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First-time user of alt-azimuth mount

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#1 hottr6

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Posted 03 February 2013 - 02:02 PM

In all my time in astronomy, I have preferred GEMs, and have viewed alt-azimuths with profound suspicion. Time I thought to dip my toes in the world of alt-azimuths.

I picked up a single-arm mount for an Orion Starblast 6, and attached my portly Meade 6" f/5 Newt. I say portly because the tube is thick steel, and I have added a 2" Crayford and Vixen 6x30 finder stalk and shoe. This is one heavy mother, resembling more a Russian T-34 tank.
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I decided to spend the night with my Meade 32mm SWA smoothie, 24mm S5K SWA, 18mm S5K UWA, 14mm UWA smoothie and 8.8mm UWA smoothie. Targets were M33, M45, M42, Double Cluster, and sweeping the remains of the summer Milky Way. Best views of the night was the 18mm and 8.8mm UWAs. Worst view was the 32mm SWA.

When loaded with the heavy eyepieces and the OTA balanced, I did have a clearance problem with the mount base, and so could not get anywhere close to the zenith.
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Up to this point, I was delightfully surprised with the alt-az. With the low magnifications(the 8.8mm yielded only 85x) and wide fields being used, I had no problems with tracking objects. The rig was considerably underdamped, and would vibrate for several seconds after adjustments, but the wide fields made adjustments infrequent. I did not try it at higher magnifications, and suspect that I would have been less pleased had I done so.

Carrying the combined rig was super easy! What a joy after wresting GEMs! But what to do about viewing near the zenith?

Solution: A 5" f/5.
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So here is my heavily modified 5" Newt, again with 2" Crayford, heavy eyepieces and heavy finder. When the OTA is balanced, no clearance issues!
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The only downside to this setup is that the 5" is no 6", and the views suffer. I have been thinking a long time about putting the Meade on a weight-loss diet. I am now more motivated than ever.

#2 coopman

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Posted 03 February 2013 - 05:45 PM

I don't know how feasible this is, but you could add ankle weights (or some other kind of weight) to the back end of the OTA so that the balance point shifts towards the back.

#3 iluxo

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Posted 03 February 2013 - 11:37 PM

Since you said it has a steel OTA... place some big heavy magnets inside the rear end of the OTA, enough that it doesn't scrape the bottom of the tube on the mount.

#4 hottr6

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Posted 04 February 2013 - 08:33 AM

Good tips, all doable and good interim solutions. I'm still going to rehouse the Meade optics, because the OTA is too much for my Vixen Polaris GEM.

Darn, if it isn't one thing, it's another. Ya find something that seems to be the bee's knees, but it falls short in just one vital area.

#5 Cliff Hipsher

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Posted 04 February 2013 - 09:53 AM

I don't want to sound like an *BLEEP*, but why bother? Its obvious to me the mount was never intended to carry that Meade OTA.

This reminds me of a saying we mechanics have regarding modifying cars and motorcycles: Performance, Reliability, Cost. Pick any two...

But, its your money...

#6 hottr6

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Posted 04 February 2013 - 10:51 AM

This reminds me of a saying we mechanics have regarding modifying cars and motorcycles: Performance, Reliability, Cost. Pick any two...

Having built and raced cars and motorcycles most of my life, I'm used to picking one....






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