Rusted

It is with mixed feelings. It served its purpose but the surrounding trees have grown since it was built. Absent neighbours, my own trees and a shelter belt. The observatory has now become an untidy mess. So removal, with a bonus garage or carport from the recycled materials, is adequate compensation.

Don't do it like this!

I have a 10" f/8 premium planetary mirror of 1/30th wave. I built a beam OTA but it twisted under the offset weight of the primary on my equatorial mount. I never did rebuild it after trying various tube forms unsuccessfully. A Berry style offset fork mounting would have avoided many of the axial torque problems but I really wanted to do high res imaging.

Whichever means you eventually use to connect and lock your sub assemblies together: KEEP IT SIMPLE. Any complication, awkwardness or difficulty will rapidly multiply over time. To become a single unit, almost unused for the rest of its short, useful life. I gave up on my folded refractor because it was heavy, bulky and difficult to collimate well from the focuser. This holds true for any long refractor. When you have a Cheshire eyepiece several yards/meters from the point of adjustment. You will have forgotten which way to turn the screw when you finally and breathlessly return to the business end. I would give every long refractor remote knobs at the focuser back plate to adjust objective collimation. BY INTERNATIONAL LAW! 😉 Be prepared to borrow ideas from other areas of your expertise and beyond. Boating has lots of nice bits and pieces in stainless steel. Avoid anything which will quickly rust. Flashed zinc is a nightmare after one winter in a damp barn. As are plain, mild steel objects like hinges. Use only hot dip galvanized, brass, bronze or stainless steel including for threaded fixings. Using zinc coated screws for anything in astronomy should be a crime against humanity! The difference in price when buying stainless steel online, from a specialist, is peanuts compared with a bubble pack from the big shed DIY chain. Commercial manufacturers have absolutely no defense for using inferior fixings when they buy in bulk by the tipper truck. So don't do it yourself!

Folded refractor? 🤫 Been there. Done that. 7" f/12.

Coincidence: Late on Sunday night ~11.45 [CET] I saw a bright but fuzzy object low in the SE diagonally below Orion. Presumably Sirius but it refused to sharpen in the couple of minutes it took to put the dustbin out. My yes were watering in the cold wind but all the other stars were nicely sharp in a clear sky. I never thought any more about it until I saw this thread. I can't repeat the observation to confirm it was Sirius tonight because it is wet and cloudy. My view of the sky in this direction is usually blocked by trees. I was at the far end of my 80m drive at the time. Where I had a clear view all around. Even to the east.

You could do a hell of a lot of damage with that tool! 😱 I can't imagine anybody surviving within the blast radius! That means firmly fixing down your work-piece and standing well clear. Like several hundred meters away! Preferably switching it on and off from across the field behind a sandbag barricade! I doubt the chuck will remain in place for a microsecond with the loads being applied! Where a ring is too large for my vintage lathe I just use a small power router with a circle cutting jig and high quality router bits.

Agreed. I wasn't expecting the OP to take the idea seriously. They would have to be in the desert to capture anything against truly dark skies. Is that how you spell it? It been half a century...

A possible [silly] option would be a "lenseless" Schmidt camera: You build an extension to the main tube to house a diaphragm slightly smaller than than the aperture at twice the focal length of the primary. RofC. Then you build a curved film holder at focus. You load a single frame of film in the dark and then put a light tight cover on the film holder. You go out to the telescope and load your film holder. Then remove the cover to take your exposure. You'd need a driven equatorial mount of course. The patience of a saint and the ability to develop and print all your failures is taken for granted. A fast primary has a very short exposure time with film before sky light fog ruins the shot. You could use a modern astro camera with a correcting lens right in front of the camera. A plano-convex I think. You'd have to play around with different power lenses until you corrected the spherical aberration. Or get a tame optical designer to run OSLO. Or whatever they use these days. I am with those who say leave well alone and use the whole telescope as it is. IF the images are acceptable to you. Nobody else matters. The curves on corrector plates are quite small. So the corrector is weak optically. There are chapters in "Telescope Making" on making SCT correctors using oddly shaped ring laps with petals shapes in pitch. Commercial SCT corrector lenses are made by using a vacuum and polishing the glass flat. Once the vacuum is released the corrector takes on the special form. No doubt this can be made semi automatic for those with the factory resources. There are few amateurs on the planet who can manage a 14" optical flat. Let alone produce a corrector! There would be endless testing as you crept towards a polished corrector lens. I certainly wouldn't be starting from there with no previous optical working experience. Where would you buy a new corrector glass blank to start work? It's not window glass!

The tube was a common [or garden] PVC drainpipe. I replaced it with a laminated 1mm marine ply tube of two layers. Ultralight and stiff. I now use dust extractor tube in thin, galvanized steel. A single straight seam rather than spiral. Stiff and lasts forever. Available in many diameters and two meters long.

I can't remember if I responded to your last thread. I have two iStar objectives. Both excellent. 6" f/10 H-alpha. 7" f/12 R35. I built a offset/counterbalanced Berry style mount for my home made 5" f/15 back in the 1980s. Whereupon I discovered that the push required was almost perfectly matched in all directions. Until I reached the black hole near the zenith. Then things became distinctly sticky. I also discovered that unwanted twisting of the tripod legs caused backlash. I used 2" scaffolding tubes for the legs. The weakness lay in their connection to the head via simple angle brackets. I suggest a substantial pier if it is at all possible. At least 6"/15cm diameter.

You are a saint Sir. 😇

Forgive me Pete for I have sinned: [Grossly overdone just to see what was hiding in there.]

I'd aim for a worm and wormwheel drive. This guarantees locking at every point in the entire travel of the slit cover/shutter. The downside is the relatively slow motion of the load compared to bevel gears. Though multiple start worms can increase the speed of travel. A major advantage of a worm drive is the light load on the operating handle. Allowing the elderly to manage the load easily if they have the stamina to keep winding. It would probably require major surgery to halve the slit cover/shutter and make it travel horizontally on rails. EDIT: If you must go with a boat style winch ensure it is approved for heavy lifting purposes. These are a safer option but more expensive. An electric winch is an even safer option but at even greater cost. They are great fun for being effortless in use. Then there's the manual chain hoist. This could be incorporated but would probably need the chain hanging down from the top of the slit. Here, quality matters. Dirt cheap hoists from discount, big shed sources could literally fall part! As did mine! If you have any doubts about your mechanical skills I would find somebody who can design and manage the project safely. A dome that size has a heavy shutter! Amateur astronomer's lives matter!

Given the narrow bandwidth this could decimate the expensive and "variable QC" solar equipment market. From the phone and tablet images I am assuming it can be scaled up by adding a larger refractor. If not immediately then it will soon become standard equipment for solar imaging and observation.