Easy Alt/Az Mount Modification

Rod Nabholz

 

It seems that anybody who has been around the hobby of Astronomy for any time at all finds themselves on a quest for a low hassle, quick to set up scope that will serve well when we have just a little time, little space or a little gumption. The well worn term “grab and go” was coined to describe this elusive set up.

 

For many, including myself, a short tube refractor fills the bill. But identifying the scope type leaves us short a critical component. We need a simple mount.

 

My Tele Vue Pronto was the scope, and I had perched it atop a sturdy tripod with a fluid head. It was less than perfect. Balance was always a problem – It was more frustration than fun. Not likely to make me want to “grab and go” too often. I began to look around for a better mount.

 

There are a great number of vendors that offer very specialized Altitude/Azimuth (AltAz) mounts to fill this niche. I was actively shopping for just such a mount when in April 2005, Sky and Telescope Magazine ran an article by Alan Adler titled "A Simple Altazimuth Tripod Adapter”. It seemed to be just what I was looking for.

 

Adler put his finger right on the issue I was having with my set up – The center of gravity of the scope was way above the rotation axis of the head – It could never provide a smooth balanced movement.

 

His solution, brilliant in its simplicity, was to use an adapter to bring the scope down to where the center of gravity was even with the altitude axis of rotation of the tripod head. The photos in the article and the text described a simple 1x4” board that did the trick for his scope. This looked like it held some promise.

 

The construction was so simple and cheap, that I felt I had nothing to lose by giving it a shot. I used a scrap of black ash left over from a previous project. I ripped a piece that was as wide as the platform of my tripod head. For length I simply eyeballed how far it would need to extend to the side to make room for the scope to clear the head and tripod.

 

For hardware, just a couple of things were needed. To attach it to the tripod, a ¼” 20 T-Nut. To attach the scope to the adapter, a ¼ 20 bolt to mate with the tripod screw hole on the mounting collar of the Pronto. In my case, I had a nice knob with that threading left over from another project that I used. Total hardware cost about $3

 

For my Pronto I simply drilled the two holes – one for the T-Nut and one for the scope attachment on the centerline of the board. Depending on the T-Nut you have, you may find that you need to countersink it a bit to place the threads within reach of the tripod head's mounting bolt.

 

Your scope's mounting method may mean that you have to drill holes in a different configuration, but you can certainly make the necessary changes easily enough.

 

For my set up the one board was all that was needed to place the scope's center of gravity on the rotation axis of the head. You may find that you have to adjust slightly to make things come together for your set up. You can add a thin spacer board on either end as necessary to bring things to where you need them.

 

I took the extra steps of rounding the corners, sanding and finishing it with a couple of coats of polyurethane to help it stand up to the elements a little better. You could get away without doing the same if you wanted to. Heck, when it is this cheap to make, you can make a lifetime supply of spares for $10.

 

To use the mount, simply attach it to your tripod head, make sure to tighten it securely. Failure to do so could cause the adapter to rotate when you have the scope inclined in altitude bringing the tail end into the tripod.

 

Mount your scope to the underside of the adapter taking care that you balance the scope front to back. Be sure and add your diagonal and eyepiece before balancing.

 

When positioned and balanced correctly, the scope should remain stable when you slacken the tension on the altitude lock on the head. Admittedly, a fluid head makes this critical balance a little less important and I would recommend that you choose a fluid head if you need to buy one.

 

A tripod with a center column allows you to raise the scope up to avoid contact with the legs when the scope is near the zenith. Remember that raising the center column will diminish the stability some, so be conservative or adjust your expectations accordingly.

 

Many fluid heads offer a handle to tilt the head – it is a welcome convenience as well

 

In use it is a real pleasure. The scope goes where I want, and stays where I put it – All you can ask of a mount. The cherry on top is that it was easy and cheap, - All you can ever ask of an Astronomy Project.

 

Thanks Mr. Adler – well done.

UPDATE

The bottom side mounting of the finder as pictured above was less convenient than I would have liked. A much better solution for mounting a finder to this kind of set up is by attaching a red dot finder with another Home Built Astronomy Project - A Cheap and Simple Red Dot Finder Mount, as seen here.

 

I welcome your comments and questions at

rnabholz@yahoo.com

 ©2006 Rod Nabholz

 

Twin Tube Telescope * Manual Dob Setting Circles * Binocular Chair

Kid Peek Telescope* Downward Looking Binocular Mount * Easy Alt/Az Mount Mod

Barn Door Mount * Observing Stool * Cheap and Simple Red Dot Finder Mount

PST Eyepiece Shield Eyepiece Case Key Reel Red Light Keeper

Kid Peek II * Observation Log and Sketching Forms * Telrad Dew Shield

 

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