Corona camera has option to set DOF by object, however it will set focus point at selected object’s pivot point - that’s not always what we want. Therefore it’s recommend to create dummy helper and use it as a focus point holder. You can precisely control that dummy’s position with 3ds max’s select and place tool.
Or
- Be sure to have viewport clipping off
- Enable camera clipping plane(s)
- change clipping plane so that it clips your desired DOF point
- copy that value to focus distance (and disable clipping planes again)
Or
Your could use this script: https://forum.corona-renderer.com/ Autofocus
Good Luck