Kevin_A Here are the low rez images due to zwo site limitations to file sizes.
Wow, looks like you have more work to do on tilt than my Pleiades:
BTW, your small pixel camera shows (stars with HFD of about 4 pixels at the center). I wish the IMX571 had smaller pixels for us small focal length scope users. Oh, the RST135 with encoder still needs to be autoguided with the focal length of the P-68; very visible elongated stars with the +/- 2.5 arcsecond Renishaw encoder, with the plate scale of the IMX571. The Sigma 40mm probably won't need to be autoguided with that mount.
I noticed something I am not used to with the Pleiades... the focus at the corner is much more critical than at the corners. To the point where an adjustment of just 5 EAF steps shows coma changes at the corners (and this is with the EAF connected to the fine focus shaft of the WO), while the scope shows no visible focus shift with a star at the center even with 30 to 40 focus steps.
So I have been roughly focusing at the center and then go to a corner and start adjusting focus by 5 EAF steps at a time -- to look at the coma. Then change the backfocus adjuster, and rinse and repeat.
The miscentering of my spot diagram between the red versus blue wavelengths is still worse than what WO publishes, though.
This is what WO shows for about APS-C corner (about 14mm from optical axis). The square is 100 nm (unlike Askar, who cheats and uses a 200nm x 200nm square to make their scopes appear better to the unwashed. Tak uses 100 x 100 nm too. I am starting to trust WO more, and Askar less (well, I have never really trusted Askars and Sharpstars).
Heck, a Baader Semi-APO would probably remove that magenta shift :-).
For now, the Rokinon looks all properly mounted now. Don't know if it is clear enough to test it tonight, though.
Next thing to do is to now tweak the Rokinon's base plate for the Sigma 40mm. I am interested in what that lens can do, but want a reasonable mounting first.
I suspect that I wil be using the Pleiades more though. The focal length is at a sweet spot for non-wide field (not my focus in a Bortle 5/6 area), while the speed is good; albeit with my particular Pleiades focal length, it is really f/4 and not f/3.8.
