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I wrote a lengthy post yesterday on options for housing my large solar refractors. Then deleted it when I had completed a new post on folded refractors. Folding my 6" optically would shrink it to far more manageable proportions.
The overlong H-alpha filtration on many modified, solar refractors is an acute embarrassment. Such a long stack makes it very hard to avoid sagging along its length. Though threaded fittings are stiffer. Most of us have to make do with push fits. Usually 2". Which is stiffer than 1.25" or T2.
Shrinking the length of my 6" makes it much easier to house. Whether sitting permanently in an observatory. Or cowering under a run off cover. Observatory size is a very serious issue. No least on price. It also eats up the garden space when this is important. As it is to most of us.
My back garden was no-man's land when I was building my foolishly tall observatories. Just to see over the hedges and my house. The latter sits unfortunately close to the southern border of my rural garden. The front garden is further reduced in width by the 7m long, lean-to greenhouse. So I have a strip of front garden only about 3.5m deep to play with.
Bounded by a beach hedge between myself and my neighbour's grassy paddock. I want to be able to push between the greenhouse and the proposed observatory. How else will I reach the glass? Besides, it is a long walk going right around the house. Just to reach the other end of the greenhouse.
I could sneak a few more centimeters if I cut down the hedge and put up a fence. Not a good idea! The fence panels would warm in the sunshine and produce strong convection currents. Right in front of my telescopes.
The beech hedge is also more natural in its rural setting. Storms could easily damage a fence. Which the beech hedge would simply shrug off. The hedge is also a useful wind break. It filters the wind rather than accelerating and directing it. The height of the hedge is now mine to choose. The birds tell me they would much prefer a hedge.
All of which brings me to the choice of accommodation for my telescopes. Let us suppose that the Pulsar 2.7m offers 2.5m internal diameter. The 2.2m only 2m Ø of clear space inside. A German equatorial mounting [GEM] swings the telescopes well off to each side. Rather than simply rotating and moving up and down like a fork mount. So it is no use [mis]calculating the required observatory size by telescope length alone. The telescope does not usually span the full diameter symmetrically.
The swept volume of the extremities of the telescope[s] is an oval [lobe] on either side of a GEM. Because of the instrument's considerable offset relative to the Polar Axis [and the pier.] If there is a long filter stack, or useful dewshield length on a refractor, then this must be allowed for.
Ideally, one would mount the telescope[s] in an open space. Then drop a weighted line from the tip of the dewshield. Or from the camera on the end of the filter stack. Then mark out the shape on the ground as the telescope is swung from east to west. There would be a vertical component, of course. At least the clear diameter required for a cylindrical observatory [and dome] will be much better understood.
The height of the telescope dewshield, as it swings upwards, is also an issue. Requiring that the telescope's height be carefully arranged. So as to be concentric to the dome's inner circumference. Otherwise the dewshield will strike the inside of the dome at certain elevations. Possibly at the zenith if the mounting is raised too high. The GEM's offset lobes to left and right must also be kept in mind. So the pier and thus the mounting height becomes vitally important parameters too.
The OTA can usually be slid along on its dovetail plate. Or through the mounting rings. Provided balance is achieved. Then a bias towards the lens or the focuser end. May help where tight clearance issues arise. Adding a weight to one end of the OTA can correct the balance if required. Though care must be given to off-centre balance problems. The balance of the telescope on the mounting may change considerably. With different telescope orientations. Causing problems with tracking. Or even motor stalls on slews.
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