The fasting of the 250° lens to the body might require a bit more force than usual. Make sure to go this way:
- Detach the lens from the camera
- Screw the red rig to the lens as tight as possible (no space between lens and red ring)
- Mount the lens to the camera body, screw it carefully so that the lens does not touch the sensor.
- Turn on the camera viewer.
- Close the distance between lens and sensor by continuing screwing the red ring. Be careful, since the lens may touch the sensor. Note, that the red ring sits very tight in the thread.
- As soon as the focus is set, you can use the hexagonal bolt to fixate the lens.
Admittedly, it’s a bit special workflow, but it should work this way.