For RED camera operation: 

Set eyepiece dioptar to your own eye.

Place the Luma Check into the optical block, turn on the LED lights of the   Luma Check  and focus on the cross hair.

Mount Luma Check on PL mount of camera.

Loosen the mount and rotate while looking through the Luma Check. When the sensor pixels are in focus lock the PL mount of the camera and you are done.