Wow. There is a big difference between your (Canadian/International?) Samyang/Rokinon 135/2 vs mine (US?) one. Take a look at your first photo (the one with the ZWO EAF in the background).
Now look at this photo that I just took of the Rokinon 135/T2.2 together with the shell of my "learning" Samyang 135. Do you see something weird?
If not, take a look at the distance scale of your Rokinon and the distance scales of my two lenses. Yours are reversed! Is this a Nikon/EOS difference (like the way Nikon uses a left handed bayonet twist vs right handed twist for the EOS and Sony F/FE)?
FWIW, all of my lenses, manufactured by Canon and Sony, have the same clockwise/anticlockwise focusing as my Samyang and Rokinon.
Even my Sigma 40, which has the Nikon bayonet, has the same distance scale orientation:
BTW, see the infinity mark on the Sigma? That was where it landed after I had finish tuning for best backfocus and tilt.
The Sigma infinity mark was really smack on, and I did not purposely try to focus it that way. That is where the ASIAIR autofocus placed it after I had adjusted for best tilt and backfocus.
For my future tunings, I am going to first guide the helical focuser to the inifinity mark and keep it there, adjusting only the backfocus spacing and tilt to maintain sharp focus :-). And once I get tilt moderately under control, to just use the ASIAIR autofocus.
I am starting to understand now when ASIAIR autofocus works, and when it does not work.
Basically, the ASIAIR picks different stars as it gets in and out of focus to create the U curve. The ASIAIR autofocus does not work when there is tilt, or if the image plane is not flat since it is measuring stars that inherently focus differently. Once every star in the frame has the same focus on the image plane, the ASIAIR autofocus works very well -- better than a Bahtinov mask, unless you have a good glass mask and measure the spikes very carefully.
But this means that most of the unwashed, using imperfect OTAs and had not bothered to tune their tilt and backfocus perfectly (and I mean HFD/FWHM that deviates no more than 0.5 to 1 percent across the entire FOV) will not get good focus. Tilt and backfocus needs much better than 1mm type accuracy (and with short focal length lens, needs better), and I don't think most ZWO customers have the tools to do that. If they are so cheap as to choose ZWO products over better products that cost a bit more, they are not going to spend money on tools like the Askar backfocus adjuster. Those who use SCTs are in a hopeless situation since I have never seen an SCT able to get image plane flatness.
Yeah, that center line on the cheap tripod ring is way off :-). China really needs Ed Deming.
Chen
