Captain Scarlet

Just saw Mercury first time this year. 60x with the Kowa 88 spotting scope. Very definite 45% phase going on… Hopefully more to come later for First Light with my finished 8”: Magnus

Yes I have a number of things I still want to do. One of them is just what you say: to grind off the excessive diffraction-contributing overhang of the mirror-clips and replace them with the minimum necessary to stop the mirror from falling forward when inverted. Also the secondary is bigger than I want. 63mm, i.e. 31.5% CO. I’m strictly visual so I’ll be getting a 50mm secondary at some point. M

Bracknell not far from Wokingham, which is where @Stu used to live … he’d be a very good person to guide you as to local spots And welcome to SGL, Magnus

I went to the hardware shop today and got some hinges. @Roy Challen. A little drilling of a few extra holes later, my rings work as they should, no bungees in sight! A little black paint tomorrow and nobody would be any the wiser! Ready for First Light, whenever that may be…

Haha that was the other thing I thought I'd wait until someone else noticed before talking about it! You suggest it might be "ventilation hole for the fan on the cell to pull air from in front of the mirror". Well, yes it is, er, sort of, by default though. There are two explanations: 1. I'd designed the whole thing to the nth degree, worked out where I needed all the holes etc etc. I measured and measured and checked and checked before drilling all the small holes: spider-holder holes, mirror-cell attachment holes, finder-bracket holes, and the single pilot hole to act as a guide for my 80mm hole-cutter for the big focus-tube hole. I have to say, I drill very nice holes with great accuracy, working up from 1mm hand-held spotting-indentation, drilling then all the way up to the required size. Very careful. Finally I got my 80mm hole-cutter, run backwards of course for easier cutting without catching, lovely smooth and also a good job. Lovely lovely. 10 seconds later I realized that I'd used one of the spider-holes as my pilot hole, not the focus-hole pilot hole. ........................................... Oh God. Oh my God. You can imagine the stream and volume of swear-words as I strode around the house holding my head in my hands. How could I be so BLOODY STUPID! 2. In the design phase, I had given a lot of thought to the thermal management of closed Newtonian tubes, especially extremely well-insulated ones like this with its epoxy-carbonfibre skin and 5mm hardfoam inner liner. I had genuinely been mulling about creating a focsuer-sized ventilation hole near the primary mirror. But in the end I decided to "go conventional" to begin with , and decide later. This stupid mistake made my decision for me. Once I'd calmed down, I realized I could simply turn the tube back to front and start again. Which I did, being very careful second time to use the correct pilot hole! Hence the makeshift "hatch-cover". If you look carefully at the images, you'll see various random "unused" holes and bits of tape covering holes, the collateral damage of my idiocy. You also say "nice shiny tube". It is, of course, it's beautiful, but more to the point it's extremely stiff, more so than I was expecting. Exerting some serious force to the laser when in the focus tube, I could not get the spot to move. Very pleased and well worth the wait for Klaus Helmerich.

Mark d’you reckon it’s viable commercially? Looks as if it might be to me. I for one would definitely be a buyer. M

Haha I was wondering if anybody would notice that bodge! Well spotted. One of the unanticipated difficulties from the extra ota tube thickness. I’ll probably use the existing OO rings and add the required distance with some slightly longer hinges from the local hardware store … it’s all pretty crudely put together as it is.

Thank you. The view is much of the reason we moved here. The other is the darkness. By coincidence after a long dry spell (in sunset terms) this vista presented itself just this evening...

