by using more of the otherwise lost image circle and when the flange to sensor distance is longer on the body it will be adapted to. So doesn't apply to mirrorless FF bodys with their short flange to sensor distance, adapters for those are all glass less inside.
That's not the case here. All three parts of the system (lens, adapter, and body) are under Canon's direct control, and the adapter itself is basically an extension tube (perhaps with protocol conversion that again is under Canon's control).
The Canon R bodys seems to be double protocol knowledgeable so they speak EF and RF protocol and switches between them depending on what lens it recognizes. So the adapters seems to just be electrically passing the signal through. That is well done by Canon. The RF protocol is faster with a higher clock frequency. One must remember that EF was made in 1987 so things have happened since then.
I'm not sure how Sony has implemented the A-mount protocol in the E-mount adapters, like the LA-EA3, meaning if it just passes through or translates. The LA-EA3 is like Canons RF adapters or Nikons Z adapter in that it only works with lenses with their own focusing motor. Canon has no lenses without motor, but Nikon has, and those users are left without auto focusing on the Z.
Canon has done a really good job of maintaining compatibility with older lenses, to boot.
Yes, and so has Nikon and Sony done as well, Sony even took care of the users that have lenses without focusing motor and supplies the LA-EA4 adapter which drives them. To be honest, the AF-module would gain from an update to the same one as in the A99II camera, or even better be driven by on sensor AF, but at least Sony has an working option for the old Minolta screw drive lenses etc. It will be interesting to see if Nikon will follow with an adapter like that one day.
But really, anyway you do it, adapters is still a plaster solution. It fixes the problem on the surface but not the root cause. Native lenses made for mirrorless will always be better.
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Best regards
/Anders
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