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I wish I could report an update by now but the weather has been
horribly cold, cloudy and very windy simultaneously. It was 23F, -5C in
my workshop and I'd rather not let my breath condense all over
everything. Just handling metals even in grippy, industrial gloves is
unpleasant at these temperatures. Just putting the gloves on in the
first place takes some stoicism if it quickly leads to fingers aching
with cold. I do have a variety of industrial gloves but none is really
meant for these low temperatures.Friday and a balmy 28F, -2C in the shed meant I could brave the cold to re-position the D-ERF and other baffles. D-ERF is now better squared on at 27cm from the objective end of the tube. The largest baffle is now just inside the tube to stop down the 150mm f/8 objective to 120mm @ f/10. The sky promptly turned dark and cloudy to celebrate the moment after fleeting sunshine earlier in the day.
Sunday: It has risen to
26F, -3C with a roaring gale as I prepare the H-alpha solar telescope
for fine adjustment. I quickly checked the focus with just the D-ERF in
the system. The sharpest solar image seems to be at 27.5cm from the plywood
backplate. Whoops! I thought it was much shorter than that. It's lucky I
now have a good range of extenders! In the end the WO 60mm extension was the perfect length to house the front AOK-etalon adapter. I took a handheld snap at the Cemax 12mm and "processed" it in PhotoFiltre7.
Viewing straight through I had seen a large prominence in the form of a mu and another looking like a pair of opposing brackets. The fuzzy mess on the limb [right] was the mu. I seem to have captured some surface detail despite my best efforts.
When I attached the 1.25" star diagonal I needed a rather shallow extension. A 2" to 1.25" adapter, 22mm long would probably do it. See image at the top of the page. Bright sunshine soon turned to dense overcast before I could explore best tuning and focus. Hours of poring over astro sales websites produced nothing useful. I shall have to make my own on the lathe.
Or not. T2 fittings are not exactly cheap but will solve my optical, path length problems. While leaving me with a whole range of potential options. Order placed. Pictures when they arrive.
I was able to see several prominences quite clearly using a variety of eyepieces. Surface texture was visible in a ring with a blank center. A red blush lay off to one side of the sun's mage. Possibly misalignment of the D-ERF? My attempts at handheld 'snaps' today were no more successful than last time.
Further advice from an expert suggests my etalon is too far out. The straight-through, back focus REAR of the etalon adjustment band should be 200mm. I thought I was working from the front! So the rubber band width has to be added to the measured length. Unfortunately I cannot measure the true back focus without sunshine. None is forecast for the next week. The WO 60mm extender has serious clamping for the AOK etalon adapter. So I 'd like to retain this even if I really need a shorter fitting. Time to start counter-boring the plywood ring. I could fix another plywood ring on the back to maintain hole depth and stability. The sloping, security cutaway on the telescope side of the WO extender doesn't help stability in a parallel hole. Nor, probably, when a compression band fitting is used to hold it in place. I hope to turn a solid aluminium backplate when I have finalized the dimensions. It is premature to start now. Hence the plywood ring. Five minutes was enough to counter-bore the 2" central hole for the WO extension to sink 1cm into the surface of the plywood ring. The etalon band is now exactly 100cm from the ridge between the objective cell and dewshield. I removed the cell and measured the depth to the back of the objective to be sure.
Click on any image for an enlargement.
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