Captain Scarlet

The Leopard is an F3 Savannah, 6 years old, one of a pair of sisters who together with a boy Bengal, rule our household with an iron paw

or here http://klaushelmi.de/en/ , which where the TS ones may well be sourced...

(I'm planning to order a custom tube from here for my 200p, slightly longer than normal to allow my secondary to get fully illuminatedm which it isn't at the moment).

M

I finally got around to printing up and laminating a set of "scope cards", a list of easy references providing magnification/exit pupil/field-of-view for every eyepiece for each of my scopes. Also at the bottom a "star-test" guide, showing

1. how many full turns of the focuser's fine-focus knob I need to provide 10 wavelengths of defocus aberration (for star-testing) and

2. how many millimetres of knob-travel I need for 1/8-wavelength defocus (i.e. how far before defocusing should become noticeable, i.e. a depth-of-field distance, in units of knob-travel).

Ably helped hindered by a furry companion...

15 minutes ago, JOC said:

... I thought the standing advice with this sort of thing actually was to pick stars that weren't too close together and hence I've also always picked stars a long way from each other.

that's been my understanding too.

If you choose stars that are close together, I think any error in your centering will be greatly amplified the further away you get from your alignment stars.

If I want accurate go-to, I use a reticule eyepiece to get the stars exactly centred; I do my polar alignment with full load; and before starting I delete any user-settings, such as historical PAE adjustments (which, I understand, effectively tell the handset: "THIS is where the target I chose actually is").

Sorry to hear of your travails Adam.

I haven’t so far had any particularly bad experiences with SGL, or even with ebay, but I have been surprised by others’ attitudes when talking about it. I’ve concluded my half-Finnish upbringing has instilled into me a stronger sense of right and wrong than, for instance, some of my senior colleagues.

One such (very senior) colleague bought an expensive camera lens, £1,000 or thereabouts, on ebay. Shortly after that, he dropped it, cracking the front filter ring and slightly denting it. Discussing this, he said that he was going to simply hawk it back out on ebay. I said something like, “whilst ‘fessing up to the damage of course?”. His response was: no he wouldn’t mention it, as the damage wasn’t obvious at first glance. I was appalled.

Later, I was relating this to another (also very senior) colleague, my point being to highlight what I thought was very, er, poor behaviour. His response was also “what’s wrong with that?”. These were people that I regard as now having revealed part of their souls to me and I think of them very differently from how I had beforehand.

I guess you either have to know your seller, or look closely at any feedback there might be wherever you’re buying.

I had a more extended session observing on Saturday night. Star testing showed vastly better patterns than before, and stars were more or less points, though there's plenty of room for final improvement.

To demonstrate how much better the first rough collimation was, I took a couple of terrestrial photos, "before" and "after" of a pipe about 50m away. The "before" pic is really the very best focus I could achieve at the time. The "after" pic is of the same pipe a few inches down.

I fitted a 239-something o-ring to my 200p, but not to prevent slippage, rather to try to stiffen up the tube near the focuser, as collimation was changing as I changed altitude.

i wouldn’t worry about sufficient grip, I’d worry more about crushing or buckling the tube.

see pic below...

cheers, Magnus 

7 hours ago, Ships and Stars said:

I've never seen a live rocket launch, must be incredible. How frequently do they launch? Cape Canaveral probably? I've some friends that live on the gulf side.

Perhaps you’ll be seeing them before too long, if the Western Isles are getting a new starport 😢?

... it did work well. A very small window in the clouds tonight revealed Rigel, I quickly turned the scope towards it, and Lo and Behold, my stars are pinpoints again. Too much cloud for anything as sophisticated as star tests but gratifying that method gets me close.

bring on clear skies to fine tune...

M

Last night, Friday, was clear so I couldn’t resist a quick session. I took out my little-used Skywatcher Mak 150, Zeiss prism diagonal and Skytee2. On the secondary saddle I added my little Leica 62mm apo spotting scope with its 16-48 zoom eyepiece.

