Captain Scarlet

I think it may even have been mid last week I had my first clear sky in ages. Unexpected at the time, so without bothering of a telescope I put on a huge coat took a chair into the field behind my house and just soaked in the stars for a couple of hours. SW Ireland so not unlike N Wales very dark, but the stars so bright and so many.

There’s been some talk on SGL lately about messier and how his list came to be. There was discussion about M1 and how it’s not the easiest of his list. So with unexpected clear sky tonight I set myself the goal of trying to find it. I’d only set up my 6” Intes Mak, not the 12”, so I wasn’t too hopeful. But I found it very quickly, rather a bright large smudge with my Pan 24, sitting on the left edge of an upside-down kite, as seen through the eyepiece. No real detail though, but I expect that to change when I bring my 12” to bear. Chuffed, it’s another “tick” for me. M

I think the strength of the diff spikes depend on the lengths of straight edges, thickness doesn’t really come into it. The thickness will increase obstructed area of course and thereby reduce contrast, but the spikes will be unaffected. a single vane obviously has 2 edges and will throw out 2 spikes from a star in two directions perpendicular to the edges M

Search on that popular auction site for “bionculars” i.e. misspelt. I did this by accident once and picked up a very expensive pair (Leica) for around 50% of their proper value. I couldn’t understand why nobody else had bid, then it dawned! You might be lucky. M

I too have an az-eq6 and wifi dongle. I get the whole thing up and running including alignment using the synscan pro app, then I launch skysafari pro and can control from that. though I use an iPhone. Magnus

Looking at the orientations of the coma (long axis of coma pointing towards above the top-centre of the image) it looks as if there will be a coma-free point somewhat above the top of the image. That suggests to me as well, miscollimation. Magnus

Funny I have a list of Southern Hemisphere objects I’d really like to see, I’d never considered the other way around! Thinking about it now: Andromeda an actual galaxy visible naked eye from a dark enough location. And such iconic shapes as Ursa Major and Minor, Polaris as you say, never visible from the South. I too hanker after 47 Tuc and the Magellanic Clouds! And Crux. Cheers, Magnus

Superb. Would be interesting to see if anyone else gets that “on-off” of the nebulosity when looking at and away from the Trapezium

