Originally posted by AfterPentax Mark II
it also means that manufacturers of camera's and lenses have to share their secrets () about how the camera or lens works to get optimum results with the lenses (and other accessories such as flash)
Some manufacturers like Nikon keep their mount information close. Others like Sony open up their standard. That has not stopped Tokina, Tamron, Sigma from making excellent products for many years.
As for flash, that's unrelated to lenses, and again third-party manufacturers have worked around that for years.
Some manufacturers like Godox have even pushed things far enough to create triggers that are compatible between brands. With the right receiver, you can use, say, a Nikon flash with a Pentax camera, remotely, with full TTL.