Over the last few weeks I've been gradually morphing an Orion Optics VX8 1/10 from the sorry state of affairs it was when I bought it, to a state of loveliness, in both form and function. To look at, the original VX8 scope was fine: newish, clean, no scuffs etc. It was only on close inspection that some serious problems became apparent, to the extent that it was essentially uncollimatable, and therefore horrid to look through. These problems were no fault of the SGL member who sold it to me, though it may well have been some of the reason he sold it. The as-sold OO VX8 has design flaws and in the case of this copy, production flaws too. I've tried to fix all these. I've transformed it into what it should be, and some. It's now a beauty to look at and, I hope, to look through. Though I haven't yet had a chance aside from doing the collimation. But I have checked that my design work worked: I reached focus just where I hoped it would be, 70mm from the outside of the tube. Phew! The main problems I fixed were: - The centre-spot on the primary was 3mm (!!) from the true centre of the mirror. It was this that made it virtually impossible to collimate or get a decent view. I removed the old spot and installed a new one, properly centred. Now the 1/10-wave spec can do its thing. - A new Klaus Helmerichs carbon tube. The original VX8 tube is Aluminium and thin, therefore not rigid. Any significant eyepiece-train load would cause "droop" and collimation-shift. The new tube is extremely stiff, I can't shift collimation with even a hard pull on an eyepiece. - The VX8 has end-rings to try to keep the tube round at each end. To keep them stiff, these rings wrap over across and into the open end of the tube, leaving a resulting clear aperture at the front of the tube of exactly 200mm, i.e. the same as the primary mirror 871mm away. This means that only the precisely on-axis spot receives the full 200mm. Anything off-axis gets vignetted by the end-ring. The new tube has no such "wrap-over". - The OO cell is actually a lovely mirror cell, and I would certainly buy one new. But in the factory during assembly all its moving parts and more besides get slathered in gobs of silicone glue. Why on earth? The whole point of the cell is exactly its moving parts. Anyway, I removed all that nasty stuff, plus the sticky-tape untidily wrapped around the edge of the primary, so the cell can now support the mirror in the way it's designed to. The first image below shows everything neatly arranged, ready for assembly. Easy final step, right? Wrong. The extra 6mm tube-thickness presented me with a good few difficulties, some anticipated but some not. Luckily I did find ways around the unanticipated ones. Neat and Tidy and ready for assembly: The extra tube thickness meant that the spider wasn't quite wide enough. Luckily I had enough M4 nuts lying around that I could insert between the boss and the spider-arms, giving some crucial extra width: The lovely rear cell: Some pictures of general loveliness: And finally, it joins its bigger sibling (a 300mm OO 1/10 mirror with Helmerichs tube): Thanks for drooling, Magnus

Mercury! Thanks for the reminder. It's higher now for us at 51 degrees N than it has been for some time, until end April. M

West Cork yes indeed! Setting up only the refractor on the ayo just outside the house took ages because I would stop and stand and gawp between trips. Magnus

Tonight satisfying and frustrating at the same time. Satisfying because it was a lovely clear night with the Moon not due up until 0055. Satisfying because seeing was the best I think I've ever experienced (star-testing Polaris showed crisp perfectly stable rings both sides of focus at max mag for the scope I had: 217x with 0.48mm EP). Satisfying because it was the second darkest night I have ever measured here, in 5 years. 21.97 on my SQM-L. It was fascinating to see it get darker as countryside lights went out, and then get "brighter" as Luna started to approach Moonrise. Satisfying because the transparency was superb: the MacGillicuddy Reeks 60km distant were very sharply defined before sunset, always a good indicator. Some supposedly clear evenings you can't see them at all. Frustrating because, lovely session though it was, I HAD THE WRONG SCOPE OUT! I'd put out my 105mm LZOS for a very short wide-field session as I had early errands next day. It turned into a longer session, damn the early start, I wasn't going to miss skies like this even with the wrong scope. I dearly wish I'd got my 12" out. The whole session worthy of a separate report over the next day or so I think, but I had far and away the cleanest best view of Epsilon Lyrae, the Double Double, I've ever had bar none. By no means the most difficult target I know, but still a good indicator. Cheers, Magnus

OK I’m TRYING to get on with this, but I have some difficulties… … HE thinks he’s helping

Does Mrs Stu know you have this much time on your hands? 😁 M

I plucked up the courage actually to perform the centre-spot placement today. I initially intended to use the template to mark a marker-pen spot, and with tweezers place the centre-spot over it. But I found my hand wasn't perfectly still enough to be certain of getting the initial spot in the right place. So I adopted a different strategy. I taped the triangular spot to my template in just the right place using a piece of low-tack masking tape. I removed the adhesive backing from the centre-spot. I placed two strips of multiple-layer flocking paper, one on each side of it to give clearance, to ensure that when I laid the whole thing onto the mirror, it wouldn't stick until I was happy with the positioning and pressed it down. It worked first time. The spot I also made from black flocking paper, in my never-ending quest to remove any source of bright scattered light from my tubes (i.e. from a white spot). Success! Whereas before the spot was fully 3mm from the true centre of the mirror, almost on the paper of the donut, now I've measured it to be 0.2mm from the centre. I reckon I'll not get it better than that. Cheers, Magnus. Pics below preparing the press-on template: Laid in place and ready to press down: Finished result (central dot marks the true mirror centre in the last pic):