1st Jan 2021 - Skymax 180 on Ayo2. Near-full Moon. The forecast was good for New Year’s Day’s night, although a 98% Moon was likely to dictate things. The forecast for the following week+ was very good, so I thought I’d get into the groove in spite of Her, and give my Skymax’s new Feathertouch focuser its first outing. It was also a first opportunity to use my new encoder-unit for the Ayo2 with my Nexus DSC. And another first: my very first use of a Bahtinov Mask, brand new in packet despite being amongst the very first batch of stuff I thought I needed when starting out back in 2017. It really works! And such big bright spikes! (such big teeth Mr Wolf!) The Nexus-DSC/Ayo2 was a joy to use, and it dawned on me (sorry I’ve headed off on a tangent…) that the “go-to” “push-to” etc is all about, and only about, initially acquiring the target. Once you’ve got it, whether you’re tracking or nudging, it’s thereafter easy (I speak as a pure observer). I had been afraid, skeptical even, about “nudging” to keep something in view, but having done just that now with this manual mount, I’ve lost that fear and as you more experienced observers have written many times, it’s not an obstacle to worthwhile observing at all. Also, the Nexus DSC’s pre-sets allow for multiple, up to 6 I think, mount settings, with an instant switch between separate direction-arrow-rules and encoder resolutions. Anyway, sorry, back onto track. I attempted the Trapezium with the Skymax, namely the E and F stars, but I had no luck no matter how hard I stared. I had still yet to see them at all. So I simply used the Nexus’ “Tour” facility to scroll through any interesting objects within 10 degrees. I enjoyed many decent doubles in Orion, though I should have noted them, as some I would like to revisit. I need to start note-taking. Even sketching actually, given what's to come (read below). I spent some time on the Moon too, which seemed stable enough even at more than 300x, so perhaps the E & F stars need less ambient glare. 3rd Jan 2021 - 12” OO Newt on AZ-EQ6. Trapezium. 2nd Jan was cloudy in the end, but 3rd was looking good. I did 2 sessions divided by dinner, and the night was all about Trapezium E & F stars. This time I had the big 12” Skywatcher metal-tube newt on my AZ-EQ6 and Planet. The Moon wasn’t due up until nearly 10pm so I had a bit of dark-time to play with. Before dinner, a quick look at Rigel and Alnitak showed 2 kaleidoscopes. Never mind Sirius. So the seeing was terrible, and this manifested in again a complete failure to spot the Trapezium E & F. Inside for dinner. Coming back out, I spotted them immediately! Weh-heh! There they were! My first time! The seeing was much better less bad. E and F were by no means pristine, and they came and went, but they were definitely there, E much easier than F, and not unlike a tiny version of Ludwig’s Star offset between Mizar and Alcor. My current 12” “rig” comprises an OO mirror which replaced my SW mirror, but with increased FL by 90mm. Plus a Paracorr 2 which further requires extra out-focus. The combination of the two resulted in a huge cantilever sticking out the side of the tube (I have a re-delineated Carbon tube on the way) and it occurred to me that this might “droop”, given the crudeness of the steel tube, thereby throwing collimation off. Up to then I’d been collimating with the laser right in the focuser, then sticking the whole stack back in. I decided to collimate this time with the laser at the end of the stack, and sure enough it was quite different from before! The re-collimation made a difference: the E and F were significantly cleaner afterwards. However a quick look at Mars and the Moon (up by now) showed the seeing was still not good. In these rather dark skies, 21.4 before Moon tonight, and with 12 inches of aperture, M42’s nebulosity around the Trapezium was incredible. Not just veiled versus not-veiled, but smooth contoured varying strands, like cream in coffee, and through the gaps deep black. Wonderful. What it must be like through a truly big dob! I did notice something weird though. If, using 100x or 180x magnification I looked away a bit to the East of the 4 main stars, I could see all this amazing nebulosity and the contrasts quite plainly. But the moment I moved my eye to look directly at the Trapezium, all the black would suddenly “fill in” to become the same lighter shade as the nebulosity. In other words all my subtle contrast would simply disappear, like a switch. On or off just by looking at or away. I spent most of the session on the Trapezium. I did briefly also try for the Flame Nebula, and noticed nothing. I managed to split Alnitak though, which was nice. 5th Jan 2021 - 12” again. Mag 21.51. Trapezium Again. I set up late afternoon, a sparkling night in prospect, and headed inside to dinner. When I came back out, so had the clouds! There was a clear patch towards Polaris and the Great Bear, so hoping the cover might somehow disappear, I collimated (barlowed-laser, the paracorr acting as barlow, and refined using my new technique and diy tool) and aligned on Polaris and Dubhe. By now the bright patch had increased in size and I could see an end to the cloud-band in the direction-of-weather, NE. Superb, it looked as if it might be clear after all. I quickly took in M51, lower down than I had remembered, and in the only nearby bit of light-pollution so I quickly moved on to M81 & 82, both nice, but not my intended for tonight. That was, for a change, the Trapezium! And maybe, conditions permitting, the Flame and the Horsehead. The sky had almost completely cleared and it was beautifully clear. Seeing seemed not bad too, with Sirius actually stable and round, in fact the best I’ve ever seen it; though try as I might I could not find the Pup. The star was above the one house in that direction (think heat plume) and having checked where the Pup ought to be, it was going to be directly beneath a diffraction spike and I wasn’t about to rotate the scope in its rings. I tried for the Pup several times during the night, but no joy. Whereas my main target for the night, once again the Trapezium, was MUCH clearer than two nights ago. Before, the E and F stars were definitely there, but hazy and coming and going; tonight they were all pinpoint and stable at both 183x and 305x with my Delos 10 and 6mm. I spent ages admiring not just the stars but the sheer variable milkiness of the surrounding nebulosity. Furthermore, in my optimism and excitement, I thought why not try for the G or H? I did spend quite a while staring at where I knew G to be, but not a hint. If the E and F at mag 10 are just about discernible, mag 14 would’ve been all but impossible in all that nebulosity and close to the mag 5 and 6 C and D stars. I guess it’ll take a perfect night and more aperture and magnification. Another problem was that although seeing wasn’t bad, there was a bit of wind and every time it got stable enough, another little gust would come through and shake things up a bit. Big 12” tube on Alt-Az mount. I’ve read somewhere that if you can see the Flame Nebula, then the “Horsehead is ON!”. Well I could see the Flame, quite distinctly, in the DeLite 18.2 at 100x, so I instructed my Nexus to take me to Barnard 33 (Horsehead). Using averted imagination I could perhaps think there might have been a slightly darker shaped patch where I was looking, but I don’t think so. Another day. Finally, as I was slewing around the supposed-Horsehead area looking for it, suddenly an exquisite collection of stars streamed across and I just had to stop and go back. Not just a nice collection, but captivating. It also occurred to me a moment later that it was the very same collection of stars that that evil man @Stu used 3-4 years ago to infect me with Refractoritis by showing the same to me through his Tak. It was, of course, Sigma Orionis, and the view of it this night was literally arresting. So sweet and pinpoint. At around midnight at -3C and a NE breeze, my feet eventually drove me inside. Sorry I’ve gone on and on again but I have re-lived the experiences just recounting all this. Cheers, Magnus

It sounds from your description it was definitely Polaris and its little companion. I always use Polaris as an alignment star, and use that tiny blue dot to ascertain that it’s Polaris I am actually looking at through the main scope, as so many more stars appear that it would otherwise not be obvious. 19 arc seconds is the split I think, close enough to be sure but almost never to close to not see. Lovely sight IMO. Position angle would depend on what time and what diagonal/mirror config you had I think. Incidentally I tried for it once side-by-side with a 200 newt and a Leica 62mm spotting scope. It was very obvious through the 200p, but I couldn’t see it through the 62mm. Cheers Magnus

That reminded me that I thought I'd read in Suiter that Maks necessarily have some detectable SA inherent in the design. I looked it up: In Edition 2, Sections 11.1.1 & 11.1.2 are the requisite bits. He seems also to imply that it doesn't matter much, they can still be very good. Magnus

... went out again after dinner and the seeing was considerably less bad. Bagged them both immediately. The E much clearer to me than the F but no doubt about both. Spent quite a while on them and moved briefly on to Mars and the moon both of which confirmed the seeing was still far from good. Very pleased though.

