I actually have 3 questions, related to this topic:
1) Do third party manufacturers like Sigma/Tamron/Tokina license the right to develop for Nikon/Canon mounts? I've heard people say they do, and others say that they reverse engineer compatibility.
2) If the latter is true (reverse engineered compatibility), then what makes 3rd party lenses legal? It seems like if Nikon/Canon is purposely trying to block development on their mounts, then they should be able to go after these companies for something...
3) Why do third party lenses have compatibility problems with some newer bodies? (e.g. Sigma with Nikon D5300/Df) I am confused, because this situation doesn't make sense. If Nikon/Canon has some secret encrypted firmware code which still allows old 1st party lenses to work, then why don't they just completely block 3rd party lenses from working at all? If they don't have some mechanism like this, then logically the mounts are probably standardized (since very old lenses still work). Am I missing something?