Center a Object at hit.point in Camera

Hi,
i have a system to “grab” an object an drag it around.
But if i grab it at any point, it jumps at the center position in the camera.
i need to know how to grab the object without center the objects center into the camera.

Its hard to explain xD

Just save the offset to the center and add it every time you reposition the object due to dragging

Ok, but how can i do this?
i have this to move the object around

selectedObject.gameObject.transform.position = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance_to_screen));

i can get the Offset with hit.point - hit.collider.gameObject.transform.positon right?

but how can i put this offset into the movement?