The Dall Null is a great test for high f/# mirrors like your 10" f/10. It fails miserably for that 16" f/4.5. You've got to be on-axis like a Ross or other null lens test for that one. You've got the OSLO file now, try it for yourself!
Yes, I was pretty sure from the literature that the larger short focus mirrors under test show astigmatism from the lateral separation in the standard Dall test.
I was interested in looking at a beam splitter to avoid this, or otherwise look at solutions for the off axis issue. I had considered making a Dall Null unit that could be dialed in...like the barrel on a camera lens focus...to set separation from the integral source for various optics/conics. A laser diode for the source....it would be easy to set up and do Null figuring.
Question: in your *.len file, I notice you had worked "reverse" in setup....source, mirror, then lens, then KE? It does give a 1/30 wave null, but how else could it be set up...i.e. the usual source, lens mirror then KE?
I'm working on it.
Edited by ccaissie, 30 June 2022 - 09:21 AM.