GuyF said:
Cough, splutter, facts?? Whatever made you think we would recognise or accept fact over speculation, hearsay, rumour, misguided opinion and blatant lies? You're on the wrong site if you want to cloud debate with your facts.
So what are the facts?
1) 3 separate companies make an announcement on the same day regarding the use of lenses on the 5Ds & 5DsR
2) Sigma & Tamron mention that firmware updates are required
3) Various currently available lenses that are being made by Canon (including well regarded ones) are not on the list
That's where the facts end as nobody has said anything in detail about why the updates are required or what the qualification was for putting the list together, nor that there are any errors in that list.
Now onto trying to draw some logic from all of this...
Is (1) a coincidence? I doubt it. Doesn't pass the smell test.
(2) implies that the issue is not around optical quality (especially since it is specific serial numbers in some cases)
(3) also tells us that whatever the issue is, it has nothing to do with optical performance.
There is a chance that some parts of (3) are just clerical error (such as the list being put together before the 50/1.8 IS STM was released and nobody thought to include it.)
Going further and trying to make educated guesses...
So what is it about a lens that could require an update to the firmware? The protocol used by the camera to communicate with lenses is one possibility. The identifiers that 3rd party lenses use to identify to the camera is another.
Maybe it is voltage levels or timings used by the newer cameras to communicate with lenses?
The increased pixel density might put a higher strain on IS capability in some lenses but then why hasn't this been declared and issue with earlier cameras of similar pixel density?