SolarChat!

Temperature around 7 ℃, Sun at 16 degrees, poor seeing — but sufficient to test my new adapter: M35x0.5 (male)/T2 (female), thanks to which I can now replace the drooping stock focuser with my Borg T2 helical. Since it has just 10 mm travel, I have to add/remove T2 extenders when changing from eyepiece to camera, but it's not a big problem. The Borg moves much more smoothly too.

Eyepiece setup (for Antares 9 mm ortho):
Camera setup (PGR Chameleon 3 mono with a custom T2/C-mount rotating adapter):
With everything rigidly connected I could now asses the sweetspot's position. Turns out it's just a bit off-center (either due to alignment of etalon assembly's elements, the diagonal's mirror or minimal droop in the Borg), but not preventing to get the full disc on-band. Single frame:
(note that darkening on the left is due to slight vignetting by B600, which is about the size of my sensor).

Stacks (processed in ImPPG):
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Excellent mod! M35 - hmmmm, that sounds the same as the thread on the back of the Quark, be interesting to compare...

I'm also interested in mounting the Borg focuser.
Can you say where you got the adaptor from?

Made to order by our well-known astromachinist (for ~€15; black-anodized aluminium with internal grooving against reflections). I guess you could find some local workshop to make a similar one (if you'd like to try my guy, here's the website).

Thank you for the information. So it is not a standard part beeing on stock somewhere.
I think I'm going to contact your friend in Krakow the next days. Unfortunately it is a bit far. I travel quite often to Poland but always into the north.

Torsten

My local dealer fabricated an adapter for me. I got everything last weekend.

Thank you very much for this great "research", it works very well.
The whole system is much mor stable, now. After this modification I'm able to center the sun and position the sweetspot. When mounting the camera afterwards, the sun is almost in the center of the chip.