Captain Scarlet

Thanks for the reminder! I'd have completely forgotten. My forecast says I may just about have a window in the weather around 5pm tomorrow, which for my location will be the optimum time. Magnus

You could also use those hole-cutters for wood without a drill, simply turn them by hand

Out tonight briefly as it was unexpectedly clear after a rainy afternoon and evening. I only took my 15x56 bins, it was too windy for anything more elaborate. As my previous post suggests, I first looked at the Pleiades and of course Ally’s Braid. M81/82 were found quite easily, but M101 and M51 eluded me, they were still too low over the main light dome over Skibbereen, with some haze still around. M31/32/110 were easy (M31 naked eye too) and while up close to zenith I found Kemble’s Cascade. M33 was quite evident, perhaps even a bit of structure, so on that basis I returned to M101 and eventually _just about_ found it. I thought about going for M1 Crab, which I have seen through these bins from this spot before, but for stability I’d’ve had to sit in the garden chair I keep there, and that was still slimy wet, so no. Meissa was lovely (I call it the “Luger” asterism), as was Mintaka’s S and of course M42. Impatient now for a proper scope session before Luna reappears. Magnus

I believe it does, it’s called “Ally’s Braid”, as in “Alcyone’s long hair”. Personally I call it “B2 Bomber” as that’s what it reminded me of when i first found it and didn’t realize it had a name. It’s one of the first things I go for when I’m out with binoculars ( like tonight!). Magnus

I believe @PeterW has actually looked through a pair of these…

I saw about 15 in 45 minutes last night, two very bright with visible trails. Magnus

A brisk and freezing north-easterly meant no scope but I did dress up to spend 45 minutes trying to see some Geminids. Two really big long ones, one the second I stepped outside, and perhaps 12-15 more smaller ones. The best display I’ve ever seen.

Reasonably good DIY-wise. Centroid algorithms … can they cope with Newtonian coma? I’d be using pictures taken with no CC, of course. And where would I find one? Either the code or an implementation. Although I have a Raspberry Pi, a gift from someone who evidently wanted to waste a lot of my time (😈) I have not yet even got the bits out of the boxes … I haven’t dared.

A quick question Mark … what is the mostly-hidden blue structure supporting your tube in the middle picture? An orange-crate cut into a V or curve? I might need to emulate it for similar purposes… M

Thanks for the replies people. The small sensor size for a given price level for these cameras seems to be a deal-breaker for me. Even using a full-frame sensor a standard error (say 5 pixels) in estimating the exact centre of a star off an image translates into a focal length uncertainty of the order of 6mm for my 1800mm FL scope. A smaller sensor and bigger pixels will only amplify this. I might see if I can borrow somebody's mirrorless camera... Thanks, Magnus

6.5mm would certainly work, probably anything up to 15mm.

Unfortunately that would defeat my purpose, which is to measure the distance on the sensor between two known stars at prime focus so I can exactly calculate the focal length of the scope.

I'm not looking for a DSLR, I'm looking for a (perhaps old) dedicated astro camera to screw or mount directly on to a focuser flange. The brand name ZWO or QHY occur to me?

Ideally budget will be much less than the cost of a mirrorless DSLR. I already have a 6D and a 7Dmk2, so I wouldn't get any extra use from something like that. I'm hoping something inexpensive and perhaps a generation or two old might fit the bill and be cheap too.

I’m not an imager, nor can I see myself becoming a proper one. I’m too interested in Visual. However, I have been known to dabble especially for occasional wide-field MW style pictures, using my Canon 6D. But for design purposes I do occasionally like to know and/or measure the exact focal lengths of my scopes, particularly Newtonians of which I’ve built two recently. I find that the >=44mm out-focus requirement for a DSLR is too much for my visual-only scopes. So, my question: does there exist an inexpensive, say crop-frame sized, astro camera with a flange-to-focus distance of the order 15-20mm or less? It only needs to be good enough to capture focussed stars. Thanks, Magnus

Meade Rainforest Pro get very good reviews. A friend of mine has them and they are very nice to look through. Magnus

👍🏼 Yes my thoughts too about obsessiveness with autocollimators and other techniques relying on that spot. Both my OO 1/10 wave mirrors were originally wrongly spotted, one grossly so. As for the paraboloid not being symmetric, I think a grinding process more or less guarantees it must be symmetric, as accurately centering the position of a blank is easy. If it weren’t I think the mirror itself would be unusably bad in all sorts of other ways.

