This is an update on the testing of the TS 102mm ED f11.
The observing portion of the evening is discussed here:
viewtopic.php?f=6&t=11497
This post is to fulfill the promise of more detail on the testing of this scope.
My original plan was to use the Celestron NexYZ smartphone adapter to take photos of the ronchigram. Unfortunately, this did not work out. I foolishly tried this out at night violating my rule to never do that. By the clear light of day (see photo) it is obvious why this failed. Note the taper on the top of the grating eyepiece. How is a cell phone adapter going to secure stably to that?!
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This indicates that a new tester is needed. TS has a 10 line per mm tester so with flatter machining. It needs to be ordered.
So, having convinced myself that a real ronchigram was not possible, I fell back on visually inspecting the ronchi pattern. The instructions recommend using a 2nd magnitude star but I like more light and chose Altair. My procedure is to use the highest useful magnification eyepiece to get close to focus then slip in the Ronchi and refine focus, playing with it a bit.
My first tries where with the Stellar Vue 2” quartz diagonal in place. This tests the objective and diagonal combination and so is of some interest. When doing a ronchi evaluation it is important to remember to not just look at one orientation and declare victory. No indeed. One must remember the wisdom of the “Studebaker Hoch Dancing Lesson and Cosmic Prayer for Guidance” which advises: “Twirly, twirly, …., filmore, filmore….”. I rotated the Ronchi grating to rotate the pattern. There were deviations from perfection which I estimated to be about one tenth to one eighth wave in a zone occupying about a tenth of the image in the 5 o’clock direction of the field centered about half the radius out from the center. This is close to the specification of 1/10 wave for the diagonal alone. So now to diagnose whether it’s the scope or the diagonal. If it’s the diagonal I might consider taking a chance on an improvement.
Removing the diagonal I inserted 2 Astro Tech 50mm extension tubes to make up the difference in optical path length. I then refocused using the 5mm KK and then removed it and added the Ronchi grating playing with the focus adjustment. Again, with the twirly, twirly, this time the ronchi pattern had no deviations from perfection. The zone I had seen is attributable to the diagonal and the optics of the TS102mm ED are seen to be essentially perfect.
In fact the appearance of the ronchigram is favorable in comparison to that of the
SV ED80 Access. The latter has a Strehl of 0.991 but the ronchigram shows a tiny edge deviation in the last 1-2 mm. The
SV shows slightly less stray noise in the pattern though indicating somewhat smoother optical surfaces.
Comparing the Ronchi patterns the TS102 wins on spherical aberration but the SV80 wins on smooth optics. Both are in 1st place in my book.
More to come on the TS.
Now, about that diagonal.
I think both are about equally useful. The star test serves better for spherical aberration overall. Ronchi does better for surface roughness and zone issues. Both the nights for star testing and the Ronchi testing had very good seeing conditions. Only the Ronchi test revealed the zone problem with the diagonal. 
