Dear fellow Alpy users, please see my post #41
Everything In my Alpy is screwed down tight as far as I can tell. Yet I am getting these large disparities in the calibration of H alpha.
It suggests something does change when the instrument moves from one star to another, i thought of checking the Relco bulb isn’t loose, presumably the grism is unlikely to move as it’s held in place by a spring.
The best calibration using the lamp lines occurred when there was a meridian flip between the target and the acquisition of the lamp lines.