10" f/8 Jupiter & M42.

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Jupiter was already at a good height when I trundled the tube out to the MkIV mounting on the lawn. The problem is that every such journey throws the collimation out again. I tried inserting the Cheshire eyepiece but it isn't easy to use in the pitch dark even with a diode torch. Alignment was well out and the curved vane secondary holder and my rather clumsy mirror holder really don't help.

I have bought a dirt cheap storage case for my enlarged selection of secondhand Meade 4000 eyepieces. Simple Dymo labels on the lid show the power in the 10". I am experimenting with foam padding but unhappy with results so far. These are a mix of Japanese and Chinese made Meade lenses. 32, 26, 20, 15, 10 and 6.4mm are now present. The 2x Barlow provides intermediate powers if desired.
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Eventually there was reasonable optical alignment and I could try the telescope on Jupiter. Though the two major belts were clearly seen there was little extra detail. There was the usual drama of trying to turn the focuser knobs while the image shook. The 10" is a real jelly compared with the 6" refactor. The latter is rock solid on the MkIV mounting.

For the next couple of hours I tried a number of eyepieces without improving the quality of the image. I had connected the power supply and paddle to the drives though I made little attempt to align the polar axis. It was pointing roughly north and that was all that mattered for following a planet for visual use.

Then I tried the telescope on Orion's Nebula M42 and was astounded at the detail visible using 32mm and 26mm Meade 4000  eyepieces. The 26mm was best at 77x for its improved contrast with the darker sky.  I felt I could actually see the wavy surface of the nebula. The gas clouds stretched to the edge of the field of view with deep black notches and widely extended wings. Better than I ever remember seeing it before in any instrument. This was despite the rather low altitude of the nebula. Dark skies obviously help here. 


Note the coincidence between spaces available and components to be fitted. Unfortunately there is no real choice as to where the yellow spacers may fit. So there is a little too much room in some places. An Orion 2x Barlow sits at top right alongside the Cheshire collimating eyepiece. The simple digital camera nose/eyepiece centering adapter is the bright blue object sitting at the bottom left. 

The intensely bright ISS went over at one point. I watched it through my 10x50 Zeiss binoculars but no detail was visible. A surprising number of satellites passed through the field of view wherever I was looking with the telescope. It must be getting quite crowded up there!


I retired indoors for dinner at 8pm and returned an hour later to much mistier skies. Finding a bright star overhead, I tried racking through focus to compare the infra and extra focal images. At least they were similar, round and fairly sharp edged. Orion had disappeared behind the roof but Jupiter was now very high.

Unfortunately the image had not improved in the three hour's exposure of the mirror to the night air. It lives in unheated accommodation anyway so its thermal differentials should be quite small. I have not yet tried the 12V cooling fan which I fitted to the mirror cell. There seemed to be little or no thermal agitation of the image this time. Previous observing sessions were plagued by tremors.

The orange, near full moon was just climbing above the horizon as I packed everything away again. It would be hours before it rose over the hedge. If at all. Everything was now saturated with dew.

As mentioned above, I have bought a few more secondhand eyepieces and a cheap plastic case to match the longer focus of the 10". With powers being 2/3rds greater compared with the 6" F:8 I had no useful range of magnifications except for the dirt cheap lenses which came with a £70 70mm Bresser refractor from Lidl.

I have Dymo labelled the case lid to make finding the correct lenses easier. The Meade text is impossible to read without donning reading glasses and using a bright torch. No doubt I shall eventually remember the magnifications available from each eyepiece. Note how the carrying handle is moulded in both base and lid. So the contents are never likely to spill out while being carried. Not even if I forget to close the snap locks. Some of the small, alloy storage "suitcases" are very vulnerable to popping open.

I really need to obtain a laser collimator to sort out the alignment more quickly and positively. I may yet fit a four vane spider to overcome the weaknesses of the curved spider. I may also fit a square section tube to the OTA to provide an extra degree of rigidity and somewhere to mount a finder. A slow motion focuser would help too. The short range of good focus was a complete surprise after using refractors for so long. The 10" is either in focus or not. There is really no leeway despite it being a long focus F:8.

I also intend to make a simple, plywood, counterbalanced, offset fork mount for the 6" refractor with Dobsonian bearings. I need a reference to compare the seeing through the 10". The fork can sit on top of the heavy steel pier to provide visual comparisons with the 10".

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