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CGEM Alignment Problems

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#1 abrock5

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Posted 30 January 2011 - 01:06 AM

My CGEM has performed flawlessly for over a year until a few weeks ago, when I started having problems aligning. When working properly, I used a 2+4 alignment. Each additional star during alignment was closer and closer to the center of my 12.5mm reticle eyepiece. In fact, the last star would often be dead center. After alignment, my goto's were spot on.

However, this all changed (seemingly for no reason) a few weeks ago. Now, all stars are WAY off, and they don't get any closer to center when I add calibration stars. My alignment stars are on the west of the meridian. Often, when I'm finished adding calibration stars from the east, when I try to slew to one of my original alignment stars on the west, it is further off than it started. This is REALLY frustrating, as any kind of ASPA is useless, and therefore imaging is out of the question. Before the problem started, I was using 6min exposures and not throwing any out.

I have tried all that I know to trouble shoot this. My date, time, location, and timezone are all correct. I have checked this about a million times. My mount is completely level. I have done 2 factory resets. I use a reticle eyepiece to center all of my alignment stars. When I add calibration stars, I try to keep them spread out. None of this has made the slightest difference. Even more weird, even with a completely garbage alignment, I was able to get the mount painstakingly polar aligned several days ago, and was able to keep 100% of 6 minute exposures over 2 hours! This makes me think that it is not a mechanical problem...

This is literally causing me to lose sleep, and has made me consider giving it all up. I have been doing everything the same as before (maybe even more carefully now), and the mount just won't point in the right direction!!!

Here's the last thing I can think of trying. In order to increase stability, I went from a foot mount on my 80mm EON to rings from ADM. If I remember correctly, this was right around the time the problems started. The rings are obviously a little larger than the OTA, and, despite my efforts to get the OTA aligned perfectly straight in the rings, I'm sure there is more cone error now than with the original foot mount. While I don't think there is a huge amount of cone error, could an increase in cone error cause ALL of my alignments to be off??? I thought the +4 calibration stars were supposed to take care of that...

Any suggestions??? I'm pretty desperate for help at this time. I really can't afford an expensive repair or Hypertune service. I know CGEM's have had their issues, but mine was absolutely perfect for the first almost-year-and-a-half of service. I would really appreciate any help.

#2 BlueGrass

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Posted 30 January 2011 - 01:20 AM

I'd suggest one thing right off the bat. Put the foot back on and re-try the alignment. If all is well, you've found your problem. I'm not sure how much having your OTA off axis in adjustable rings would affect the alignment. I'd also do a factory reset after remounting the foot before attempting an alignment. Good luck.

#3 Fred1

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Posted 30 January 2011 - 08:52 AM

Agree with Blue Grass. Go back to the set up that worked. Note also, that Celestron has a 2 year warranty, so if you're 18 months in, then I wouldn't spend too much more time trying to figure it out if after you go back to your "set up that worked" it still doesn't perform. If you do send the mount back to Celestron, ask for a shipping label if they don't voluntarily offer one. Some have posted that Celestron provided shipping labels, while others say they didn't. Seems to favor the ones that asked for it.

Just as an aside, my 152mm refractor was unknowingly twisted in its rings when I first mounted it on my CG5 and my Gotos were all off. After I changed to a more secure wider dovetail that kept the OTA straight, the problem was solved.

#4 zavisa

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Posted 30 January 2011 - 07:33 PM

I know you said you checked date, time, location, etc...but just as a fyi...I had a similar situation with my mount when I dst went to standard time and I forgot to change it.

#5 abrock5

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Posted 31 January 2011 - 10:40 PM

Thanks everyone! I think it has to do with the way I'm mounting my telescope. I'll put the foot mount back on and see if that solves it. Just curious though, I thought the calibration stars were supposed to compensate for cone error. Am I wrong in tins thinking?

#6 PHampson

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Posted 31 January 2011 - 11:17 PM

Rings can flex when the weight distribution changes, especially where they join the dovetail bar, and it doesn't take much to be significant. The mount does account for constant cone error but it can't handle cone error that changes when the scope slews which is what flexing rings would do. Make sure everything is really tight and rigid or go back to the mounting shoe..
Good luck.

Paul

#7 BlueGrass

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Posted 01 February 2011 - 01:13 AM

I mount my EON80 in a pair of WO 90mm split rings riding a WO V plate. I have the ADM CGEM dual saddle so the EON is at home on both my CG5 and the CGEM.






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