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Captain Magenta

Intes M603 Tear-Down Refurb & Re-Collimation

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I recently acquired an Intes 6” Rumak Maksutov Cassegrain telescope, seduced by rumours of their famed optical quality. The Rumak-Mak differs from the more familiar Gregory-Mak (such as Skywatcher’s) by having a separated and adjustable secondary mirror attached to the front correcting lens, rather than a Gregory’s non-adjustable mirrored spot. This allows more degrees of freedom for the optical designer, and the possibility of correcting a wider range of aberrations.

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The scope was clearly quite old, but in reasonable shape, in particular the primary mirror and corrector plate which both looked immaculate. It came with a steel screw-on baffled dew shield, somewhat rusty on the inside, which must have been sat on at some stage of its life: it was bent into an oval at the open end. Leaning on it again and a bit of micro-surgery with pliers sorted it out.

All the visible screws on the scope were such as would not be used today, a combination of soft worn slot-headed screws and part-rounded-out Philips-heads. Most of the screw-heads in fact, both for collimating and holding things together, had signs of lots of use and wear. I was worried I wouldn’t get enough purchase on some of them if they proved stiff.

The focuser comprised a knob on the scope’s back plate, in common with all other SCTs and Maks I’ve seen. However, in use it was horrible: lots of slack, wobbly and clunky.

A couple of sessions looking through the scope confirmed that I was going to have to collimate it, even though I did manage to see Mercury’s 50% phase one evening in Feb 2020 through a mask of trees. A Rumak’s adjustable secondary AND primary meant that collimating a scope like this was going to be not dissimilar to collimating a Ritchey-Chretien: difficult, but rather important for best performance. Perfect, because I love technical challenges like this. This scope had obviously had some fairly heavyweight “collimation” done to it in the past, to judge by the worn state of its collimation screws!

To collimate either mirror using the six screws for each meant I would need to know exactly how it was put together and what each screw actually did. Were they “adjust-and-lock” or “push-pull”? The only sure way to find out was to take things apart and have a look.

The combination of all fixings being tarnished and worn, a focuser in desperate need of servicing and my need to find out how the collimation adjustments worked, meant only one thing: Complete Tear-Down. Genuine Yipee.

Tear Down

Interestingly, the other thread on CN describing an M603 disassembly, https://www.cloudynights.com/topic/580999-intes-micro-alter-m603-dissection/ , shows that our two scopes, despite having the same designation (Intes M603) have some quite big differences, especially in the focus-knob area! I think mine is significantly older. I couldn’t find any date-marks anywhere when I took it apart, but the rear of the primary mirror did have a hand-written “No. 117”. Hopefully between these two threads, all bases can be covered!

My strategy was:

-          Take everything to bits

-          Replace all screws, grubs and bolts with new stainless-steel torx or hex fittings

-          Clean and re-lubricate everything

-          Reassemble

-          Re-Collimate

Informal Description with Pictures

The following steps and pictures paint an informal picture-guide to the tear-down. Later on I’ve assimilated this into a series of more detailed formal steps which will be useful in reverse when it comes to re-assembly.

The rear plate was removed from the main tube by unscrewing six slot-headed M4 countersunk screws, all of which moved and came away easily. This revealed a double baffle-tube, a large toothed ring and the primary mirror, all sticking up from the centre of the main rear plate.

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The inner baffle tube, the longer of the two, was screwed directly into the external flanged “back” at the rear of the scope, which was in turn attached to the actual main rear plate of the scope via three pairs of heavy-duty collimating screws. Fiddling with these six collimation screws therefore changed the orientation of the whole main baffle tube with respect to the main back plate: it was this mechanism that collimates the primary mirror. Some of these screws had obviously been heavily used with much torque!

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Around the outside of the inner baffle tube sat a shorter outer baffle tube, which had a raised flange 2-3 cms from the rear plate, on which sat the primary mirror. The large toothed ring beneath it allowed the outer baffle tube, and hence the primary mirror, to slide up and down the inner one, driven by the external knob and a little gear plus a threading mechanism.

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The primary mirror was held onto its flange by two retaining rings sitting atop it, each held in place on the baffle tube by a tiny grubscrew. The retaining ring closest to the mirror had its own flange.

The size of the primary mirror can be seen in the picture of me holding a set of micrometer jaws set at 150mm: the scope is specified at 150mm, so the mirror is considerably oversized.

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Removing the mirror revealed a ring of some sort of contamination around its central hole. It turned out this was greasy dust on top of the mirror, not under the coating thankfully.

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The mirror off, and the focusing mechanism was revealed: crude but effective, assuming I could get rid of the wonkiness and tooth-slack.

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The back half of the scope all came apart rather easily and intuitively. Good.

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Almost everything, barring the mirror, now went into my Ultrasonic Cleaner. Those two whitish plastic brackets were almost black in parts when they went in!

Next I removed the front bit from the main tube: the Corrector Plate assembly and Secondary Mirror holder. These six screws were worn-out Philips-head screws, and one was quite difficult to get moving. But the front plate came off easily enough.

