We've decided to make some further modifications to the steering wheel part of the M4 mount, but before taking it down to Cape Town, we spent a full day doing a trial alignment of M4 to M5.
The procedure involved finding the minimum coma position for the pinhole, then moving it off axis in X by +/- 1.5 & 1.0 mm & making wavefront measurements. Plotting the Z6 values (one of the astigmatism Zernikes) as a function of the X-offset allowed us to iteratively adjust M4 in X decentre (aiming to find a symmetrical Z6 minimum). When we could make no further improvements with X decentre, M4 was iteratively tilted in X to minimise the coma again. Next we repeated the whole procedure in the Y direction, obtaining better Z6 vs Y-offset curves & again minimising coma. A final pinhole scan in the X direction yielded the vastly better pink Z6 curve in the image below - the technique works beautifully! :)
Once we got over that excitement, it was time to remove M4 & detach it from the ring that's going home with us tomorrow. Therewith my best M4 photo-op so far!
Without its ring, we had to figure out a new secure way to store M4 - 'n boer maak a plan as they say in Afrikaans. Although in this case the boer's an Irishman, but that's OK... he's one of us Africans now ;)
Off for a week now while the SALT Board Meeting takes place in Cape Town, we'll return on Monday the 9th!