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Orion AZ-3 Alt-Az Mount

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#1 xcy

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Posted 10 May 2011 - 03:15 PM

Would the Orion AZ-3 Alt-Az Mount be sufficient for a 4" f/9 ED refractor with a 9x50 finder, a 2" diagonal and a 2" eyepiece (for example Agena 38mm 2" SWA)?

#2 tommy54

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Posted 10 May 2011 - 04:25 PM

I would say probably not. I had one years ago and tried to mount a Takahashi FC-76 to it,"about 6 pounds". It would handle it in Azimuth, but not in Altitude. It was straining.
Best Regards...Tom.

#3 george tatsis

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Posted 10 May 2011 - 10:03 PM

My friend John used to have the exact set up you mentioned. The answer is that there was some minor 2-3 second vibration which was improved when the 9X50 finder was substituted by a red dot unit and the 2" diagonal by a 1.25" one.These two, the 2"dia. and the 9X50 finder weigh about 1kg(2.2lb).The average red dot and 1.25" diagonal weigh 370gr. That's a big difference.

The overall performance was excellent, considering how inexpensive the mount is.

Moreover, the performance of the scope can be improved if you balance the tube at a 60* angle and not horizontally.By doing so , the vibration is reduced even further.

In addition, an even better solution would be to come up with a reversed L shaped bracket and mount the scope parallel to the central axis of the altitude gear and NOT atop,which is the current set up.

I'll try to get some pictures I had seen years ago and get back to you.

George

#4 george tatsis

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Posted 10 May 2011 - 10:15 PM

I haven't been able to come up with the pictures yet, but I found something equally interesting.

http://www.spacegaze...sp?pageid=97490

There is no weight difference between the TV85 and the 100ED. I know because I have both!

George

#5 george tatsis

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Posted 10 May 2011 - 10:26 PM

Another solution based on the principle I mentioned above.

http://www.homebuilt...odification.htm

George

#6 xcy

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Posted 11 May 2011 - 09:59 AM

Why is it a better solution to mount the scope parallel to the altitude axis and not atop?

#7 Eddgie

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Posted 11 May 2011 - 01:00 PM

I would SOOO not put a 100ED on an AZ-3 type mount EXCEPT or terrestial use.

These mounts are very poorly suited to Astronomical use.

The problem is that the altitude axis really isn't designed to be used with a telescope pointed higher than about 30 or 40 degrees in elevation.

The problem manifests itself in the tendency of the scope to "Cascade" back when you point it to higher elevations.

As you tilt the scope back, the center of gravity moves behind the head. This puts more pressure on the altitude friction washer, and the axis will start to creep.

You can tighten up the nut that changes the pressure on the axis, but when you do this, it makes the mount very stiff.

Generally by the time you get the nut tightend enough to hold the scope at all orientations, it becomes too stiff to move easily.

I OWN one of these, but I use it 100% for birding and terrestial (C5 mounted on it).

I tried using it for astronomical purposes before though, and did not like it at all.

I think you would be far better served by going to one of the new mounts that are specifically designed for astronomical use. These ususally have standard dovetail saddles (which is good for balancing) and pivot though the center of the OTAs longitudinal axis. No problems with creep when the scope is balanced.

So, just my opinion, but I think you can do FAR better than an AZ-3 for astro use.






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