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EdgeHD/CGEM tracking
So I had a chance to try my 1100HD with the Starlight Xpress H9C. My biggest concern is that I can't seem to take a shot longer than 5 seconds, then the tracking starts to slip bad enough where the stars are oblong and blurred. I am still working on focusing, but I do know the tracking slips. For example, if I will center the M51 galaxy in Nebulosity, and after I take about 20 ten second shots, it will be just outside of the Nebulosity Frame and Focus crosshairs by the end of the shot series. This is seriously messing up my images. I have made sure to correctly balance the scope. Alignment is good, because after it drifts, I will tell it to go to M51 again, and it'll be dead centered. My only thoughts are that I need an autoguider for any shots over 10 seconds and/or the scope is too heavy for the mount and it's slipping. All I have on the mount is the scope, camera, hyperstar, feathertouch/microtouch drive focuser, dewshield, & telrad.
I usually do a 2 star alignment with Arcturus and Dubhe, then Calibrate with Vega and Antares. I need to learn how to do a Polar alignment to make this better. I bought an SXV autoguider, but its backordered so I will just have to wait and see if this fixes the problem.
I usually do a 2 star alignment with Arcturus and Dubhe, then Calibrate with Vega and Antares. I need to learn how to do a Polar alignment to make this better. I bought an SXV autoguider, but its backordered so I will just have to wait and see if this fixes the problem.
Replies to This Discussion
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Permalink Reply by Lisa Kaminski on
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I will try to ALLSTAR align process next time I get a chance. I have a hyperstar conversion, which reduces my focal ratio down, probably similar to the focal reducer...although I'm not sure if that's what they call it.
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Permalink Reply by Charles Dunlop on
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I'd definitely use hypertar with this setup, F11 will be very difficult to get good pinpoint round stars.
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I think hyperstar is at F2.
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Is that too much weight for that mount?
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I have heard that you don't want to add to much weight to this mount, but the telrad and camera pretty much weigh less than a pound combined. The dew shield probably weights half a pound and the hyperstar might weigh a pound. That's it.
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Proper alignment will help significantly for sure.. but I'm pretty sure that the mount isn't truly capable of that level of weight at that focal ratio with long tracking. I've got the same basic setup only on the CGE pro and I'm worried about getting shots at F11. Celestron always overstates the quality of their mounts in the marketing... shocking I know. lol.
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So based on what Celestron says the CGEM is capable of a 40 lb payload. The 11" SCT is 28 lbs. and my equipment added can't be more than 3-4 lbs extra. I just can't see that being the reason why the tracking is slipping.
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it's a heavy load for that mount, no matter what celestron says, but you shouldn't be slipping totally off like you are. Allstar alignment, you aren't polar aligned or else you aren't well balanced. Did you try rebalancing? Instruction manual tells you how to appropriately balance.
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I figured it out. It was the polar alignment. Basically...I wasn't doing it. :)
It made all the difference.
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Permalink Reply by Greg Marshall on
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I'm glad it's working now. If you stick with using the hyperstar setup it will probably work well. However, there are some issues with guiding the CGEM that might still be waiting to trip you up. Watch for failures in guiding the DEC axis.
I would agree with the comments that 28 pounds is a lot for this mount (for astro-photography, that is), but there are many factors affecting how well a mount will perform. I used a CGEM until very recently and my whole imaging system weighed about 28 pounds - maybe more. I got it to work, but it was not easy.
At f/2 an 11 inch scope has a focal length of 559mm, which is quite reasonable for the CGEM. At prime focus it is 2800mm, which is way beyond reasonable for long exposures on this mount. Even with excellent guiding, the residual errors in the RA drive train would result in very blurred images.
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Please stop replying to my posts. You are rude and unhelpful. You can reply when you calm down and stop rudely telling people how they are doing things wrong. Who in the hell are you anyway. I dont think your character fits this forum.
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Permalink Reply by Marc Basti on
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Hi Lisa, here's another resource for the Celes. PA routine it's a bit clearer than the Celes. manual (I think).
http://f1.grp.yahoofs.com/v1/EGs2TnKU2NglFyN-qVLAxGLkcFFmHRyVGiuWgT...
If for some reason this link is messed it's on the yahoo cgem users group- files-enhanced PA routine. This other site is good to check out, good bits of info.
http://www.nexstarsite.com/
We're all willing to help (cos we all needed it at one time). Marc
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