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Setting Circles Not Accurate


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Hi!

Some of you might remember me as the noob from the q's on focusing, and unfortunately I have another beginner question, this time on setting circles.

So I recently bought my first telescope, a Celestron 130 EQ, and after doing a fair bit of observing visible stars and planets, I tried to hunt for some DSO's using the celestial co-ordinates from the app on my phone. However, when I aligned the setting circles to the correct points, nothing could be seen. Ultimately, I did find the object using my naked eye, and it was way off from the co-ordinates given.

After repeating this with a few other objects, the issue remained. I have my latitude put in on the altitude dial, mount is aligned with Polaris, but the issue remains. I heard that sometimes the setting circles pointer can be wrong and needs to be adjusted, and if so, how should I do it? Is there any other reason for this to be happening? 

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Setting circles on small mount are notoriously difficult to use as their resolution is so low but:-

To align the RA setting circle:

1 .Locate a bright star near the celestial equator The farther you are from the celestial pole the better your reading on the RA setting circle will be

2 . Use your star atlas or you astronomy app to lookup the coordinates of the star you selected

3 . Center the star in the telescope’s eyepiece

4 . Without moving the telescope, rotate the RA setting circle until the RA indicator points at the RA coordinate of the star you selected *

NOTE: The RA setting circle does NOT move as the telescope moves in RA, the setting circle must be aligned each time you want to use it to find an object. However, you do not need to use a star each time. Instead, you can use the coordinates of the object you are currently observing.

Have you definitely got stage 4 correct?:

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The small setting circles on modern mounts are just for show. The accuracy of setting attainable often represents an error angle wider than the field of view in the eyepiece. In the days before GoTo, setting circles were much bigger. I have seen some in Victorian observatories that were about 2 feet across.  I tried using the setting circles on my EQ-5 to aim a 203mm Newtonian but it was rather a waste of time.

To make setting circles work, you probably have to polar align the mount with the precision needed for astro-imaging, rather than the 'point it near Polaris' that suffices for visual observing.

Edited by Cosmic Geoff
EQ-5
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1 hour ago, Torutro said:

I'll give it a go tonight, but just a quick question, will the dec circle also be accurate then, and is it just an issue with the ra circle?

Unfortunately, 'accuracy' is a relative term here because of the resolution that I mentioned which applied equally to the Dec axis! Personally, I would really recommend star-hopping when using this mount as you are more likely to achieve success quickly.

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I could never get the ones on my Tal-1 to work but probably gave up too quickly. I think iirc that one of them was reversed which made things more complicated. The Hour Angle ones on my Telementor mount oth are fab- no need to keep referencing other stars after initial setup and pretty accurate. Sorry that doesn’t help you though. 

Mark

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4 hours ago, Torutro said:

So I recently bought my first telescope, a Celestron 130 EQ, and after doing a fair bit of observing visible stars and planets, I tried to hunt for some DSO's using the celestial co-ordinates from the app on my phone.

Hi, I have the same scope. The setting circles are not the easiest to work with. I would suggest using an app such as Skeye to help guide you (it has PUSH-TO functionality), or use the good old way of star hopping. Use a low magnification eyepiece to start with to locate the object and then you can use higher magnifications (if you wish).

First and foremost, have you aligned your finder to the scope? That was my first challenge, hence asking :)

Good luck.

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