21st December 2015 Suckered again.Twice in one day!

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A glance out of the bedroom window as I rose at at 7am showed three planets to my south. I went straight outside and set up the 7" refractor on the pier only for it to cloud completely over in seconds. I never saw them again and packed up after half an hour of pointless staring at the underside of fast moving clouds as it grew slowly lighter. It was hovering around 9C, 48F so it was unusually mild for a late Danish December at 55N. The down jacket I had put on in anticipation of a chilly breeze was completely superfluous. I was soon sweating as I maneuvered the pier back to its resting place.

Then on the evening of the same day the slightly gibbous Moon was rising in the west. I dragged the pier out again from its parking place just in time for another complete overcast. Not even the slightest glow from the west!

As I had been struggling to push the big and heavy refractor up through the open tube rings one of the plywood packing segments fell out! Though this did not represent a serious danger to the telescope I immediately decided to use some small screws and nuts to fix the plywood to the rings. I also relieved the plywood packing where it was gripping the tube rather too tightly. Handy for security against the tube sliding back down while the rings were still wide open. Except that it made it all but impossible to push the telescope any higher once it was sitting in the open rings. I just hope it isn't too loose for the scary moment between placing the OTA in the rings and climbing onto a crate to tighten the lower clamping screw. The upper tube ring thumbscrew is strictly a third or fourth rung stepladder reach. An observatory or permanent, removable cover would be highly desirable to maximize my viewing time instead of wasting it on preparation and tidying everything away again.

Half an hour later I had finished my "repairs" but the Moon was still not showing its face and it had started raining! At least I shan't be troubled by loose packing rings on any of my extremely limited chances to view the sky between the endless clouds. It seems to have been completely overcast, or heavily clouded over, for literally months now. On the positive side we have hardly used any fuel in our stove so far this "winter." Each month that passes is setting yet another record for warmth.

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Next morning, it was still a very mild 44F, 7C, at 7am when I saw the sky was clear again. Having struggled to get the heavy OTA into the rings I found the tube seam was in the wrong place to allow the rings to close properly. Despite yesterday's relief work the upper ring was till gripping the tube far too tightly even when it was wide open. Disaster nearly followed as the polar axis started to rotate as I struggled to push the OTA higher and twist the whole thing into position. Working in the dark it was impossible [at first] to see the catch on the Orion stop ring was jammed against the lower tube ring!  

By the time I was set up for viewing Jupiter it had maxed out at only 30 degrees local altitude. Initial impressions were absolutely awful! The Jovian moons were shapeless and bloated with Jupiter a fuzzy, almost featureless, colourful  ball with no distinct edge. Quite why there should be any thermal effects I have no idea. The OTA's storage and outside temperatures usually match quite closely. Just as they did this morning. There wasn't a whole degree difference out or in.

Fortunately things improved quite quickly and I was able to see two distinct rings as the moons shrank steadily. The scene was one of rapid thermal agitation with only the briefest of glimpses when the contrast improved. Last night's gales had decreased but there was about a half second undulation to the view each time the wind picked up. Not enough to throw Jupiter out of the field of view nor too difficult to follow with the eye it soon damped down again.

Before long the sky turned a uniform milky white as the brightest stars rapidly disappeared from view. A very low Venus clung on the longest as only Jupiter remained visible above the house roof. There was no longer any point in moving the whole instrument to get a view clear of the roof. The strong wind was probably dragging away any convection effects from the roof  itself. I finally packed up at 8am with Jupiter now invisible having had only brief hints of potential detail in the rings. I pushed the power up to 175x but kept rotating different eyepieces through the focuser to see which would work best in the difficult seeing.

I am beginning to realise that I have overbuilt the OTA for easy carrying out to the MkIV mounting. Then having to lift it bodily into the open rings so high above the ground. The sheer size of the instrument is best suited to a fixed observatory situation. The most obvious alternative now is to make an offset Dobsonian bearing fork to carry the OTA. Freed of the considerable weight of the MkIV mounting and the heavy counterweights the pier will be much easier to move about on its pneumatic wheels.

Lowering the 7" refractor OTA into open fork trunnions will be much easier than manhandling it [at exactly the correct height and orientation] into the raised equatorial mounting rings. The sliding tube balancing weight is very handy on a finely balanced equatorial but should be unnecessary on an altazimuth. It adds yet more weight to be carried and lifted without easy provision for removal.

There will be no difficulty in bolting the base of a Berry-style, counter-weighted, offset fork to the welded flange on top of the pier. If I raise the trunnions on a taller fork it will help to compensate for the loss of height which the MkIV mounting presently provides. Viewing Jupiter at 30 degrees, with a star diagonal in place, the eyepiece was at precisely the most comfortable height while standing. This is with the present, nose-heavy balance position. A more evenly balanced OTA would provide a comfortable eyepiece height at much higher [and more useful] elevations. Re-balancing the OTA could be easily achieved with a [tool free] removable weight at the eyepiece end of the tube. Being removable it need not be carried with the OTA but applied only after the tube is safely mounted.

I shall have to scrounge some 8" PVC pipe off-cuts for the trunnion bearings and start building a fork. I feel 6" pipe will be too small to provide sufficient friction against the PTFE/Teflon pads for such a long OTA.

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