Also, I’ve bought a couple of BST eyepieces as a present to replace the stock eyepieces on my wife’s brother’s (kids’) Heritage 130 and thought it might be fun to test that off against my TV DeLite 18.2

No exotic targets, I was Friday-tired, but an easy session with some interesting comparisons.

- The Moon. 70+%, very high, I concentrated on the Aristarchus area. The Leica as expected showed the whole very crisp, but the Mak 150 with the panoptic 35 was noticeably more pleasing when matching magnification. This would be confirmed more stringently later with Polaris B. Mag at 300x seemed to be the limit of where I could get before losing satisfaction.

Swapping between the BST 18 ED and the DeLite 18.2 showed the DeLite better, as expected, but there was not much in it, and difficult to quantify. Both sharp and contrasty, the TV was simply the one I wanted to look through more. I think my bro in law will be very pleased with the new eyepieces. I seriously recommend them, at £35 second hand or even £45 new they are a true bargain. 

- I moved on to Algieba, 4 seconds or so apart. With a max mag of 48x on the little 62mm Leica I couldn’t really split the double, but with the Mak obviously it was easy. Nice.

- Third and last target, mainly to compare Leica and mak150 at similar magnification on Polaris B. Seeing was not great, star test on the Mak at 300 and 500x was a little too wobbly to be useful.

Nonetheless with the Panoptic 35 on the Mak giving me 51x the little Polaris B was beautifully evident, plain as day, lovely. Whereas with the Leica62 at 48x I could JUST ABOUT, and then only fleetingly, discern it. Fascinating, 62mm vs 150mm light-collection and resolution.

I had planned to look straight up at the Mizar system to finish but I was too tired. I packed up and rolled into bed about 2am.

Cheers, Magnus

18 hours ago, dweller25 said:

@Captain Magenta

I suspect your primary is not pointing directly at your secondary so would suggest you focus (pun intended) on that first.

Looking at the scope from the front in daylight and examining the hall of mirrors may help you to get reasonably good collimation.

Yes the Hall of Mirrors is a bit of a mess. I'm glad I took a look through it as it showed me just how truly bad collimation can destroy an image.

The various methods available around for collimating dual-mirror-adjustables leave me unsatisfied, including the one I've mentioned a couple of times above. They basically all amount to trial and error adjustment of all six adjustment points (i.e. both mirrors) simultaneously: none truly allows for independent collimation of each mirror separately.

Worrying about this, I suddenly had a brainwave. This scope has its secondary mirror set into a "cup" which screws onto a circular boss in the centre of the corrector. I can unscrew and remove that cup, to reveal a circular hole in the corrector. All I need to do is place a (well-collimated) laser in the Back, a translucent disc over the central hole, and adjust the primary until the laser spot is precisely in the centre of the hole in the corrector. I could go even further and drill a small hole in centre of the metal very-close-fitting main front lenscap, and get the beam through that. As I've already aligned the focuser axis with the centre of curvature of the primary, this should get me very close to primary perfection, and I can then proceed with the secondary orientation without worrying about the primary.

(warning: collimation atrocity follows)

I made considerable progress last weekend, which I’ll document more closely (with pictures) later, but for now an interesting update:

I changed my earlier mind and decided to dismantle the whole front assembly: the secondary “boss” and the corrector plate. I discovered a few problems, such as rusty spring-clips for the corrector plate retaining screws and metal-on-glass direct contact between said screws and corrector-glass. I spaced the metal-on-glass with some electrical tape, but there was not much, for now, I could do about the rusty spring-washers.

Once I’d re-assembled everything, I had only about 30 minutes left. I started to collimate but didn’t get very far, especially as both the Primary and the Secondary are adjustable. The “Back” I was using for the collimation cap and to align the focus-tube is the Back I intend to use “in the field”, and is quite wide where it meets the rear of the tube. Hence it was very difficult to get access to the collimation screw-heads, and my primary collimation was consequently rudimentary-to-non-existent. I started to tackle the secondary, but to begin with, no adjustment I made seemed to make any difference to anything. I dismantled it again to see how it worked, realized my error, re-assembled it, and ran out of time. So I just randomly put it back together enough to ensure the secondary was “held”, and gently removed any play with the three grubs.

