ALT/AZ MOUNT

The ST-80 is a great deal for a low-cost, wide-field telescope (see my page on modifying the ST-80, and it's siblings, to maximize its performance).  It is best used for casual, slow scanning of large areas of the sky.  As such, it really needs a smoothly operating alt-az type mount.

I originally tried using a photo tripod with a fluid head, and while it pretty much worked, you had to continually adjust the tensions to keep the scope from flopping down when you let go.  If you got it tight enough to stay put, then it couldn't be easily moved.  Even if you found the magic angle and tension to allow it to easily be moved and yet stay put when you let go, when you let go of the handle the flex that was introduced into the head and tripod during movement would unload and swing the scope a few degrees off target.  Mucho frustration.

I looked at a few different mounts at star parties and didn't like any that I saw.  They were universally heavy and complicated.  I also looked at the Televue alt-az mounts but couldn't justify spending a whole lot more for the mount than the scope I was putting on it, though they are very nice mounts.  Then one day I opened Sky and Telescope and saw a mount that was pretty much what I was looking for.  <(Don't remember the issue,  look somewhere around winter 2001).  I made some changes and came up with this mount.  I was having some difficulty getting the scope to balance and behave (if you could see the bottom of the altitude box the scope mounts to you would see a row of holes where I tried moving the scope back and forth).  Guess what?  The next Orion catalog had their new Dobs in it with their spring tension system.  Viola.  Success.  They set theirs up as a counter balance, mine is pure tension but it still works.

Building the mount is pretty straight forward.  Mine is built with 1/2" Appleply and 3/4" cabinet grade AA for the base and arms.  I used glue-on Teflon chair glides on both the altitude bearing and the ground board.  The ground board also has a piece of vinyl floor tile glued to one side for the Teflon to ride against (suggestion - look for a sink cutout, with Formica, at the local cabinet shop). The altitude bearings are cut from solid oak and banded with Melamine edging. 

Tune the mount using Rain-X and alcohol.  Rain-X makes the vinyl and Teflon super slick, the alcohol removes the Rain-X from one or more surfaces to provide a little sticktion (old Dob trick).

This mount WILL NOT handle the weight of a camera on the scope, but does provide a SUPER experience at easily scanning the skies.

   

   

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