Maybe take the opportunity to check the centredness of the spot while it’s out? M

After First Light late afternoon/early evening in dark conditions, I went out later into the bright moonlight to resume. Tube sparkling in frost but optics seemingly clear. I couldn’t understand why when aligning on Capella I couldn’t get focus AT ALL, and Capella seemed much redder than it should. 🙄 stupid me. I’d pointed to Mars, which looked quite good high up at 141x. I went to Pleiades with my Nagler 31 to reassure myself that coma correctors actually work … they do! What a difference. I also noticed that with the secondary now so close to the open end, any local bright light source, particularly at right angles to the scope, really impinges. Need to fashion a dew shield. I looked briefly at Luna at 183x and noticed Lambda Cancri just off the Southern limb. I split Rigel but it was a bit wobbly and finished off with Sigma Orionis again, this time getting the C star but nothing really pin-sharp. Brrrr, Magnus

Indeed it is 😁. All that’s left Skywatcher-wise are the spider and the rings. They must be quaking in their boots, but they’re both fine so safe for now.

I’ve spent the last few days completely dismantling and re-building my Orion-Helmerichs 12”, ridding myself of the old Skywatcher 300p main cell and installing a brand new Orion Optics cell (about which a new thread will appear shortly, avec pics). Late afternoon and evening until just now was First Light for the new set-up. Focus was achieved - phew! My new holes were in the right place. Having just come in to the warm to prepare supper etc, my fingers now really hurt, it’s about -4 outside. But it was a really good short session, I did more or less what @Stu did the other day, took in all the available planets, plus Almach for some extra colour. Mars was too low really, but there was detail on view. Jupiter came and went with localized seeing, now mushy and now sharp. Saturn stole the show, Cassini Division easily seen plus Titan Rhea and Dione and possibly momentary glimpses of Enceladus but I’m not sure. Uranus was obviously a blue disc and Neptune a hint of greenish and just about discernible as a disc. Fingers bloody freezing, dinner now and perhaps another session tonight on the Moon. Very pleased with rejuvenated scope Cheers Magnus

Re apparent SA. I’ve had a particular phenomenon in the past, on two supposedly extremely well-corrected scopes, one a 105mm LZOS refractor, and the other a 1/10 wave Orion Optics Newt (with 1/10 secondary). It went as follows, on different occasions for each scope. One night, even after plenty of cool-down (hours) the scope showed terrible SA, untidy and spiky one side, crisp and sharp the other. Thinks to oneself “sell this piece of rubbish”. Then the next night, perfection (relief)! This has happened as I say to each of those two scopes. The difference between those pairs of successive nights was that the first night saw continuous and fairly rapid falls in temperature throughout the session, whereas the following-day “good nights” were stable of temperature. The upshot being of course that on the variable-temperature nights the scope’s temperature was never catching up, always distorted therefore showing poor correction. It was fascinating actually. Magnus

I can see an easy solution. Flock the chimney tube! Not the way flock tape normally likes to bend but I’m sure it can be persuaded! 😁 Magnus

Great topic Mark. It would be really good if someone who knows their stuff on these lines might monitor this thread and impart wisdom. I’ll certainly post up some of mine. My one main thought for star-tests for fast Newtonians for collimation purposes, is that one must not try to collimate away the offset in the doughnut to achieve perfect symmetry. That way lies guaranteed miscollimation. M

At Easter when the Milky Way is away from zenith I generally can measure 22.0 on a good night. In summer, 21.5 ish. A definite factor when agreeing to move out here 🙂 The only drawback is this thing called Irish Weather. We get everything the N Atlantic can offer. But on the good nights … my God. M