Tuesday night beckoned clear, and I was tempted to see just what a totally randomly doubly uncollimated (primary and secondary) was like to actually look through. The scope had been outside to cool for 2-3 hours, and seeing conditions seemed quite good.

I chose the 60% Moon to start with. It was definitely the Moon, and small details, craters and ridges, were visible, but features seemed “smeared” top-right-to-bottom-left in a slightly nauseating way. I turned to Polaris next, and My God! I’ve seen Star-Test images of poorly collimated optics before, but nothing like this!

The closest I could get to focus wasn’t remotely a point, not even a spangle, but a LINE (top-right-to-bottom-left). At 250x, that line occupied perhaps 10% of the diameter of view, or around 2 arc-minutes! The “diffraction pattern” at 10 wavelengths intra-focus looked like a very pointed teardrop, and the outer-focus looked like a triangle. Quite amazing, I’ve never seen anything so horrid through a scope. The sketches below show what I was looking at (roughly to scale, 250x mag):

Bear in mind there’s nothing inherently wrong with this scope, I had it side by side with my newish SW Mak150 three weeks ago and they gave very similar views.

I’m going to enjoy spending time collimating this properly…

... and if anyone actually can interpret those sketches, that'd be interesting. I suspect, for example, that the pointy bit of the teardrop is actually the central dot of the diffraction rings, but shifted outside.

2 hours ago, Stu said:

... I have reacquired a Leica Zoom ...

Is that a Leica astro-dedicated zoom Stu, or a spotting-scope eyepiece with special 1.25" adapter? I have a Leica spotting scope and zoom eyepiece, and am dying to use it on my scopes, but the adapters seem very hard to come by!

M

... but hopefully a beautiful enough sight to take the mind off sitting in a queue?

... as they say, what's the best camera when you see something that needs its picture taking? "The one you have on you".

I had to stop a couple of times whilst cycling home this evening, taken on my iPhone. Earthshine only barely discernible unfortunately if you pixel-peep.

If you can try for it during daytime or very early evening, it won't flare as much and the phase should be highly evident.

The problem then is actually finding it in the first place. The technique I use is to fix the elevation of the scope at the altitude my App says it should be, point it in roughly the right direction, and pan from side to side only at, say, 30x magnification to begin with. You should find that bright dot reasonably quickly, then you can start upping the magnification.

Cheers, Magnus

The Start of Re-Assembly and Re-Collimation

This last weekend, and in possession of new pristine nuts, screws and grubs to replace most of the existing fixings, I set about re-assembly and the start of re-collimation.

I smothered the meeting-faces of the two baffle-tubes in silicone grease, having been careful to make sure the brass tab was back in its place, and brought them together. Next I greased and assembled the large white-metal toothed sprocket assembly, the two white plastic brackets and the aluminium ring.

The idea was that the threaded end of the baffle-tube screwed into the two half-threads of the plastic brackets, but it proved rather difficult. I tried several times but it just didn’t want to go in square, it wanted to thread itself at an angle, and I was afraid if I tried too hard I’d damage the plastic threads. I had to think of another way. In the end, I had to re-dismantle the toothed-ring-and-plastic-brackets assembly, and start again by separately placing each plastic bracket directly onto the metal threads on the baffle-tube, made easier by the presence of lots of grease effectively sticking them in place, and then attach the metal ring and toothed gear-wheel in situ. That worked.

Next I attached the black-painted metal rear “hub” to the full back-plate of the scope via my new “pull” collimation screws, and also screwed in the new (nylon-tipped no less) “push” grubscrews. I could then insert the back end of the focuser/baffle-tube assembly into the hub’s recess, partly locking its orientation with a single screw through the side which threaded into a hole in the aforementioned aluminium ring. I clamped the whole thing in place by threading on the white-metal SCT “visual back” from the other side of the back-plate, with a pair of extra pointed grubscrews to lock its position and prevent it from unscrewing while using it as a visual back.

