Telescope Reviews: Orion Skyview AZ Mount

This is a paragraph from the Desert Sky web page:
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DSV-1 'Steady View' Alt-Azimuth Mount
Designed for uncomplicated enjoyment of the night sky, the
DSV-1 provides simple grab and go, point and look operation
We craft the Steady View alt-azimuth mount from aluminum and stainless
steel components.

The shafts ride on ball and needle bearings to ensure
smooth movements and long lasting accuracy......
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Note what it says about using "Ball and Needle Bearings" . This design offers better accuracy and and smooth motion but also reduces friction to minimum.... making EXACT balance even more critical. That's the nature of the design. A balanced load WILL stay in balance regardless of elevation. But if you add wt or remove wt you will upset the balance and rebalancing is necessary.

Other types of alt az mount not using the side mount design may not require rebalancing but you are either relying on additional friction or a stress on the gear head to overcome the inbalance. Apply enough friction to an off balance fluid head and you no longer have a fluid head. A motor driven mount needs to be balanced when you attach a 3 lb binoviewer with two oversized EPs on the scope too.

The old Vixen Custom D Alt Az mount can handle a heavier load than the Orion Az-3 mount. It uses counter weight(s) for better balance:

http://cloudynights.com/item.php?item_id=797

Remember with a side mount alt az head you are relying on a threaded bolt about 1/2 inch dia to press down on a polished smooth steel shaft to increase tension. The EP location of my 6 inch F8 refractor could be as much as 3 ft from the mounting point. I need to apply a LOT of tension to hold a ~3 lb unbalanced load with a 3 ft moment arm when I remove the 50mm finder, Zoom EP and 2 inch diagonal altogether at the same time. I do not trust increased tension alone to hold the OTA.

Newton's law of motion: A body in motion wants to keep going.

I have several Bogen fluid heads. Including a 501 head rated for 13 lbs( no counter balance spring) and a 516 head rated for 22 lbs (16.5 lb fixed counter balance spring). Employing a counter balance spring works well..... up to a point. Unlike a side mount design the OTA sits ABOVE the axis of rotation, and the center of gravity shifts when you tilt up. The counter balance spring must be the correct match for the unbalanced load. Other wise you will be fighting spring tension.

I am using the Bogen 516 fluid head to mount my Miyauchi 100mm F7.5 binocular. OTA length is close to 30 inch and wt is ~ 15 lb with 7X50 finder attached. The 16.5 lb counter balance spring works great between ~+30 deg to +70 deg. Trying to view objects above +70 degs means I have to fight the spring force to keep the OTA pointed UP. Works fine at low power but at 54X with my hands on the dual pan handles I can see a bit a vibration in the EPs. I must rebalance by sliding the dovetail plate forward if I want to observe objects lower than ~ 30 deg also. Otherwise I will have to apply upward force to keep the OTA near horizontal. There is always a trade off.....

The newer Bogen/Manfrotto 501/503 HDV heads have different dial settings to vary spring tension to match the load. Should work better than the fixed spring of my 516 head.

Oh, I should add that Fluid Heads work fine with giant binoculars up to my Miyauchi 54X100. It's more difficult to make fine adjustments to track objects at higher power (100X) or more. I don't think I would use my fluid head at 150X even if it can support the load.

ERik D