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With both axes partially locked I pointed the OTA gently at the patiently waiting, half Moon. I had only aligned the folding mirrors roughly by eye and the objective collimation was a complete unknown... I wasn't expecting much more than an hour's struggle with mirror collimation to achieve a reasonable result to be fine tuned with Cheshire EPs, blackening surfaces, making baffles and more hours of fine tuning.
Brightness appeared in the 32mm Plossl eyepiece and then the Moon swung into view. I struggled to focus against the focuser lock. OTA imbalance and friction made pointing difficult. I had to constantly overshoot and let it recoil. Eventually I had the Moon centered, sagging badly out of the field of view but finally in focus. I could not believe my eye[s!] At 68x the Moon was so sharp that I struggled to take in all the tiny details. Moving swiftly on to the 26mm EP, for 83x, still the sharpness held. Tiny craters kept popping into view without any effort on my part. I went up through a succession of eyepieces until I reached the 10mm for 216x. All that happened was that the image grew comfortably dimmer. The sharpness held but made pointing even more difficult. I unclamped and slid the OTA on its rails to a slightly better balance point and then spent an hour gawping at hard, black shadows, multiple mountain tops, rills, shaded contours and minute craters. Even a larger square one!
Trying Jupiter at less than 20 degrees altitude and just clear of a high hedge was never going to be a revelation. The two dark bands kept resolving and blurring again.
Dinner then interrupted the fun and by the time I returned bands of thin cloud had arrived. The formerly 'naked' moon was now surrounded in an obvious halo and a much larger diameter ring. The moment I looked through the eyepiece I knew that evening's ultra-sharp viewing was over. I checked and double checked the objective and mirrors for dewing with a torch but saw none. Soon thicker clouds obscured the stars like a high mist.
I decided to pack up for the night and reluctantly removed the objective. It was stuck fast even after backing off the locking screws/knobs. One bayonet screw clung onto the OTA plate. I tried rotating, pushing and pulling but it refused to budge. Just when it seemed I would be there all night it suddenly came free. It had obviously become too tight on the OTA plate or the 'keyhole' clearance hole was a little too tight.
Lessons learned:
The sharpest views, I have ever had of the moon, were marred by:
The MkIII mounting being badly undersized.
Despite the f/12 focal ratio I was either in sharp focus, or I was not. The focuser definitely needs slow motion. Just as did the 10" f/8 reflector.
The bayonet locking system needs minor modification for easier fitting, release and locking.
The OTA needs a hook-on weight for fitting the objective safely. Though this may demand increased but temporary, counter-weighting as well.
I need a sturdy stepladder with proper treads for safety while climbing, carrying and fitting the heavy objective onto the raised OTA. Not the builder's folding ladders, with normal ladder rungs, I use at present. The lack of proper treads offers little stability when all three hands are needed.
The adjustable height seat needs another [lower] hole for more comfortable viewing at higher altitudes. I was rather bent over for perfect comfort even with the moon at 40 degrees altitude. That said, moving to the MkIV mounting will probably set new OTA seat height requirements. Sitting to observe is both relaxing and pleasant even when struggling with an under-mounted telescope.The exposed 1st mirror collecting dew after a couple of hours exposure to freezing point. The flash shows up a lot of dust too.
The lack of baffling made observation of Orion's belt and the Pleiades very difficult due to reflected and stray moonlight. There has been no blackening of the OTA, at all, so far. A black cloth shroud should also help to exclude stray light and [hopefully] dew.
Click on any image for an enlargement.
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1 comment:
Hi Chris,
These are rare moments of sheer joy indeed, when the object being observed literally takes one's breath away - and for first light that is an added bonus. I had a similar experience with M42 when I first unveiled my folded instrument. The satisfaction is reward for all the hours of hard labour and all the fretting over designs. Now you can have fun fine-tuning to make it all that much more straightforward to set up, and chasing down the internal reflections and the sources of dew.
Best wishes
Andrew
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