I also re-fitted the focus-knob assembly, comprising an inner thick brass round slug and outer plate, each with 3 holes, which when clamped together from either side of the back-plate allowed the brass slug’s central hole to receive the focus-knob axle, itself attached to and held in place by a small gear-wheel on the inside. The small sprocket’s teeth meshed with the teeth on the huge ring inside, and via the threaded white plastic threads the outer baffle-tube was allowed to slide up and down the inner baffle-tube. Since the primary mirror sits on a flange on the outer baffle-tube, focus is thus achieved.

However, the hole in the brass slug is not quite in the centre, it’s slightly offset, so by adjusting the rotational position of the brass slug, the small sprocket can be adjusted closer to or further from the big wheel, allowing the teeth to mesh more or less closely. Crude, and a bit trial-and-error to get the right position, but it works.

Now it was time to turn my attention to the primary mirror itself, and to start the 3 main steps of collimation (align focus-tube axis to centre of curvature of primary, collimate primary, collimate secondary).

The mirror was reasonably clean, except a ring of greasy dust right around its central hole. I cleaned this away. The primary mirror sits on a flange machined into the outer baffle-tube. Never a good idea to allow direct glass-on-metal contact, there were 3 thin strips of plastic tape going from under the mirror, up the inside of the central hole, and over the top onto the mirror itself. This ensured that the mirror was sitting on plastic tape on the flange, that the metal retaining ring on top was touching tape, not mirror, and that the sides of the 50mm hole in the primary were not directly touching the metal of the baffle-tube.

Unfortunately, when I lowered the mirror over the tube and onto its flange, I noted that there was more “play” side to side than I was happy with. There must be some play, to avoid straining the mirror, but it must be infinitesimal. In the end, I applied two extra strips of electrical tape (0.1mm thick) at three places on the mirror around the inside of the central hole. Finally, I secured the mirror vertically with its two locking rings: the first simply rested on top of the mirror (again, infinitesimal gap) and “grub-screwed” onto the tube, the second threaded down onto that.

Collimation First Stage: Aligning the Focus-Tube Axis Towards the Mirror’s Centre of Curvature.

Following the logic in kitchen table collimation about the preliminary step for scopes with adjustable secondary AND primary, I constructed a makeshift optical-bench setup: A pair of axle-stands each topped with plastic V-pieces; and a “bullseye” target with a 1mm hole in the exact centre with a very bright light source just behind the hole.

The idea is to place the target in front of the primary mirror, which reflects the central light source back onto the target. If things are arranged such that the reflected dot returns exactly back to the light source, the target centre is at the exact centre-of curvature of the mirror. If that mirror is a spherical one, which in this case is likely, then the source-dot and its reflection represent the centre of that sphere. It’s very important that the focuser axis also coincides with that centre of curvature. A laser is used, inserted into the eyepiece-holder at the back of the scope, to check whether the laser spot also hits the sphere-centre. Neddless to say, the laser itself must properly collimated otherwise it’s a waste of time. In my case I was using a 2” Glatter, which I have tested to be properly collimated. If lucky, the laser dot will strike right on the centre of the target/light source.

I wasn’t lucky. In fact Rus Slater, author of the website I’ve been using as a guide, writes:

“Chances are that the laser spot will appear several millimetres off-centre. It now remains to find the source of the error and if possible correct it, noting of course that as already stated the focuser tilt is not independently adjustable on the smaller RC telescopes. Check firstly that the primary mirror is not loose;”

The photo here shows the light source and its reflection exactly on top of each other, but the laser dot 5mm “off”, which seems quite a lot. The radius of my spherical mirror being 800mm, the error amounted to over 21 arc-minutes. I did a bit of testing to see whether anything was loose: all was tight. I rotated the laser in its housing: no change. I rotated the whole scope on my “optical bench”, and the laser dot went around with it. There was no perceptible play in the placement of the mirror itself on its flange.

