Solving balance issue in alt/az mount - a REALLY simple jig

[mental4astro (Alexander)]

Hi all,

My recent experience with big binoculars on a photo tripod has brought to light a problem of mounting an instrument onto a mount that sees the instrument sit high on top of the tripod head. With the binos or scope sitting so high, it becomes very difficult to achieve a smooth and stable altitude action. The instrument tends to fall backwards and there is a need to really tighten the altitude clamp to secure the instrument.

My big binoculars were really difficult to control when I had them mounted onto my photo tripod using the tripod adapter. The altitude clamp had to be over tightened to hold its position, and the altitude motion was difficult to control and a risky propositon should you forget for a moment that the thing wanted to fall backwards when you loosened the clamp.

The solution is to seek to bring the centre of gravity (COG) of the instument in line with the pivot point of the tripod head.

This is not my discovery, but one I found with my looking into a new alt/az mount and/or solution to the problem I had. In my search I came across a really nifty and oh so simple tripod platform to bring the COG of the instrument in line with the pivot point of the tripod head. Home Built Astronomy Projects offered this alt/az platform solution that I'm now raving about, .

I've just bought an 80mm f/5 refractor with a 2" focuser for my astro fetish of wide field viewing () from fellow IISer stringscope - many thanks Ian!!! I've coupled to it Mr Eyepiece, a 34mm Meade SWA eyepiece, weighing in at a beefy 785g. Mounting this combination on top of my photo tripod would not make for a stable situation. I mentioned to Ian the above tripod solution, and he suggested a mounting jig to fit the 80mm refractor. Below are a few pics to the new rig coupled to my photo tripod.

The solution is wonderfully easy to use now. I can leave the altitude clamp open, and the scope stays put no matter how high the scope is pointed. It is a little springy but it is not a big deal. I'll refine the jig a little more to make it stiffer. But now I don't run the risk of the scope falling out of control when I loosen the altitude clamp, .

I could have made a fork mount for this refractor, but the simplicity of this jig is just so astounding I just don't have the inclination now.

There are a few things to look for in creating such a jig. First is to work out the COG of the rig you are planning to mount. This is done by fitting out the OTA with its diagonal and a heavy EP. The scope is then seated onto a narrow piece of wood and shifting the OTA along this bit of wood until the OTA is balanced on the wood.

Next is the necessary drop from the top of the tripod's mounting platform to the centre of its altitude pivot, and how far back or forward of the coupling screw it is.. The jig is then divised to drop the OTA to match its COG as closely as possible to this pivot point. This does not need to be an exact science. It is surprising just how stable the jig is even if the OTA is a few mm above or below this pivot.

Cost: $4.95 for the DIY ring clamp kit from a $2 shop
zero for the plywood off cuts I had at home
zero for the wing nuts and bolts I also had

Ease of use: Priceless

I hope this novel jig offers you some insight and solutions to some problems you may have. This jig also solves the same 'top heavy' problem with many alt/az mounts that come with many refractors.

Mental.

[alistairsam]

Nice one Alex,
Will a small counterweight at the opposite end of the wooden flat aid azimuth movement as well? At the moment, load would be on one side of the pivot head rather than distributed.
Alistair

[mental4astro (Alexander)]

Ta Alistair.

I guess a counterweight may help. Keeping the scope close to the tripod head also helps. I may look at fitting one, but I may just keep it as it is. It is easy to set up and store with a minimal amount of bits and pieces to deal with. With a heavier OTA the counter weight could be benefitial.

[MattT]

Great stuff Alex Another option is to add another identical OTA and binoview????? Love these home made bits.
Matt

[mercedes_sl1970]

Alex - it's a beautifully simple and effective design. I made one just like it some time ago for a small scope and it makes viewing so much easier.

Andrew

ps Rod Nabholz has some excellent home-built projects on his site.

[stringscope (Ian)]

Hi Alex,

Looks really good , I am glad you were able to make a practical mounting bracket for the scope.

Cheers,

[ZeroID (Brent)]

Cool idea !! I use a counter weight arm forward of the tripod tilt head on my 80 mm Achro and it works well but this looks simpler and lighter. DIY Conversion time !!!
Lends itself to doing scope\camera combinations maybe. Possibly even binoculars with a slighly longer arm extension and maybe couterweight.

[OzEclipse (Joe Cali)]

One of the best large bino mounts I've ever used was at Arthur Page's Mount Tamborine Observatory. I observed there on a regular basis during the 1980's. Arthur let me bolt down my eq mounting on a semi permanent basis. It stayed there for several years until I moved to Canberra to work.

Arthur owned a pair of WWII Japanese battleship binos. 25x125mm Nikon's. They were mounted on a counterbalanced arm so that the binos were mounted forward of the pivot point. The pivot point was lined up with the neck near the top of the observers jaw about 2-3cm below the ear. This is the point which remains stationary when you tilt your head up and down. Poke your fingers there and tilt your head you'll see your fingers don't move. Most of us who were regulars at the observatory were about the same height so adjustment wasn't much of an issue. The result was that you could stand there and elevate the binos without having to crane your neck. The azimuth was a large heavy steel wheel and bearing on a concrete slab that had a long vertical 4 inch water pipe welded to it. You could walk around the pipe turning it as you went to pan in azimuth.

The only thing that would have been better would have been a chair mounting but even as it was, it was very very comfortable to use for extended periods.

I can't visualize any way this setup could be made into a really lightweight portable bino mount for very large binos however a lightweight pair of 60,70 or 80mm bino's on a big surveyors tripod or a manfrotto 475 could manage it.

[skysurfer]

Looks great but I still miss a fine adjustment. When watching and the object is running out of the field you have to readjust the tripod in a coarse way. Or do you have a smart solution for this ?

[mental4astro (Alexander)]

Hey Skysurfer,

This thread deals with a photo tripod. But I started another thread where I did the same thing with an AZ3 mount that has slow motion controls. You'll find it here..

Thing is also with this sort of set up is mainly low power is being used, so Earth's rotation isn't such a problem. But I do understand some type of motion control is desireable at high power. You may find the way I modified the AZ3 very useful then.

Mental.