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Richard Turner
super member
Reged: 01/25/09
Loc: NC
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CGEM periodic error
#3184054 - 06/26/09 01:31 PM
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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
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Steve Self
member
Reged: 11/27/03
Loc: Daphne, AL
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Re: CGEM periodic error
[Re: Richard Turner]
#3187973 - 06/28/09 11:40 PM
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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
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chollman
sage
Reged: 04/24/08
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Re: CGEM periodic error
[Re: Steve Self]
#3188196 - 06/29/09 02:50 AM
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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
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donsinger1
sage
Reged: 10/28/07
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Re: CGEM periodic error
[Re: chollman]
#3190333 - 06/30/09 03:12 AM
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Quote:
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
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Ian Robinson
Carpal Tunnel
Reged: 01/29/09
Loc: Gateshead.NSW ,Australia (33S ...
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Re: CGEM periodic error
[Re: donsinger1]
#3190366 - 06/30/09 04:22 AM
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50-60" PE is terrible.
Without (auto)guiding you'd be hard pressed to get round stars even in widefields with short lenses.
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Richard Turner
super member
Reged: 01/25/09
Loc: NC
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Re: CGEM periodic error
[Re: Ian Robinson]
#3190381 - 06/30/09 05:22 AM
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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
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Ed J
member
Reged: 05/31/07
Loc: Tujunga, California
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Re: CGEM periodic error
[Re: Richard Turner]
#3190921 - 06/30/09 01:12 PM
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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.com/photos/edhiker/3662276245/
Ed
Edited by Ed J (06/30/09 01:13 PM)
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