Hi All, this is my first post here but I've been lurking this forum since years!
I have a TSA102 triplet and when looking at a very bright star at high power (230x, no diagonal) in good seeing I notice that, in-focus, the airy disk appears sharp but the diffraction pattern is slightly but obviously skewed to the left: the diffraction rings look brighter and "more present" in that direction than in the opposite one. Moreover, if the star is of medium magnitude (i.e. not overly bright) the first diffraction ring appears "C shaped" around the left portion of the airy disk, rather than circular. If I turn the tube 180° in its cradle, I observe the same behavior but reversed (rings brighter on the right portion of the star).
As for the out-of-focus pattern, I see similar figures inside and outside focus, with apparently concentric Fresnel rings. Outside focus pattern looks sligthly sharper.
I also tried putting a Cheshire eyepiece in the focuser: the green reflections appeared concentric but they looked best (sharpest) if I kept my eye sligthly off-axis. If my eye is perfectly on-axis, the central darker spot looks sligthly blurred and not perfectly black and sharp as it appears with my eye off-axis.
This makes me think of possible miscollimation of the scope. Unfortunately, these scopes do not have collimation screws and I don't know what to do...
Could you help me diagnose the possible issue?
Edited by RichardZ, 30 June 2020 - 07:59 AM.