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Thursday 11th 49F, heavy overcast rain and drizzle.
A four foot builder's level provide the extended weight on a double plumb line. I ensured it was level and marked the body to ensure the measurements were the correct distance apart. The parallelism was, quite surprisingly, within a few millimeters. Though it didn't help me to get the shutters moving smoothly.
I added another batten to push the base of the shutters outwards. Which meant I needed a taller support for the lower drawer slides. Hours later, after much fiddling it was finally lunch time. Still no real progress. The shutters are clearing the dome but still sticking.
Three more hours in the afternoon. Drizzle teased me for a while but I carried on. Using the plumb line reference bar I had the lower drawer slide within a couple of millimeters of parallel. I replaced the smaller, drawer slide support with the original 2x4. Then I used the rangefinder to confirm the observation slit is central and marked the center on the base ring..
Packing under the shutter allowed me to raise the drawer slide form inside the shutter. I then re-attached the drawer slide to the form and the 2x4, made it level and about an inch higher than before. Now I have plenty of clearance from the dome. It still made no difference to the sticky shutter movement.
I was working by LED floodlight by the time I gave up for the day. The shutters are proving very frustrating. The problem may well be their length and flexibility. I can push the shutters closed from the ground outside with a long length of timber. Not ideal when I need them to work effortlessly from the inside the dome when the skirt is 4m from the ground.
The shutters on the old plywood dome aren't that much smaller. It is just a matter of scale. They have worked fine from first fitting. It was just a matter of getting the shutters moving as one. I would pull them as high as I could reach from the observatory floor. Just to overcome the inertia. Then they slid smoothly open and closed.
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2 comments:
HI Chris,
Thansk for sharing this great blog with tonnes of information. I'm also working on (rather designing) an observatory) and I found your ideas about elevating the observatory very useful. Do you also notice an improvement in seeing (and less dew) when doing nighttime astrophotography or is is most prominent during the day when doing solar imaging?
Best wisghes and clear skies,
Hans (from the Netherlands, so pretty much the same climate)
Hi Hans,
I had decades of poor seeing from the ground but that was only ever for visual. The main reason for raising the observatory was to be able to image the sun over tall hedges. I have certainly enjoyed better average seeing from being up high. Though I never really did any imaging from the ground. Now I only rarely do visual.
You still need to provide a solid support for the telescope mounting. Not easy for a raised observatory. Chimney blocks make a good solid pier but will require a very big, concrete foundation block.
I made my very tall 4.2m high, pyramidal pier from 100x100mm timber legs. Clad in 18mm plywood for stiffness. This massive pier rested on four, pre-cast concrete, carport foundation blocks. The pier has worked well for three years provided it is isolated from the observatory structure.
Good luck!
Chris
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