Captain Scarlet

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

5 minutes ago, John said:

Your report has inspired me to get my 12 inch dob out tonight .

Surprise clear sky here without a moon. E & F Trapezium and a lot of other stuff looking lovely

 

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

1^st 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.

3^rd Jan 2021 - 12” OO Newt on AZ-EQ6. Trapezium.

2^nd Jan was cloudy in the end, but 3^rd 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.

5^th 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

9 hours ago, Nik271 said:

 As I was focusing in and out it seemed that inside focus and outside focus diffraction patterns looked slightly different, I don't know if this is normal for Maks or just my scope. 

Nikolay

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

1 hour ago, alex_stars said:

Hi Magnus,

I see you have revised your primary FL (F1) also down to 463.3 from the initial 472 mm. When I run my estimates with this F1, I get a secondary FL (F2) of 114.6+/-0.7mm, so we agree within error bars. 😀. May I ask what caused the revision of the primary FL?

Clear skies,

Alex

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!

1 hour ago, johninderby said:

I’m waiting for eBay to publish guidelines which may help to get a handle on the situation. 🙏🏼

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

M

4 hours ago, vlaiv said:

... I examined PSF of star or distant light and this is what it looks like:

Single star is smeared into three images - connected but having distinct points of light.

Moon for example gives tree images in that same order - well two top images overlapping as distance is not that great and bright patch between all three prominent images.

I did try to view at high power in order to reduce astigmatism with small exit pupil and I have the feeling that things did improve somewhat - but I could never achieve sharpness and clarity of my left eye, regardless of focus position and pupil size.

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.

57 minutes ago, globular said:

... After each session the "this is cold" feeling lasts less and less and I no longer get that feeling at all any more. ...

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

8 minutes ago, Moonshed said:

I also noticed earlier that the sky was clear and stars were on display! Unfortunately however I have had glass or two of  Christmas wine and there is no way on earth I am going anywhere near my ‘scope until I can pass the astronomers’ sobriety test. For those of you who have never heard of it, because I have only just made it up, the test is to say out loud three times very quickly “Critically check crucial collimation carefully”. I can’t even say it sober!

That’s the first test. If you pass, the second test is to actually try to do it 🙃

@John and others have pointed out that planets often look good when there’s a bright moon up. Perhaps try for Uranus/Neptune and maybe their moons too?

1 hour ago, Cosmic Geoff said:

While doing some solar observing just now, it occurred to me that unless your mirror is smashed into tiny bits like an auto windscreen, you should be able to use the biggest piece to determine the focal length.  Set it up so that it focuses an image of the Sun back onto a piece of white card, and measure the mirror-to-image distance.  This will give you the focal length with a reasonable degree of accuracy.

Armed with the diameter and focal length, you can then get quotes for a mirror from amateur telescope makers and other optical specialists. Once you have an agreement in principle, you can give the maker the bits to play with, so that he can confirm the focal length and figure (spherical or ???).

Given that a MN 190, smaller than your scope, costs around £1000, this approach may prove cost-effective.

an alternative method would be to stick the largest piece onto a block of, say, wood, so that the mirrored surface is more or less vertical. Also make another flat vertical surface, into which you have created a small hole, and attach a bright light just behind that hole. A headtorch taped to the back of the board would do. Then arrange the two vertical surfaces (the mirror and the screen with a brightpinhole light-source) on a countertop, facing each other. The light-source will reflect back off the mirror and when they are at just the mirror's spherical-radius apart, the reflected dot will be at its smallest. The focal length of the mirror is half the sphere's radius. I have done this myself.

On a separate note, I had a mirror made for me recently by Orion Optics. Before it was ready I asked them precisely what focal length the mirror would come out, as their website wasn't totally clear on that point. They replied "They come out about 1590mm =/- 10mm". So I would imagine the matching of corrector-plate and mirror may well be Meade grading their measured-after-the-event corrector-plates and mirrors, and matching pairs thereof.

Cheers, Magnus

4 hours ago, niallk said:

I always had an interest when younger,  then I came out of a pub in the darkest skies of West Cork, and was just awe struck by the sky as I stumbled back to our accommodation after a feed of pints.

I too had my adult astronomy epiphany stumbling out of a pub in West Cork about 6 years ago. Having been used to SE England LP for most of my adult life, the blaze of stars against a sable backdrop that greeted me as I left Bushe’s in Baltimore blew my mind.