First Light in Ireland for my LZOS 105, I’ve been dying to try it for years actually with my Nagler 31 for 21x nearly 4 degs FoV in dark (-ish given Luna) skies. Lovely quick tour of a few favourites including double cluster, Alnilam S, Pleiades, Polaris A/B and half-split the double-double with the Delos 6. 4 Trapezium stars were detectable with the N31 too which surprised me. Observing chair certainly helped there. As mentioned in the Lunar observing thread X and V were seen, and a random occultation, around 2225, it just snuffed out, I think it was that well-known star TYC 1903-0472-1 😂

Me too with all three aforementioned, first time noting them also. First Irish Light for my LZOS 105. Magnus

Those who noticed my recent “Deconstructing, Fixing and Upgrading a used OO VX8” thread may recall that one of the problems I identified with the scope, with the mirror itself, was that the centre-spot “donut” was manifestly not in the centre. This makes the scope essentially uncollimatable, or guaranteed to mis-collimate. The method I used to establish this was to take a DSLR photograph of the mirror, face-on, with a reasonably long focal-length camera lens and the picture centred around the centre of the mirror. In Photoshop I then chose three arbitrary roughly-equally-spaced points around the edge and noted their pixel-coordinates. I used a formula to determine from those coordinates, the pixel-coordinates of the true centre of the mirror. I’ve since worked out a less involved way of checking this, which can be used both to check the centred-ness of a spot already in place, AND to place a new spot centrally when the time comes. A common suggestion is to trace a circle on a piece of paper or card, fold it over a couple of times, and where the folds meet, there is your centre. That’s fine, but my new method lends itself better to using graph paper, with no need to try to cut accurate circles or curves. It turns out that a 3-4-5 triangle has a couple of really nice properties: one, it’s a right-angled triangle so its corners can be trivially marked on right-angled graph paper. And second, the centre of the circle that passes through the three points of the triangle has nice round-number coordinates too. So a triangle that has the coordinates (0,0), (0,3) & (4,0) will have the centre of the circle at (2.0,1.5). All extremely easy to scale up, no nasty pi-related fractions of millimetres to try to judge, rather easy to mark directly onto graph-paper and cut out, and possible to check and re-attach a centre-ring without removing the mirror from its clips, as the 3-4-5 will fit inside them, as shown. In case anyone likes this and plans to use it, I’ve added a little table below with the triangle-and-centre coordinates of some common mirror-diameters, plus a picture of my own in action. If you look closely at the hole I made in the centre, you can see just how far out my own spot is! Cheers, Magnus

Happy Birthday. We of course will need to see any astro-related presents! Magnus

When it does come time to clean it though, bear in mind that what’s on the mirror is no ordinary dust, it’s very fine _sand_ and needs extreme care to clean it without leaving scratches

At the very worst I'm 2.5 hours drive away in Baltimore, I'll get there one way or another! My neighbour will know plenty of people who live much closer so I'm sure it won't come to the full drive.

Thanks for the reminder. I've just made an enquiry. Hopefully they'll have space, and hopefully I'll be able to meet some other Ireland-based astronomers. My big dob might even be ready by then! Magnus

Wow what a read! Well worth the mirror-hassle I hope. Did the B&B landlord show any interest to have a look through? Magnus

Yes this is a worry for me too. The residues of silicone especially on the sides add friction when dry and might reduce friction when wet, making misjudging grasping it all the easier. Will have to be extremely careful.

I did put it the top half back together again before putting it into its travel-capsule, and it fits in fine with enough clearance to allow it to all work as it should. I'll demonstrate in a few days when I resume the build. I do plan on a couple of modifications though. I'll grind off the "hook-over" bits of the restraining clips: they're far too big for their job and will introduce quite large needless diffraction artifacts. I'll replace them with a much thinner (from the point of view of the light-path) arrangement, perhaps such as Obsession suggest for their big dobs. And if I'm only ever going to use it on an alt-az mount, I might fashion a sling between a pair of those side-posts to spread the load more evenly. It won't make too much difference on a mirror as small as this but everything counts and it's all practise for my impending 20" dob build for which such an arrangement is truly necessary. My calculations might be wrong but on an initial lookup Aluminium's expansion coefficient (dL/L = 23e-6 per K) suggests that a, say, 160mm length will contract by 1/270th of a millimeter per degree change in temperature. Or for 10 degrees change, that's 1/27th of a mm. I can't believe that's enough to noticeably pinch from the standard suggested "paper-thin" gap unless the nylon side-grubs have already been tightened onto the mirror? (Which I used to do myself before someone asked me innocently why all my stars were triangular ) Cheers, Magnus