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CGEM alignment VS: PEMpro

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#1 SanDiegoPaul

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Posted 16 February 2010 - 04:11 PM

Last night I decided to try PEMpro's Polar Alignment routine on the CGEM. First of course, I did the star alignment and followed with a Polar Align option, taking lots of care to adjust the mount with as much accuracy as the PA routine in the mount would require. I then did the UNsync step and followed by replacing one align star with Regulus and did a re-sync.

I had time on my hands and took the 9 steps to polar alignment in PemPro. It really took a LOT of work on the mount to get PEMpro satisfied. In other words, the PA routine built into the mount did not agree with PemPro at all

Any others with similar issue?

#2 j.w.white

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Posted 18 February 2010 - 12:57 PM

Hi Paul - I finally have some clear skies tonight so I'll do a quick PA comparison. From what I remember, the All-Star alignment didn't provide the most accurate polar alignment, and while I know I've used it as a basis for a PEMPro polar alignment, I don't remember how much extra work I had to do and I don't think I've ever done a drift alignment check afterward. I'll let you know what I come up with.

#3 SanDiegoPaul

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Posted 18 February 2010 - 02:47 PM

Thanks it would be great to have someone else compare too.

#4 j.w.white

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Posted 18 February 2010 - 02:59 PM

OK - after the initial PA with All-Star, I focused on refining that with PEMPro. I have to say, I found it a royal pain in the rear! So much so, that I gave up and moved on to a drift alignment. I don't discount for a second that this could be chalked up to user error (I had PEC on - should I have? Would a plate solve have given me better numbers than doing star imaging inside PP?). I'll have to post a few questions on the CCDWare site to try and get some resolution on this. Bottom line is that it really had me chasing PA - though it could also be due to relatively poor seeing. And to be fair, the PA that I did get from the All-Star/PEMPro combo was good enough to hold steady for 20 min. Not too bad......

On a separate note, I've made no secret about my issues with Az adjustments on the CGEM. I either had to loosen the mount much more than I would have liked (which cause movement of the PA when I re-tightened the mount), or had to apply some serious pressure on the Az adjustment knobs, resulting in me always overshooting the target. A user on the Yahoo CGEM group made the brilliant suggestion of using Slick Strips from Woodcraft.com and it has made a SIGNIFICANT difference! I can now have the mount as tightened down as I like and still find it easy to make Az adjustments. I highly recommend this (and really don't understand why Celestron hasn't added something of the sort).

#5 JadeSmith

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Posted 18 February 2010 - 04:18 PM

Where do you put the Slick Strips?

#6 shwright50

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Posted 18 February 2010 - 07:23 PM

I have to second John's comments about the efficacy of adding slick strips to the base (top of the tripod) of a CGEM. Without the tape, working the Az-bolts was a nightmare. I placed three, 3" strips on the outer, raised surface of the tripod top (this is the load-bearing surface on which the mount rests) and, as John noted, now the bolts adjust the azimuth very smoothly. Polar alignment can now be handled in a few minutes, zeroing in quite methodically on the alignment star. How good is the resulting alignment? I have yet to check my mount's PE (and I am interested), but I've been running 10 min guided sessions (using my new Monster MOAG), and my stars are round! I agree with John, Celestron is missing a bet not providing a "slick surface" to preempt end user hassles!

Steve W

#7 SanDiegoPaul

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Posted 19 February 2010 - 11:45 AM

Thatnks for the slick trick! On my Meade SCT, I use an old AOL CD rom (their only valid use) between the wedge and the pier or tripod to allow it to slip easily in RA

Can't do that with the config of the CGEM but I have wondered about how to get something in there. Your solution is a big help.

RE: PEMpro and PEC. I can't believe you had that much trouble refining your curve? That makes no sense to me. The program does it for you.

My PE was 13 peak to peak and PEMpro knocked over 10 arc seconds off that to a finished total of 2.5

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#8 j.w.white

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Posted 19 February 2010 - 03:00 PM

Naw - it wasn't the PEC, it was the Polar Alignment. The PEC goes off without a hitch. My PE last night (without PEC playback) was about 10 arcsec peak to peak. The PEMPro curve reduced that significantly. As you experienced though, it was the chasing of the polar alignment that caused me grief.






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