I didn’t have time fully to investigate the source of the misalignment, that was for the following weekend, but things to explore further would include:

-          Play between the inner and outer baffle tubes

-          Misalignment of the SCT-2” adapter I’d attached to the Visual Back

-          Non-parallel rear surface of the primary mirror

-          Insufficiently-constrained mirror, causing it to “flop”

-          Misaligned mirror-support flange

This was the first really interesting part of this whole exercise: an actual optical problem to fix! Brilliant.

If it was to come to adjusting the tilt of the mirror on its flange, as seemed likely, the solution would be shimming between the mirror and its base-flange, as in this scope there was no other “designed-in” way of adjusting it. An adjustment of 21 arc-minutes across the 40-50mm of the central hole would amount to a shim of 0.25mm or so, in other words two layers of my electrical tape.

Until next weekend...

On 22/02/2020 at 16:09, Piero said:

 

 

Sidgwick's Amateur astronomer's book is excellent in my opinion. Very inspirational and rich of insights. A keeper.

 

Yes I agree, having had a look through it now. An ocean of information. A good companion to Suiter.

Thank you all ... just the advice I was asking for, ES68/24mm + Vixen SLVs upwards is what I’ll recommend

M

... well it turns out that @dweller25 was right after all, my apologies. The focuser arrangement *is* offset, allowing for adjustment of the distance from focus-knob axis to the big sprocket.

Back plate, baffle-tubes and focus mechanism all now reassembled with new fittings, pics and more descriptions to follow...

cheers, Magnus

On 20/02/2020 at 19:43, Captain Magenta said:

A totally unexpected arrival in the post. I have no idea when I ordered it or even any recollection of ordering it. Which means only one thing: 🍺🍺🍺.

Still, I’m glad I did.

 

... as a follow-up to this I thought I might post a picture of the inside-cover page to see if by some happy chance the previous owner is on SGL?

On 20/02/2020 at 21:28, joe aguiar said:

The way I do it may be different than most but this is how I do it u may choose any way u like

I base it on the telescope price so for a 130mm reflector that's like a $200price point, I would only buy plossls/ super plossls  maybe bst or something like Meade HD 60 fov 5000 eps.

Joejaguar 

Joe thanks - in general in life I agree with you, matching components on any system, be it hifi, bicycle, new kitchen or whatever, you get what you pay for and it makes sense to balance the "what you pay" accordingly. But in astronomy equipment, I do find this rule gets broken a bit. With something like the 130p you seem to get, for the mirror at least, much more than you pay for, but for the accessories, less. So I do think it justified to up the spend a little on the eyepieces for such a mirror, because the OEM ones are so poor, but obviously not to the level of Delos etc. So your suggestions of Meade HD 60 or BST are about right.

Any othres in that category that stand out? Vixen? APM? ES?

Cheers, Magnus

I must admit I do notice a difference when shielding my Sqm-l just with my hand from my house lights when taking readings. If you could rustle one up for me too I’d be grateful ... 😬

M

Hi all,

A colleague of mine has a f/5 SW 130p and still uses the original eyepieces. He knows it's a fine telescope, but he wants to upgrade the eyepieces. He asked me for advice.

I told him it very much depends on his budget: £900 per eyepiece gets him TV Ethos, £250-300 gets him TV Delos or Delite, £100 gets him [  Baader Hyperion?  ], £40-50 gets him BST Starguider. I'm not that experienced and went straight for TV Panoptic/Delite/Delos so I can't really help him.

He said he'd be looking for perhaps 3 eyepieces, in the £100 per eyepiece range. What's best at that price point? He does not wear glasses to observe.

Advice gratefully received...

Thanks, Magnus

A totally unexpected arrival in the post. I have no idea when I ordered it or even any recollection of ordering it. Which means only one thing: 🍺🍺🍺.

Still, I’m glad I did.