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After a stormy day it suddenly calmed and cleared by 6pm. I could see the gibbous moon in the East, with Jupiter much higher up further to the South. A brilliant Venus was so high it easily cleared the trees to the West!
I had dinner first, to allow the sky to darken and then set up the 10" on the MkIV mounting. It was obvious from the start that the primary cell was sagging on its rails. Collimation changed with each movement of the telescope. So I roughly re-collimated for each object in turn. The Moon was blindingly bright with Plato well placed but very low contrast due to the almost overhead lighting. I had a fairly constant view of the central crater and glimpses of two more. There was obvious high frequency thermal boiling on the limb and terminator. I pushed the power up to 200x but sharpness was best at 150x. I returned to observing the Moon at intervals for the next hour and half without much improvement in sharpness.
Jupiter's belts were higher contrast than usual but the three visible Galilean moons were cross shaped and fuzzy. Jupiter changed shape each side of focus. Re-collimation did not help to tidy things up.
Venus was so bright that it was difficult to focus properly. A well rounded half ball of intense brightness at all powers which I tried.
It clouded over at 9.30pm as a light frost settled on the grass. I had been crunching remaining patches of snow underfoot from yesterday's 3-4" fall.
I really have to take the primary mirror out again and fix the cell really firmly to its rails. I just needs another large coach bolt further down the cell to improve its attachment.
I now use an old, parallel sided, artillery shell casing to lift the mirror clear of its cell. I set up the shell casing vertically and just lower the cell over it. The mirror rises out of the cell until the cell base is resting on the workbench. Exactly the same technique as is used to safely lift an objective lens out of its cell. Though the lifting device needs to be well padded in that case to protect the lens surface and any coatings. The primary cell needs to be removable of in both cases. Otherwise it might involve carefully lowering a 2 metre long OTA over the cartridge shell!
The brass shell casing has the advantage of being bottom heavy and is wider at the base for superb stability. I would hate for the mirror to tip as it was being lifted. Luckily the cooling fan aperture in the cell base provided a nice big hole for the shell casing to enter. My original intention was to use a bit of PVC plumbing pipe as a lifting device until the shell casing presented itself as the perfect tool. I used to collect cheap shell casings from flea-markets in the vain hope of being able to use them for the construction of an all-brass refractor one day. Unfortunately I have only got as far as an all-brass 7 x 50 finder.
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