Enter Title

A "Yard Cannon" refractor mount: IMPROVED!

In the amateur astronomy community, long focal length (i.e. - long tube) refractor telescopes are semi-affectionately termed "yard cannons." They're long, they're bulky, and well - they kind of look like cannons in one's yard. So when I picked up a 5" diameter refractor lens in late 2008o, I had planned on making a "folded refractor" - or one that bounces the light off a number of mirrors, making for a small, compact telescope.

Then the guy who sold me the lens found the tube and focuser....

So I thought, "Hmmm... I can spend a lot of time trying to figure out how to accurately bounce light off three mirrors, and subsequently lose a lot of photons in the process, or just build a huge freaking tripod/mount and have a yard cannon."

Clearly, as evidenced by the picture below, I opted for the latter:


Photobucket

So how did I go about building this monstrosity? Well, first off, I knew I wanted to be able to have the eyepiece, when pointed at the zenith, be at a relatively "viewable" angle. That necessitated a rather high tripod. But when balancing the scope, I also realized that if it were to be that high at zenith, then the radius arm of the eyepiece would be HUGE, and therefore mean I'd need a stepstool (ladder?) to see anything below 40 degrees or so. Not the greatest option!!

I made use of the CAD software that I have, and figured that by using counterweights in the right places, I could have a scope that keeps the eyepiece in relatively "normal" heights, and also not be so heavy or difficult to move..

Photobucket

The tube is placed in a plywood "box" of sorts, that has the radius of the tube cut into the ends, with a removable top. The top then has four thumbscrews that allow for tightening the scope in place, or loosening it slightly for minor balance adjustments. It actually balances across a pretty wide range before requiring rebalancing (I'd estimate 35-45 degrees or so). The finderscope is bracketed onto that box, and is high enough that I can still stand and not have to contort too much to point towards the zenith.

Some rather convenient PVC plumbing parts are used as the bearing surfaces, which then rest on nylon furniture glides. It has very smooth movement in the altitude axis using these items, even supporting the 25 or so pounds of the scope, box, and counterweights. The handle is placed so that when transporting the scope, it balances and remains level.

finderscope, scope box and bearings

Some upgrades that I did to make it better than the old mount: 

  • Replaced 6" Lazy Susan bearing on azimuth axis with a 12" Lazy Susan bearing
  • Added bolts through the azimuth top surface to allow for removable altitude "U"-shaped cradle
  • "U"-shaped cradle is secured using knobs, also allowing for quick removal, instead of being screwed in place
  • Tripod legs were shorted to account for cradle adding height over azimuth axis

I've used this mount a couple times now, and it is VERY smooth, VERY easy to point, and is also much easier to move in and out of my house. It's quite handy to have the large azimuth surface on which to place eyepieces and binoculars. And I've actually had several ideas of how to be able to use the "base" (minus the "U"-shaped cradle) as a platform for both a binocular mount and perhaps a fork-mount for my Orion ST-80 refractor.

This has turned out to be quite a nice mount, and didn't cost me an arm and a leg, either! I probably have less than $100 in it, even with the redesign.


UPDATE: October 15, 2012

I did sell this telescope.  However, the mount worked very well as an alt-az mount, and was definitely a vast improvement over the initial design.  If you have a larger refractor and can't afford a large equatorial mount or don't have a place for a permanent pier, this is definitely a useful option to consider building.