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equatorial mounts and accuracy of setting circles

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#1 mellowgeorge

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Posted 16 October 2012 - 08:46 PM

My GOTO Alt-Az mount has had electronic issues.

I am now considering going to a German equatorial mount for my 90mm f/11 refractor.

I was eyeing Celestron's CG4 mount mostly for visual observing, maybe some CCD webcam imaging of binary stars and the moon, planets.

I have no view of polaris from my backyard, which is where 90% of my observing will be done. I like the GOTO aspect of my Alt-Az for finding Messier objects.

Will the setting circles bring me close enough to these fuzzies?

How critical is perfect polar alignment?

I have no direct view of polaris from my backyard, where most of my observing will be done.

I appreciate any input. Thanks!

#2 Jim Curry

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Posted 16 October 2012 - 09:56 PM

A 90 f/11 will probably be pushing that mount. I have a 4" f/12 on a CG5 and it's at it's limit for settling down after focusing. If it's a very light tube you might get away with it but it's the length that's a killer.

Jim

#3 Jon Isaacs

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Posted 17 October 2012 - 12:52 AM

A 90 f/11 will probably be pushing that mount. I have a 4" f/12 on a CG5 and it's at it's limit for settling down after focusing. If it's a very light tube you might get away with it but it's the length that's a killer.

Jim


Which CG-5 do you have? The CG-5 with the 2 inch SS legs ought to handle a 4 inch F/12 refractor reasonably well, the do put C-11s on them. The modern CG-4 with the 1.75 inch SS legs handles a 120mm F/8.3 reasonably well, it ought to handle a 90mm with the same focal length...

As far as using the setting circles to find targets, they are not that accurate but they can get you close.

Jon

#4 Jim Curry

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Posted 17 October 2012 - 05:19 AM

I have the 2" SS legs. Like I said, it works but it's pushing it.

Jim

#5 rmollise

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Posted 17 October 2012 - 06:38 AM

The small circles of this mount will get you in the general vicinity of the target if you are decently polar aligned, but that is it.

#6 mellowgeorge

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Posted 17 October 2012 - 12:15 PM

OK, thanks for the input re: the Celestron CG4.

Is the Orion Skyview Pro eq. mount that much better than the CG4? The price difference is substantial though the specs are somewhat close.

There must be a quality difference between the two. Is that true?

Getting an object within 1-2 FOVs of a low-power eyepiece is perfectly fine. Is that a reasonable expectation with the mount's setting circles?

#7 rmollise

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Posted 17 October 2012 - 12:37 PM

All these GEMs have setting circles that are just too small to be of much use. I can routinely get a field or two away from a target with analog setting circles, but i am talking about the substantially larger circles on a fork mount SCT. Which does NOT mean the circles on these mounts are of no use. In concert with a good 50mm finder they make locating quicker than with "just the finder." For the best accuracy, the better the polar alignment, the better. Don't think you can just eyeball Polaris and get very close to your targets.






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