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Trailing stars problems


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Can anyone shed some light on what might be causing the trailing stars even at short exposures of 20 seconds?

Here's 2 images from the beehive cluster, 1 showing trails at 30 secs and another which looks ok at 3 mins. Seems to be intermittent.

 

Grateful for some help

Thanks

st1.thumb.jpg.b38436274a8b5af86a89d697e33d8058.jpg

st2.thumb.jpg.a1e42e101ea7aaf5011b54765e184d96.jpg.e26e7f109baac1df934fdfc8c2f8cb5b.jpg

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The short exposures were not guided, i was taking short test shots to make sure I had the target in view.

There was more than 1 image that had trailing and I was stood away from the scope. I also had it with some of the 3 minute exposures. Could they all be because of cables hanging down?

Does the fact I had a mix of good and bad point to a tracking issue or make it less likely?

 

Thanks

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Knocked, wind, periodic error (quite harsh one), balance issues and backlash? The cables could be a cause too. Best to attach them as much as you can to the telescope, with them still being able to move as the telescope slews/tracks.

When I got my Celestron AVX mount, I often saw star trails, more often with longer exposures, logically, but not always. And I found out that it was because of periodic errors in the wormgear.
The AVX has Periodic Error Correction learning, and after I did that, and applied it, I went from having to scrap every 2-3 frames, to being able to do 4-5 minute exposures without guiding, as long as polar alignment was very good.

Might not for certain be the issue here though.

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Looks indeed like a balance issue or a gear skip problem in the mount: if the weight is not well balanced (or TOO well balanced) the mount might skip one gear tooth from time to time, which gives you the tiny line to the side you see. Depending on how big/small the issue is it could only pop up every couple of minutes or so.

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OK, I'm not an expert by any means. On the first image the "trail" is exactly in line with the spider star lines. On the second image , the spider lines are there (but rotated from the original) and no "tailing". Could it be a reflection off the spider in the first image and you have re-positioned the Scope on the second image hence no reflection?

The 2 images are inverted from each other. Did you have a meridian flip?

Geoff

Edited by Spitfire
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