The Mounting - Your neighbors will always see it as a giant ray-gun
In the very early stages, I truly, seriously toyed with the idea of creating a modern version of one of Herschel's smaller reflectors. A non-conventional telescope requires non-conventional thinking. Well, it certainly allows you to indulge in it!
Like a small cannon in a carriage, his telescopes were bodily turned to get azimuth and then ropes and pulleys provide the altitude and fine azimuth control. Although it looks ridiculous (Ropes! Pulleys?!), it seemed obvious to me that this would have been an incredibly stable and solid mounting. Sadly though, it needed a flat, level surface like a terrace or patio to really work, and I did not relish the thought of smashing up and flattening out the backyard for one telescope!
In my internet travels I came across a website by Mel Bartels, that talked about an American instrument maker, Amasa Holcombe. Holcomb's clever solution to mounting the long reflectors of his day was to make the tube of the telescope part of the mounting. The nose is held up and guided about the sky by the means of extending arms. These work with nothing more than rope and a disc brake. Here is my interpretation on this:
The legs consist of a telescoping inner and outer section. A cord, is tied to the top of the inner section and runs down the length of the leg. It's wrapped around a pulley which is fastened to the bottom of the outer section. The cord them doubles back up the leg until it is wrapped around a bobbin attached to the top of the outer section. The bobbin is attached to a large disk. This disk is clamped by an adjustable brake-pad.
When set up, gravity keeps the leg compacted - the telescope is effectively suspended on the loop of cord sitting in the pulley. Winding up the bobbin shortens the length of this cord loop, effectively pulling the telescope up. Friction by the brake-pad keeps the mounting from collapsing back down.
The legs are attached to a yoke. This connects to the telescope though a universal joint. This is not complicated, and is made from wood and brass.
The brake discs are made from brass sheet. These are attached to the bobbin by woodscrews. The brake pads are just offcuts of brass bar (One is aluminium) with self-adhesive furniture slides used for the brake pads. Anything could work here. A bolt with a wingnut adjust the tension of the brakes.
This is the tail-end of the telescope. In an early prototype I made a mini alt-az base that the base of the scope rested in and could pivot around.
Eventually I realised that I could simplify this considerable by making a wheeled tail-piece. This meant I could pick up the nose of the scope and "wheelbarrow" it around my garden if I needed to move it. This wheeled bases does need to be anchored in place, otherwise it will slide away on you.
This weird and unlikely idea works as well as any other mounting that I've tried. Better than some! But lets not get romantic about it. Some of it's flaws are:
- The tail of the telescope needs to be restrained or it will slip away. In my case it is tethered to a stake, but it could abut against a wall, rock, have a handbrake, etc.
- Keep the base of the triangle "wide" or the telescope will topple. You may also want to have some means to prevent the legs from splaying out suddenly (I dig mine into the ground). This means the zenith is inaccessible.
- Getting a ladder underneath can be a little tricky - but can probably be improved by careful placement of where the legs attach to the tube
- It's not a mounting for sweeping or sight-seeing. (But then, this isn't that kind of telescope either). It forces you to think about what you want to see and plan accordingly, so maybe not such a bad thing!
- I haven't got the balance between the tension required on disk-brake and the force required to turn the bobbin right. This is an area that could be improved.
But for this I get an elegant self-supporting mounting that has built in fine guiding and vibration dampening time of less than a second. Setup for observing only takes the time to remove the tarp covering the scope. There is little risk of oscillation or vibration as the mounting has parts that only slide, not rotate. Gravity is working as our friend here. In fact, the universal joint on my scope has a bit of play in it, yet the scope "settles" and works fine.
To be honest, my telescope is probably at the hefty-end of Holcomb's design. I believe that for shorter telescopes (or lighter) this mounting would be absolutely perfect. In fact, I'm going to use this when I refurbish my friends 8" f/8. Although finished for now, I see this as a prototype instrument that will continue to be worked on and refined.
Edited by Meep_Esq, 13 February 2015 - 07:21 PM.