To get a 55mm backfocus:
1.Use your ASI 715 MC (backfocus = 17.5mm).
2.Add the ZWO Mini filter wheel (thickness = 20mm).
3.Add an additional 17.5mm spacer between the filter wheel and the coma corrector.
Once you have the correct spacer, you should be able to achieve the ideal backfocus and capture clear, coma-free images with your 150/600 Quattro.
