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CGEM periodic error

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#1 Richard Turner

Richard Turner

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Posted 26 June 2009 - 12:31 PM

I just bought a CGEM a few days ago. I was interested in how much periodic error was in the RA worm. After a drift alignment, I seemed to get an estimated periodic error of around 50-60 arcseconds.

When compared to a less expensive mount, say, an LXD-75,
it seems that the extra money for the CGEM buys more
load capacity, not less periodic error. My LXD-75 seems to
have a comparable amount of periodic error.

I tried PEC, and it did help to get rid of some of the worm error amplitude.

The mount was purchased for imaging as well as visual use.
I was wondering what experiences others might have had with a CGEM mount.

Richard

#2 Steve Self

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Posted 28 June 2009 - 10:40 PM

Richard,

I am interested in what others have to say about this also. I have a CG-5 mount and I am considering a CGEM for the extra load capacity.

Hopefully some CGEM owners will chime in.

Steve

#3 chollman

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Posted 29 June 2009 - 01:50 AM

I use an Orion auto-guider and I am getting 6 min. plus exposures with round stars in an 8" F/8 Newtonian with my CGEM. Charlie

#4 donsinger1

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Posted 30 June 2009 - 02:12 AM

I use an Orion auto-guider and I am getting 6 min. plus exposures with round stars in an 8" F/8 Newtonian with my CGEM. Charlie


Same here....my max exposure time autoguiding with PHD and an Orion SSAG is 5 minutes with an F7 105mm refractor, and that is primarily due to limiting light pollution. Round stars and little drift. The Polar alignment routine works well, and it is dumb simple. With good autoguiding, pec becomes much less of in issue in imaging.

Don

#5 Ian Robinson

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Posted 30 June 2009 - 03:22 AM

50-60" PE is terrible.

Without (auto)guiding you'd be hard pressed to get round stars even in widefields with short lenses.

#6 Richard Turner

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Posted 30 June 2009 - 04:22 AM

Last night I was able to use PHD with the CGEM mount, and got round stars, nicely guided, with 4-minute exposures.

Yes. Autoguiding is a must for exposures that are more than a few seconds long.

Richard

#7 Ed J

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Posted 30 June 2009 - 12:12 PM

I've had better results. On a crosshair, I estimate p-p error to be about 20" on Saturn(first light tests).
A stack of 30 sec exposures of M51 is at: http://www.flickr.co...ker/3662276245/

Ed






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