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Sharpie graciously offered his assistance a couple of nights ago, and we were able to ascertain that the laser reflections within his TOA did not select to the central spot of the focuser either, although they were within less than 1 cm by eye, and closer to the centre than mine were. Sharpie advised that he does not photograph through it, but his scope performs very well visually.
This seems to infer that maybe there is a range within the collimation adjustments that returns acceptable viewing results. Maybe there is the one perfect setting, but around it a region of acceptability .
Armed with this information I decided to have another attempt to align the central reflections better than what I had. Mine consisted of one major reflection about 1.5 cm from centre at 12 o’clock position, and another lesser on about 2 cm out at 10:30.
I again completely removed the lens assembly. Initially I checked the reflections with just the front element removed and I was greeted with an asterism of a three dot pattern. One fainter dot up at an 11 o’clock position and two brighter ones at about 3:30 and 4:30 position but closer to the centre.
As another source of confusion, I noted that when I held the assembly(only the two rear elements) against the mounting plate, and rotated it, the asterism did not rotate with the assembly. As I rotated, the asterism moved around as a whole with a small circular motion, but did not itself rotate.??
I rotated the laser source and racked the focuser in and out, but it had minimal affect on what I observed.
Not to be put off, I removed the rear element and replaced the assembly (with just the central element now). I noted a single returned reflection not far from the centre.
I used the adjusting screws to centre this reflection, and now noted that when I rotated the whole assembly, this central dot remained in place.
I then replaced the rear element, and noted again that I had a three star asterism again, although the two brighter reflections were much closer to the centre now. Rotation the whole assembly produced the same result as before. The asterism did not rotate but moved (now slightly) as a whole around the centre.
In an effort of completeness, I removed the rear element, and rotated it 90 degrees before replacing it. The affect on the observations was again minimal. I rotated it a further 90 degrees and again minimal change (if any).
Convinced that the rotational placement of the rear element has no major affect on things, I replaced the assembly into the OTA and secured it with the mounting screws.
Now I loosely held the front element onto the assembly, and noted that I now had my major reflection very close to the centre of the focuser. Rotating the front element had no affect on location of the reflection.
I fixed the front element back on with the mounting screws, and then went through the fine alignment with the artificial star.
The settings for the adjusting screws were not far off, and I quickly achieved alignment again. (5 previous days of practice helped too).
With fine adjustment set, the laser major laser reflection is within about 4 mm of the centre. The earlier second and fainter reflection is no longer visible.
Although the sky conditions were not good last night, Star tests showed the scope appears to be working well. I managed to visually split a 2 arcsecond double star despite the unstable conditions.
I’m quietly confident that I now have the scope back to better than I have seen it before. I have demonstrated to myself at least that it is possible to completely strip it down and rebuild it with minimal equipment. Artificial star and Howie Glatter laser collimator.
I’m still to work out how to get iPhone pics small enough to post here.
The words of my father echo in my brain,
“ you’ll never know if you don’t have a go”
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