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A Novel Alt-Az Mount for a Rich Field Telescope


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A Novel Alt-Az Mount for a Rich Field Telescope

Most of us have had the desire to take a break from using the average telescope with its relatively high power and concomitant narrow field of view and difficulty in finding targets. The so- called rich field telescope or large binoculars seem to fill the bill with their low power and wide fields. The question then becomes how to mount the thing for comfortable, extended viewing. Binoculars with their ability to use both eyes seem attractive until you consider the elaborate pantograph type mounts required to hold them in front of your eyes. I wanted a design that limited the eyepiece movements to a minimum so I could remain seated in one spot for an extended period of time.

The design I hit upon is shown below.

It was designed for a 5” F/5 refractor. You will notice that the tube is attached to the mount at a point far from its balance point necessitating the counterweight. This is to place the eyepoint on the vertical azimuth axis giving a small excursion of the eyepiece without having to use too heavy a counterweight.

Using standard 2”Sch 40 pipe fittings meant ease of assembly and kept the price down. This is a good size to use as they are more common than 1 ½ or the more expensive 3”. They can often be found used at plumbing shops. It also meant that there was only 4 machined parts. These are the tees that are the bearings and their mating nipples that rotate inside them that form the alt – az axles. The rest of the mount is pretty much self explanatory. Machine the nipples first, shaving off just enough to create a smooth round surface leaving as much of the threads as possible. They might leak if filled with water under pressure but who cares? Measure and bore the tees leaving much of the internal thread to retain grease. To make the pier I welded the pipe flange holding the Az axis to an old 6” pipe which was then welded to a used disc blade. It makes a stable pier if properly set. A more elaborate setup would be to sink the pier in concrete and build a rotating chair arrangement that could circle the pier as the telescope moved in azimuth. I have just never got around to doing this but it would be worth doing I think. It was built more than 20 years ago and has been out in the weather ever since (as you can tell from the grunge) and still functions as it did when first made.

A word about the telescope might be in order. At 625mm fl it has a 32mm fl military Erfle giving 19x with about a 3.5 degree field and 5mm exit pupil. It has an Amici prism instead of a diagonal giving a right side up and left to right field while folding the rays 90 degrees. I did this because I could then compare the field directly with star charts. It is quickly attached and detached with two captive bolts that are wing nutted to the piece of 5” aluminum channel.

Other than the rotating chair idea this mount leaves little to be desired for casual sky gazing or determined comet hunting.

 

– Jan Bentz -- mrtoad33@gmail.com


  • jtsenghas and davejlec like this


7 Comments

Nicely and simply done! An added advantage of your design is that the eyepiece is very close to the altitude axis, so your scope should be very insensitive to large changes in eyepiece weights. This is particularly important for low power viewing, for which very large eyepieces might be used.

A variant of this design with the scope further from the pier would make an excellent mount for those whose mobility is limited, in my opinion.

Well done!
    • jrbarnett likes this

Excellent. Maximized simplicity. Prob'ly last forever too.

    • jrbarnett likes this

Most of us have had the desire to take a break from using the average telescope with its relatively high power and concomitant narrow field of view and difficulty in finding targets. The so- called rich field telescope or large binoculars seem to fill the bill with their low power and wide fields. The question then becomes how to mount the thing for comfortable, extended viewing.

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You have me thinking I might like to pipe mount my 6" f/5.9 achromat.

 

Thanks for the great article.

 

Regards,

 

Jim

I have hunted through old bookmarks but doesnt look like I tagged it .... I saw a dude on a forum or website somewhere who had a reclining chair - like those old folding wood recliner chairs which have one slung/curved piece of fabric to park your b*m on and lean you back on all in one piece. Only bolted to the two side wood supports of the wooden chair frame he had attached a PVC contraption which held his bino's suspended about eyeball height. There was no counterweight if I remember rightly, just hand tightening some PVC rotating joint by hand. Each of the four legs ground contact points had two small castors offset so they sat on top of a circle of aluminium pipe so he could sit and push with his feet to rotate around. Chair folded flat and its shoulder strap went through the aluminium tube circle to carry the whole sheebang over his shoulder. Can't find the thing on Google, but I guess you get the idea from what I am describing. It was neat. Reminded me of those WW2 gunners who sat on a laid back chair sighting up through the sights and turned a crank for the whole thing to swivel around on its base. Only this guy pushed with his feet and stared up through suspended bino's hanging off the chair back. 

Great idea, Jan!

Photo
Robert Ayers
Jul 12 2016 11:52 PM

Thanks for the article.  I too decided that the way to go for a low-power telescope was alt-az with the scope moved forward so the eyepiece stayed relatively fixed. 

My scope was the December 2006 article in Gary Seronik's column in Sky and Telescope. 

You can read that article at

www.RobertMartinAyers.org/SandT-December06.pdf

Photo
Edward Swaim
Jul 14 2016 05:17 PM

Here's info on that bino chair: http://www.cloudynig...r-chair-photos/

I have hunted through old bookmarks but doesnt look like I tagged it .... I saw a dude on a forum or website somewhere who had a reclining chair - like those old folding wood recliner chairs which have one slung/curved piece of fabric to park your b*m on and lean you back on all in one piece. Only bolted to the two side wood supports of the wooden chair frame he had attached a PVC contraption which held his bino's suspended about eyeball height. There was no counterweight if I remember rightly, just hand tightening some PVC rotating joint by hand. Each of the four legs ground contact points had two small castors offset so they sat on top of a circle of aluminium pipe so he could sit and push with his feet to rotate around. Chair folded flat and its shoulder strap went through the aluminium tube circle to carry the whole sheebang over his shoulder. Can't find the thing on Google, but I guess you get the idea from what I am describing. It was neat. Reminded me of those WW2 gunners who sat on a laid back chair sighting up through the sights and turned a crank for the whole thing to swivel around on its base. Only this guy pushed with his feet and stared up through suspended bino's hanging off the chair back. 



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