The last time I wrote about my astrophotography attempts, I came to the conclusion that my biggest problem was the mount. My current rig perches atop a surveyor’s tripod, which is more than adequate for visual work but not as rigid as I’d like for photographic work – it vibrates a little too easily for my taste. Besides, any portable setup is going to require polar alignment every time I want to use it, and to do it properly can take hours out of my evening. The traditional approach is to build an observatory, but I’m renting my home and I’m not sure how I feel about building on somebody else’s property. Besides, that costs money which I don’t have.
So I’m going the cheap route: I’m sinking a pier into the ground at the same spot in my garden where I usually set up the tripod. The plan is to dig a cubic hole, about 60cm on each side, drop in a pole I have lying around (about 20cm diameter, 1.8m length), and then fill it in with concrete, leaving the last 10cm for soil so that the lawn can grow back in. Once the concrete is cured, I’ll build an adjustable steel plate on top with mounting bolts to accept my equatorial wedge. Then it’s just a matter of assembling the telescope on top of the pole, taking my time to perform a nice accurate drift alignment, and welding the plate down to lock in the alignment. The wedge itself will still be free to detach, so that it doesn’t have to stay outside in bad weather, and can still be used on the tripod for when I want to travel. When not in use, the plate will be topped with a sundial, to transform it from an ugly pole into a useful bit of garden furniture!
I’m not sure how stiff this mount is going to be, but I figure it shouldn’t be bad – it’s set into a significant mass of concrete, and there’s only 1.2m of pole protruding upwards from the ground. Having it made from wood should hopefully help to damp vibrations, and the thickness will hopefully translate to good stiffness. And if it’s not as stable as I’d hoped, well it’s only cost me the price of a few bags of concrete mix. And when I move to another home, the landlord only has to cut the pole at ground level to restore the garden to its original state! So far I’ve spent about 4 hours digging (spread over weekends), and the hole is not done. Partly this is because it turns out that we’re on very rocky soil (I’m casting rocks onto their own pile separate from the soil, and the rock pile is higher), but mainly it’s because there’s one very large rock almost square in the middle of the hole. The portion I’ve uncovered so far is a hunk of quartzite, about the size of a toddler, and I have no idea how far it extends horizontally beyond the south edge of the hole. I’ve attempted to crack the rock by repeatedly smashing a sharpened length of I-beam onto it, and I’ve tried chopping a groove into it with the spade. These approaches worked quite efficiently on the rest of the rocks, reducing them to gravel fairly quickly, but quartzite is hard stuff. I will probably have to move the hole about 30 centimeters to the north, since it finally occurred to me that even if I do crack this thing, I’ll never be able to hoist it up and out of the hole!