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Captain Magenta

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About Captain Magenta

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    SW Ireland & Middlesex

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  1. The secondary mirror and corrector plate are coated in SiO2, i.e. quartz. It’s pretty hard stuff! After removing the secondary baffle I used cotton swabs paintbrush and acetone to remove glue residues, even (especially) superglue disappears with that. Once the glue has finally dissolved, I treated it as if it was any other lens surface and cleaned again with acetone-cotton swabs and pure water. however if you’re not going to remove the secondary baffle, then I shouldn’t worry about cleaning the secondary. I only did it because my baffle was seriously off centre so I pulled it off and had
  2. The focus mechanism consists of a threaded Rod rigidly connected to a bulkhead which is bonded to the the back of the primary mirror, both of which are rigidly connected to the outer of two baffle-tubes. The knob turns a threaded nut also on that shaft but fixed to the rear of the ota. As you rotate the knob, the threaded Rod travels in or out through the nut at the knob, dragging the primary mirror arrangement up and down with it. It’s crude but it should work well. it may be that the attachment of the threaded rod at the bulkhead inside has worked loose, which would explain the behaviou
  3. I take it you don’t have a mount with encoders? If so you could use the encoder output as a theodolite to measure small arcs? I do that with my ayo2 and dsc. Or perhaps plate-solve the exact FL of one of your scopes and subsequently use the distance across the sensor between a pair of terrestrial features to derive angle from that?
  4. Have you seen Pulp Fiction? ... "Thread's dead, baby, Thread's dead..." ... actually i hope it isn't. I've been playing with MTFmapper and it is very good. I have a printout of one of the A3 test-chart versions and I'm awaiting the 80kph winds to die down before I can find a sufficiently convenient 50-odd metres target distance for my Skymax 180.
  5. I split it with my 12" last night. It was a little breezy and moving around from time to time. It was definitely there at 304x but to be absolutely sure I ramped up to 522x. Cheers, Magnus
  6. I set up the 12” OO-mirror SW-blue-tube newt this afternoon in spite of the bright Moon, as I haven’t used it for ages. A bit of a waste of big aperture but I’m a rebel. I’d earlier changed a setting on my Nexus DSC to display alt-az coordinates instead of equatorial and in the field trying to control my ax-eq6 it didn’t like it one bit. At the first opportunity after alignment it wanted to flip azimuth 180 degrees. I ended up doing alignment about 10 times before I realized what might be the problem. I flipped the setting back to equatorial display and all was good again. Must report it to Se
  7. ... just had brainwave (highly abberrated wavefront though) ... it's a parallel-sided pole, I'll measure its circumference tomorrow...
  8. Nice by proxy! The earthshine was very noticeable last night for me too, but it was all that was ... there was a small band of cloud-free sky just about where the Moon was, but that was it. M
  9. I'll try to address the precise distance-to-pole thing tomorrow. The FL of the scope as used for the photo, at 2799mm +/- 17mm, with this combination of camera and adapters, I am highly confident of. In fact I've done quite a bit of measurement of this, ending up with the following chart. I had an extra approx 40mm of back-focus from the "B" point in the chart below. A longish thread (Im the OP on it )about this can be seen here.
  10. OK raw image attached here... _S7A5565.CR2
  11. I find that a rocket blower gets rid of perhaps half the dust, the rest stays firmly in place. I've read of 3 extremely respected people in the industry recommending and using the fingertip method on their optics, and I do, or rather did, buy the arguments about it, before I read that there's significant quartz in house-dust. The story is that if a surface is quartz-coated, quartz being really quite hard, and you gently, I mean gently, rub your soft fingertips over the mirror or lens surface in the presence of water + detergent, you'll end up with a good result. My own direct convers
  12. I stepped away from this thread for a while and returned to find it covering 10 pages! This is going to be incredibly useful. I already have an FFT algorithm which I wrote a few years ago as a function for Excel for different purposes (analysis of accelerometer data for a rowing boat - see my sig/blog where there are some more details, not of the signal-processing which was inconclusive, but the acceleration data itself). I I may well be bale to bring this tool to bear on this. I do have a couple of questions though: - The straight edge? Should it be Black/White, or is any darke
  13. It's my understanding that most mirrors and lenses these days are, in addition to anti-reflection coatings, coated with a scratch-resistant layer on at least the surfaces that are exposed to the elements and likely to get contaminated and therefore cleaned and touched. I've tried to search the literature for what those coatings are actually made from, and it's surprisingly difficult to get any concrete information. The search results are mostly of opticians trying to sell you scratch-resistant coatings for your new specs. Even the remaining 5% of search returns say "we employ CaptainMagen
  14. Valentine’s Day present ... 100% increase in my filter count, adding to the Oiii I already have. Cheers, Magnus
  15. Carlo Rovelli’s Reality is Not What it Seems (or perhaps The Order of Time) is a superb mainly qualitative discussion of just this stuff. How a photon halfway from Andromeda is in Andromeda’s past but our future. How it’s possible indeed commonplace for any of us to time-travel forwards but not backwards. By far the best explanations of these mind-exploding things I’ve read, anyway. Magnus
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