Well certainly not for me yet tonight, despite the 12”. Seeing is appalling, Rigel and alnitak like kaleidoscopes. View much worse than with Mak the other night. Oh well, decent forecast for next 4-5 nights so I’ll persevere...

I’m going to cheat tonight and deploy the 12” newt...

I had a go last night with my Skymax 180 and maybe maybe maybe imagined the E for a fleeting moment. At around 150x. Personally I won’t take it as a “tick” (still haven’t bagged them) but I’ll take the tease and persevere. A week of clear nights forecast so I should get plenty of chances. M

Holy thread resurrection Batman. Well not so old I guess. I myself ordered one of Klaus’ tubes a month or so ago, and eagerly await delivery. I replaced the mirror on my SW blue-steel-tube newt for an OO 1/10 wave mirror. The FL is slightly longer, hence ordering one of Klaus’ tubes. The carbon over the steel with save me around 5kg too! As soon as I get it and have had a chance to use it I’ll add an update here... Cheers, Magnus

I measured the whole-system EFL - i.e. took photos of a star-field - at two widely-spaced values of back-focus. I have an 80mm extension tube. When I ran the numbers of resulting EFLs with my existing values and equations, I couldn't get them consistent with properly-measured mirror-separations or back-focus values. One or other value of back-focus, but not both. Somehow I needed an extra degree of freedom. I suddenly realized that one measurement I had made was a weak point: that of the FL of the primary. It was the shakiest measurement of all those I'd made, furthermore I had done it "naked", i.e. without the corrector plate in front of it. So I re-ran my maths ignoring the measured FL of the primary as well and solved for two unknowns: the FLs of both the primary and the secondary. All my other measurements I was happy with, had small errors and those fed through into the small errors I have for the FLs and the system EFL. It's still not perfect, the effect of the corrector plate is not mathematically accounted for. Rather I've just let it become a "property of the system" inherent/embedded in the implied results, but my back-focus <=> EFL and mirror-separation <=> EFL all now give correct enough results over the focus-range. Cheers, Magnus PS I had the scope out last night, I really do like it...

Yes it’s rather disingenuous to claim the central obstruction at 23% ... skywatcher themselves make that claim!

It's quite amazing John, you're able to find a use for a handle anywhere! 😉 M

How did you do this? Are you looking at a point source and simply drawing what you can "see", i.e. the light-pattern on your retina/s? I've often wondered about my own distinctive point-source-retinal-patterns and whether anything useful can come out of inspecting them. I can easily draw them and even see their relative sizes. My spherical correction is around 4 in one eye, with bad and multi-axis astigmatism, and 1.25-1.5 in the other without much astigmatism.

Have your fingers also gone black by this stage? 😉

I should have added those other details that have changed from the original post too, thanks for reminding me. In fact my new more-accurate method caused me to change both the FL of the primary mirror as well as that of the secondary. I've added these details to my "recap" post just above. Basically, I've added the following: "Primary FL: 463.3mm +/- 1.6mm; Secondary FL: 115.7mm +/- 0.7mm" Cheers, Magnus

Yes I second that, a superb book M

To round this off, now that I’ve made all the measurements necessary to eliminate a key (and it turned out, wrong) assumption I made in my original post. To recap: in my original post I didn’t have the wherewithal to actually measure the focal length of the secondary mirror. So I assumed the EFL of the scope was as advertised, 2700mm, with the supplied accessories and associated back-focus value, and from that I "backed-out" the implied FL of the secondary. Eventually I was able to make measurements to accurately establish the true value of the secondary's focal length. I didn’t measure the mirror’s FL directly, that’s still too difficult, but I did measure the whole system’s focal length very accurately, by photographing star-fields, and was thereby able to back out the secondary's true FL. The upshot is that with the supplied accessories – a 52mm-long visual back and a 2” diagonal – the focal length of the system is 2883mm (+/- 16mm). Or F/16 assuming 180mm aperture. This certainly helps explain why I was seeing smaller fields-of-view than I was expecting, which started the whole process off for me. In other words, as supplied this scope is NOT the 2700mm specified, it’s nearly 200mm longer. Also in the process I've been able to home in far more accuyrately on the FL of not just the secondary, but the primary too. They are: Primary FL: 463.3mm +/- 1.6mm; Secondary FL: 115.7mm +/- 0.7mm The back focus required to achieve the 2700mm FL is 118mm, which may well be what the Visual Back + Diagonal configuration was when it was originally released with a 1.25” back. I have also reformulated the chart of EFL-vs-BF to replace the one in the original post. Cheers, Magnus

Hi Steve ... how’s the scope been? I hope good. I’m toying with getting a Taurus myself. Cheers, Magnus