10" f/8 March madness on the Moon and Jupiter.

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Clear skies and the Moon sharing the sky with Jupiter high above drove me to get the 10" F:8 out again. Clear skies with bright moonlight and no wind at all are very unusual.

I fiddled about with the collimation until I could use 200x on Plato. I was able to glimpse the central crater at all powers from 100x upwards. I even ran a long cable out to the (noisy) mirror fan from a 12V model train transformer. It made quite a racket at first but then settled down. The fan was blowing forwards around the mirror from the rear opening in the cell. I cannot say that it made any other visible difference except applying micro-tremors to the image. I tried reversing the polarity but the motor would not start. I need to look into this problem in daylight. Reversing the fan physically within the cell is not an easy task since the primary mirror has to come out.

My larger collection of Meade 4000 eyepieces seem to be anything but parfocal across the range. They have a mix of "Japan" and "China" markings so that may be the cause. As I didn't need to be dark adapted for the Moon or Jupiter I used a diode torch to select eyepieces from their new case. Which I had placed on the mounting base slab under the angle iron stand.

I have added 10mm closed cell foam to the little partition boxes to raise the eyepieces to an easier level for removal and replacement. The partitioned boxes were too small to allow any more foam to nestle the eyepieces properly. I don't think  this matters too much since they are not subjected to long journeys in the car. Thanks to the handles moulded to both top and bottom of the the case it is very unlikely to be lifted in any way which would tip out the contents onto the ground.

The range of powers has been re-ordered to make selection easier in the dark. Lower powers to the right. Higher to the left. The hinged lid is handy because it drops down automatically to protect the eyepieces from dew. Not bad for under £3 equivalent. Using a very deep, padded box, with the eye lenses facing upwards, doesn't make much sense to my fuzzy logic. I can use the comparison of length to sort them easily and quickly. The Dyno tape markings on the lid are easily read with a torch to confirm which power I am using. It is very easy to see which lens is in use from the empty partition. It would have looked tidier if there were far more partition options but beggars can't be choosers. Having used a deep, plastic storage box for my eyepieces for years I much prefer the new arrangement. All the extra space around them makes them easier to lift out and replace in the dark.

I struggled again to focus quickly and accurately with the simple Vixen focuser. Since I wanted to avoid physically exciting the OTA with my focusing efforts it required great care not to shake the desired object out of the field of view. I can now see why slow motion knobs are so popular. The rack and pinion focuser does not offer the tiny adjustments or sensitivity in focus required at higher powers.

Despite being F:8 the telescope is either in focus or it is not. There is no "refractor like" softness in best focus. The greater flexibility and leverage of such a long OTA does not aid focusing when the image has to "die down" between every touch of the focuser knob! Focusing was far easier on the Moon than Jupiter. Jupiter had four moons on one side. With two moons very close together which changed rapidly in the two hours I was out there. The moons themselves looked like kids (poor) drawings of stars. So the collimation was still way out. Jupiter defocused to into a triangle of three offset blobs! Though I could still see some detail in the belts.

The mirror cell continues to irritate with its sloppy and sticky collimation adjustments. Undoing a wing nut almost guarantees it will go slack. Trying to tighten one often feels as if it is fully tightened. The spring pressure is probably just not enough to support the weight of the primary mirror. Last night's observations were cut short by completely losing the collimation while trying to fine tune it!  

I have promised myself that I would solve the mirror cell collimation problem but haven't. I haven't fixed the flexibility of the mirror cell pot either. There is always an element of inertia to completely undo previous construction and start again with a potentially better design. As the Irish are supposedly fond of saying: "I wouldn't have started from here." 

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