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The sky cleared in the late afternoon for the first time in ages. I immediately set up the DIY iStar refractor on the Fullerscopes MkIV mounting. The temperature in both storage and out of doors had been virtually fixed on 50F, 10C all day. It had rained almost continuously all morning but with lighter showers, on and off, all afternoon. The pier on its pneumatic tyres becomes increasingly easy to move to a suitable spot for observation. A true revelation in mobility compared with the former solid casters constantly sinking into the lawn.The slightly gibbous, half Moon was just rising over the 8' high, eastern hedge when I first started looking. Strong thermal tremors were visible on the Moon's image and were never completely absent for the next hour and a half. Plates of often thick cloud kept passing over and obscuring the moon to some degree. The long periods of darkness gave me plenty of time to adjust the collimation. Which had proved to be very badly off. Both the focuser and objective were not remotely centered on each other! This is something I could have attended to in advance without putting the telescope on the mounting had I checked.
So I brought out the Cheshire alignment "eyepiece" and a small LED torch. First I roughly centered the cross-hairs of the focuser axis on the center of the objective. Then fiddled with the objective cell screws deep inside the huge dewshield. Eventually I had squashed the line of three, star-like reflections, back from the objective surfaces, into almost overlapping each other. I really do not like the cross-head screws I used for the collimation adjustment! I shall be changing them to hex socket screws ASAP if I can find them long enough!
The dewshield/counter-cell started off much too close to its supporting, plywood rings. So that screw adjustment had little or no effect. It was only after I slacked off the "pull" screws by a several turns that I was finally able to get some positive adjustment with the "push" screws.I need a much longer tool for the collimation screws because they are so close to the dewshield's inner surface despite its 10" diameter to the 7 inches of the objective. My fingers holding the screwdriver kept rubbing on the inside of the dewshield an blocked my view of the screws. Though there was no danger of damaging the objective glass thanks to the small torch and very careful technique. There was a risk of cosmetic damage to the cell flange due to the poor location of the screwdriver in the cross head screws.
The colour correction at focus [on the Moon] was very different from my 6" f/8 Celestron CR150HD refractor. The usual purple wash in the shadows and on the limb were completely absent to my eye. The still, very low Moon looked monochrome but faintly "warm." A very [very] pale orange-buff which might well have been the result of the Moon being so low. On the limb there was a very narrow, dark, greeny-blue border spilling into the dark sky background. Depth of sharp focus was nicely short but I could not describe it as razor sharp under these observing conditions. Light levels were comfortable at all powers in my right eye. In my left it was the usual "untrained" glare at lower powers.I have never taught myself to use both eyes and their sensitivity to light is very different from each other. My right eye even feels as if it has ND filters compared with the right.
I concentrated on Plato which was well placed quite near the terminator. There were no minor craters visible but that is hardly surprising with the collimation still off. Not to mention the thermal waves constantly wrinkling the Moon's image. I kept pushing the power upwards with shorter focus eyepieces until I had a 12.5mm for 170x then finally the 10mm for about 216x. Each Mead 4000 Plossl eyepiece from 32 to 10mm needed refocusing.
The scale increased dramatically at the "short" end of the series but it was an unfair struggle when the Moon was so low in the sky. Even hovering over a neighbour's large roof at first. According to Stellarium the Moon had only managed to climb to 20 degrees altitude while I was still outside. So, while it was nice to have the familiar moon as an easy target it should not be thought of as a critical one for seriously testing the new lens.
I did not use the 2" star diagonal but had fitted the two [2" fit] extension adapters, in series, for a "straight through" view. There was quite a degree of slack in this set-up due to a lack of cut-outs for the individual clamping screws. Which meant that the numerous "sockets" and "plugs" were not [remotely] fully seated. Not ideal [at all] and I may well have to attack these shiny new extensions with a file to make slots for the clamping screws. The 2" dielectric star diagonal has a proper slot provided for the 2"-1.25" adapter screw which ensures a close fit without play.
The Fullerscopes MkIV mounting felt solid and smooth and had coped well on feel and balance. Though it took a few seconds to settle down after each touch of the focuser knobs. Acceptable but slightly irritating. A Hargreaves strut might be the answer here. The 8' length and 40lbs weight of the new OTA obviously takes its toll on the old mounting. Damping time is all but instant when supporting the [stumpy] 6" f/8 Celestron refractor. I did not connect the drives last night and found the experience interesting. I realised that my hesitation to adopt an altazimuth mounting for the iStar lens was not as black and white as I had previously supposed. A gentle nudge, even at 200x, was easily enough to give me time to examine the image before it slid from the field of view. The advantage of a drive is that the object is still there after several minutes. Or even for as long as it takes to go indoors to download the latest images. I don't own a laptop.
The heavy sliding weight, on its long bar on the OTA, is really excellent and really needed due to the very long moment arm. Particularly when using the two extensions and the mounting's shaft locking screws slackened right off. I had fitted a plastic plug to the weight clamping screw and this gives an excellent feel. Without it there was a strong sense of being tight or loose with no latitude for safe movement with a nice, silky level of friction and control. Balance is vitally import with such a log OTA and the weight does its job even when the OTA was not initially placed for perfect balance in the tube rings. When I discovered the objective end wanted to sink I simply slid the weight to the focuser end of its travel and all was well again.
The OTA is still tight in the plywood packing rings and obstinately refuses to slide easily. Which is handy insurance against the OTA coming unstuck during fitting and removal. Though it does make it hard work to push the tube through the rings for balance. Fitting the heavy OTA starts with the declination saddle vertical and both axes locked. The OTA is lowered into the lower tube ring to safely locate the main tube. Then the OTA can be tipped up at the focuser end to drop snugly into the top tube ring. The OTA is then completely safe while I climb the stepladder to tighten the top ring clamping screw. The lower tube clamping screw can then be tightened at leisure. It is only just reachable from the ground.
With the Moon at 20 degrees altitude I was comfortable just standing at the eyepiece. Though I leaned an elbow on the stepladder for greater stability. Rather than holding the focuser to remain fixed and relaxed at the correct distance just behind the eyepiece.
Eventually the last, few bright stars disappeared and the Moon had gone completely from sight. There was even a very light shower from a dark grey sky. With no sign of clearing I packed everything away and went in for dinner. When I glanced out again at 11pm the sky had cleared completely. With a low, still slightly orange Moon, glaring through a misty halo just above the neighbour's trees.
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