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The lengthy diatribe on mountings for classical refractors covered the basics according to my own opinions. Mostly it was more thinking aloud in an attempt to fix where I could make rapid progress. All such mountings would need to be portable to allow free movement around and even outside the garden.Hanging the ventilation pipes from the MkIV, on its pier, had allowed me to judge the required height for any other mounting I might build. The German mounting lowers the eyepiece when the tube is pointing high on either side of the mounting. An offset fork, altazimuth does not lower the eyepiece more than the radius from the altitude pivot center. An inverted, counterbalanced fork actually raises the tube when at lower altitudes. Not the least bit desirable when that means a stepladder is needed for even quite modest altitudes.
I like having equatorial drives because they suit my taking astro snaps of the Moon and planets at the eyepiece. An un-driven mounting needs constant nudging to bring the object to the center of the field of view. Acceptable for visual use at modest powers but not ideal for photography.
With an equatorial drive one can leave the telescope to download images from the camera. Then return in the relaxed expectation of the object still being in the field of view. Handy when trying different camera and eyepiece adjustments and trials. The camera rarely captures exactly what one sees with the naked eye. The eye is far more forgiving of image centration, vignetting and colour error. The camera will often capture purple fringing which my eye cheerfully ignores.
I have long planned to build a raised observing platform on the gable end of the wooden workshop. It would be much like a carport but with a solid floor to stand on and a safety rail to stop me falling off. Such a platform would be unlikely to be stable enough to support a pier and an observer without at least some shaking.
How to avoid exciting vibration with observer movement? The obvious answer of a very tall, steel pier passing through the floor is a non-starter. It would need to be massive not to flex. The foundation would need to be huge. Worse, it would place a vertical pipe right in the in the middle of the carport. So parking or working under cover would be difficult to impossible.
The pitched roof of the massive shed could support a north bearing for a yoke or cross-axis mounting. Though it might need an extension to raise the bearing high enough above the platform floor to allow the observer to reach the eyepiece when looking south. The south bearing could be extended out to the edge of the carport structure. Though a separate support post rising from the ground would be much better from a vibration point of view. But, now the new post is blocking access again. A "goal post" form of construction could support the south bearing isolated from the platform structure.
Or a deep beam could jut out from the shed's gable end being supported on the shed roof timbers. A vertical pier would rise from the cantilevered end. The beam would have to project from below and remain clear of the platform floor construction. The pier would be isolated from the floor as it rose through a clearance aperture much like an observatory with a wooden floor.
How much such arrangements would suffer from wind movement of the shed itself is an unknown. I could fix a small mirror to the gable end to check for movement of the reflected view through a small telescope. The mirror would effectively double any vibration by optical leverage. The shed is fairly well protected by all the high hedges and trees. Which is entirely the point of building a raised platform to be able to see much more of the sky.
In an ideal world an observatory dome would be built on the platform. Apart from the high cost, this would still need a solid mounting support. One preferably isolated from the floor of the platform. A yoke or cross axis would not be an ideal choice in that case. Something much more compact would be required to avoid filling the dome with the mounting itself. Though a roll off roof, moving towards the north when opened, has potential. The shed could be easily adapted with rails on the existing roof. Though I would much rather have more shelter from the wind in the bitterly cold Danish winters. The gable end of this roll-off roof could be foldable at the peak to allow lower elevations.
A barrel vaulted structure could be split in the middle. To allow each half "roof" to move east and west on rails with a hugely variable slit width. This would provide more protection from the wind with reduced thermal effects over a normal, hemispherical dome. Though this option might block the view directly east and west unless the halves were provided with rather long rails. A rotating semi-cylindrical 'dome' with a horizontal axis and wide [sideways moving] shuttered slit has some potential. Up-and-over shutters are more amenable to blocking bad weather from entering the "observatory" than sideways moving.
A trip to town, to buy some black 12mm, closed-cell foam, camping mattresses proved frustrating. The website said black only. The stock was pale grey! Not to worry. It will probably look acceptable as packing between the pale green metallic, painted rings and the silver-grey galvanizing of the tube. The advantage of these Vixen rings is the provision for a fixing on either side. They could be used with side plates to easily make a Dobsonian bearing for altitude on a Berry, offset fork mounting. Or, another, fairly large refractor could be bolted on top of the main instrument. For use as a serious finder or as a long focus guide 'scope.
Click on any image for an enlargement.
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