I don't really know anything about (semi-)professional photography, but I always assumed objectives from different manufacturers were compatible. Can't you use your old glass with the new, different camera?
Just as a bit of additional background modern lenses and flashes may do a bit more than you'd imagine. I'm a Canon user but say I attach a 70-200 zoom lens the auto-focus motor is in the lens so if say tracking a moving vehicle in servo mode there's a constant stream of information flowing between the camera and lens to try and hold it in focus. The current focal length also gets reported back as I zoom in and out, and if a compatible flash is attached it will mechanically move reflectors to direct the most flash power into a smaller area that will still cover the scene.
Those are proprietory protocols but have been reverse-engineered by 3rd party lens manufacturers. Occasionally though the OEM will begin using some new feature / protocol that was always present in their lenses and it's not uncommon to hear that a 3rd party lens needs to go back to the factory for a firmware update to work with a newly released camera.