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CG5 Polar axis scope

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#1 tim57064

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Posted 11 October 2012 - 08:47 AM

Having a lot of fun trying to get polar axis scope for my cg5 aligned.First of last weekend a couple of friends and I wer attempting to align a friends scope,also a cg5. Turned out his polar axis scope somehow got bent and was having a lot of fun trying to align.So I then gave him my new polar axis scope from my setup,also a CG5. Well we thought we were following the instructons on how to align when the screws went thru and into the axis scope itself. What the heck! When we were rotating the axis on the mount we were not getting perfect circles they were oblong. We were using a web cam I had converted to use for photography yet we found we could see the etched reticles and the reference spot we were using to align the polar axis scope. We were never able to align properly. I now purchased a new polar axis scope for myself and would appreciate any help anyone can offer on the subject. The instructions do not cover a lot. I apologize if this is too lengthy a topic.Has anyone else run into this trouble with the scope? Tim

#2 mclewis1

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Posted 11 October 2012 - 01:21 PM

Tim,

Yes it's a bit of an issue. There are however some good tutorials online and in some other threads here on CN.

The bigger question however is why bother with the scope? For visual work you can usually just "eyeball" the polar alignment close enough. With the All Star polar alignment routine in the hand controller you can get just about as good a polar alignment as with the scope, and if you are imaging you'll probably be wanting to do an accurate drift alignment anyways.

#3 tim57064

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Posted 17 October 2012 - 09:07 AM

Tim,

Yes it's a bit of an issue. There are however some good tutorials online and in some other threads here on CN.

The bigger question however is why bother with the scope? For visual work you can usually just "eyeball" the polar alignment close enough. With the All Star polar alignment routine in the hand controller you can get just about as good a polar alignment as with the scope, and if you are imaging you'll probably be wanting to do an accurate drift alignment anyways.

First off thanks for the reply. You say why bother with the scope? Well, I do realize that when imaging, you need to be properly aligned in order to properly track and keep the object you are viewing and imaging in the center of the field of view. As far as accurate drift, I really am not sure what you are referring to. I have seen that somewhere just don't remember where.I have Canon BackYardeos I believe I saw it there.How does it work? Not totally up on all the aspects of imaging yet.Obviously. Thanks, Tim

#4 mclewis1

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Posted 17 October 2012 - 10:18 AM

Tim,

With computerized goto mounts there is an important distinction between pointing or goto accuracy and tracking accuracy. The first is totally dependent on how well you do your initial alignment (how accurate the sky model is and how well your particular mount points to objects with that model). You can get a very accurate initial alignment without having a very accurate polar alignment. This is where the by eyeball comment comes in. For folks who are not imaging they can skip any polar alignment routine by simply pointing the mount roughly where Polaris is (or the southern celestial pole). The initial alignment is then done and the mount will now goto objects all over the sky. For most folks this is all they need.

The tracking of an object will however be dependent on the accuracy of the polar alignment. Again for visual work a little drift in the tracking of an object over time isn't usually a problem. But for imaging it obviously is an issue.

Originally Celestron provided a basic Polaris oriented polar alignment routine in the hand controller. This got you close to a reasonable polar alignment. For more accuracy there was the polar alignment scope. This could be used in place of the hand controller routine or to augment it. For serious imaging there is also drift alignment procedures which can improve the polar alignment beyond that of either the hand controller routine or the polar alignment scope. Serious imagers always seemed to rely on the drift alignment (there are a number of tutorials on how to do this posted here and on various websites). Some folks also swear by the polar alignment scope and indeed if someone takes the time to set one up and use it properly it can provide very accurate results.

With hand controller firmware v4.15 Celestron introduced something called All Star polar alignment. This routine replaced the original polar star oriented routine (but it actually isn't labeled "all star" anywhere but the manual). This is a very accurate polar alignment capability that for most folks replaces the need for a physical polar alignment scope. Yes if you are planning to image with a CG-5 at focal lengths beyond 500mm or so and to take lots of exposures over a minute or so then it's still a very good idea to also do a drift alignment to tighten things up and remove as much polar alignment error as possible. There are however still a number of folks who developed the capability to do a good polar alignment with the scope and don't bother with the all star routine.

There isn't any particular right or wrong in all of this, it's mostly what you are used to or what simple works for your needs. For most folks though the all star polar alignment simply replaces the need for the polar alignment scope.

#5 DaveJ

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Posted 17 October 2012 - 10:20 AM

First off thanks for the reply. You say why bother with the scope? Well, I do realize that when imaging, you need to be properly aligned in order to properly track and keep the object you are viewing and imaging in the center of the field of view. As far as accurate drift, I really am not sure what you are referring to. I have seen that somewhere just don't remember where.I have Canon BackYardeos I believe I saw it there.How does it work? Not totally up on all the aspects of imaging yet.Obviously. Thanks, Tim


I'll add that the accuracy of polar alignment using ASPA (All Star Polar Alignment) is better that that using a polar scope. As stated, for astrophotography, a drift alignment is still required. I found this site quite helpful and it allows you to virtually practice during the daytime, too.






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