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Thread: More Coma Corrector troubleshooting

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    Default More Coma Corrector troubleshooting



    I continue to work on what seems to be a lack of "squareness" in my imaging train since the coma corrector was introduced. My most recent examinations picked up a few things:

    • One of the nuts that holds the focuser to the OTA was loose
    • The focuser itself seems rock solid but
    • I haven't been tightening the focus lock knob as tight as it will go, in fear of shifting the focus when I do. I am reconsidering that behavior
    • there is a tiny bit of slop in the t-ring connection to the camera - I ordered a Blue Fireball t-ring today to address that
    • the Baader spacer I put in couldn't mate up to components on either side, adding about 3mm to the back spacing. This was because the threads on the Baader were longer than the other components could take. A Blue Fireball spacer has arrived and fits much closer (+/- 1mm) than the Baader (+ 4mm)


    I also mentioned I was going to check my images to see if the stars were stretched along the RA or Dec axis. I found the initial run in May they were not, and they were much rounder than my two June efforts. Both of those showed drift aligned with the RA axis, indicating some sort of guiding issue was added to the mix. The May session was done with my old PC running PHD2 2.6.1, The June session used the new laptop running PHD2 2.6.3. Coincidence? Probably not. 2.6.3 has a new parm in the Calculation module that reads the scope declination from the mount. Since my guidescope and imaging scopes are not aligned exactly I am wondering if that might have an impact.

    I am awaiting the T-ring. In the meantime, if I get some clear skies I will trying to fine tune the guiding (again).

    As always any thoughts and observations are appreciated. I am trying to not let this thing devour me, but I am getting closer to ordering a 2" t-adapter to go with the ring and resume straight prime focus photography, coma and all!

    Bob
    Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Orion SSAG
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    Default Re: More Coma Corrector troubleshooting

    Bob check your inbox my lensfriend. I noticed some tilt from my recent tests using my Newt with the GSO LB focuser. Really tight stars in just one corner and the other 3 a bit questionable suggesting tilt in the optical path somewhere. Inside on the bench watching the entire focuser rig I noticed it moving as I tightened and untightened the 2 lock thumbscrews. The shift of the 2 thumbscrew design is the weak link of it I believe. I ordered a Hotoch SCA self centering T- adapter to bypass the barrel's two thumbscrews and compression ring design to test this theory. I'd give yours a close look as well.
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    Default Re: More Coma Corrector troubleshooting

    Quote Originally Posted by Leveye View Post
    Bob check your inbox my lensfriend. I noticed some tilt from my recent tests using my Newt with the GSO LB focuser. Really tight stars in just one corner and the other 3 a bit questionable suggesting tilt in the optical path somewhere. Inside on the bench watching the entire focuser rig I noticed it moving as I tightened and untightened the 2 lock thumbscrews. The shift of the 2 thumbscrew design is the weak link of it I believe. I ordered a Hotoch SCA self centering T- adapter to bypass the barrel's two thumbscrews and compression ring design to test this theory. I'd give yours a close look as well.
    Thanks, Chris. I have never (even when i was a kid) understood how people who are clever enough to design and build scope optics to such fine tolerances are unable to grasp the flaws in attaching anything to it with two thumbscrews! I will check this out on mine.

    I've said it before, I hate that there is no ability to screw the coma corrector onto the drawtube - seems like such a simple and important concept to me. Rant over

    Bob
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    Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Orion SSAG
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    Default Re: More Coma Corrector troubleshooting

    Quote Originally Posted by bobharmony View Post
    I have never (even when i was a kid) understood how people who are clever enough to design and build scope optics to such fine tolerances are unable to grasp the flaws in attaching anything to it with two thumbscrews!
    "But that's the way we've always done it."
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    Dave Hunt
    Scope: Celestron C6-N
    Mount: Celestron AVX
    Camera: ASI1600MM-cool,SSAG,Canon 1100D (T3)

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