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Disassembling the secondary mirror assembly proved ostensibly simpler but rather more risky. The front plate comprised six collimating (push-pull) screws, three cap-head and three grubs, and a central locating-pin. The three cap-head screws were completely loose, although the heads showed signs of wear! They were so loose I could undo them with my fingernail, and they were the “pull” screws, threaded directly into the secondary holder itself. The three smaller screws, grubscrews, were very tight and quite difficult to remove without damaging the slot-heads. I had to proceed very slowly and carefully. Once all were free, the front plate still wouldn’t slide off. I noticed there were three further tiny pointed grubscrews on the SIDE of the cylinder, holding it in place. Two came out perfectly easily. The third one, however, took ages. The slot-head was far from centred on the top of the grubscrew and I had to be VERY careful not to simply tear the thin part off with my precision screwdriver. But I got there eventually.

I have to admit I baulked at removing the Corrector Plate (the big lens on the front) from the scope’s main front ring. It was not designed to be adjusted and looked perfectly good to me.

The secondary mirror, once removed, had some similar contamination around the edge to that of the primary, but again I ascertained it was on top of the coating not underneath, and hence easily removable. Also, the central locating-pin was rather rusty.

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The mirrors and corrector plate went into protective custody, as shown, and the remaining parts now reside in a cardboard box, awaiting my 50-odd miscellaneous new stainless screws, grubs and bolts from accu.co.uk.

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Formal Description, in Steps:

i.                     Remove the 6 countersunk screws holding the main rear plate to the main tube;

ii.                   Notice the two retaining rings around the baffle tube sitting atop the primary mirror: they are each locked in place with a tiny grubscrew. Loosen these tiny grubscrews and lift the rings off the baffle tube (note that the one next to the mirror itself has a small flange – this sits adjacent to the mirror);

iii.                 Remove primary mirror and set it aside;

iv.                 Main rear plate central hub: unscrew and remove all 6 screws from the back plate (3 large, 3 smaller) – these screws hold the hub to the rear plate and also act as the collimation mechanism; Also notice and remove a single screw on the side of that hub, just next to one of the pairs of holes. This screw screws into the aluminium ring holding the plastic brackets, and effectively locks the non-moving part the baffle-tube focus mechanism;

v.                   Unscrew the silver-metal “back” from the rear central external “hub” – take care, as this is what secures the whole baffle-tube assembly to the rear of the scope. Hold the baffle tube as you unscrew;

vi.                 Remove and set aside the main rear plate, the black “hub” and the white-metal rear securing “back”;

vii.                The large toothed white-metal disc: the plastic brackets attached to this disc contain a coarse thread which meets a thread all around the outside of the black baffle tube. Unscrew the big disk all the way off the tube;

viii.              Dismantle the toothed focus-ring by unscrewing the 4 screws securing the whitish plastic brackets to it. The brackets will come away, together with the aluminium disc securing the white brackets. NOTE THE ORIENTATION OF THE SINGLE THREADED HOLE IN THAT ALU RING, IT’S OFF-CENTRE TOWARDS THE BACK END OF THE SCOPE.

ix.                  The inner and outer baffle tubes: notice a single screw, in the pic next to the number “19”. The screw attaches inside to a small brass sliding block which slides up and down a guide channel in the inner baffle, keeping the two tubes aligned as the outer mirror-holding tube slides up and down for focus. Be careful not to drop and lose the small brass notch when you separate the tubes!

x.                   Front of scope: unscrew and remove the six countersunk screws attaching the front plate to the main OTA;

xi.                  Secondary mirror: unscrew and remove all 6 collimation screws from the collimation plate, keeping the front plate upwards to avoid things dropping out;

xii.                With a long precision screwdriver, loosen the three tiny almost-invisible sideways-pointing grubscrews, which lock the secondary collimation-plate in place. Be careful not to touch the corrector plate while doing this.

xiii.              Lift out the front plate, to reveal the back of the secondary mirror itself;

xiv.              Carefully remove the secondary mirror, and escort into protective custody;

xv.                The End.

Re-Assembly and Collimation

Watch this space…

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Edited by Captain Magenta
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Enjoying coming along for the ride on this one - great write up!

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Great writeup @Captain Magenta- How is the dovetail attached to the OTA ?
Mine was attached with pop rivets which were loose - they were all removed and replaced with stainless steel nuts and bolts.

 

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3 minutes ago, dweller25 said:

Great writeup @Captain Magenta- How is the dovetail attached to the OTA ?
Mine was attached with pop rivets which were loose - they were all removed and replaced with stainless steel nuts and bolts.

Good question, I haven't paid any attention to the actual steel tube yet, apart from a bit of bending on the dew-shield. While I await my fixings to arrive, I'll take a look at that. Pop rivets certainly won't do!

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The focuser is set on a lobal cam, so to take up any slack it just needs to be loosened and rotated slightly 👍

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5 minutes ago, dweller25 said:

The focuser is set on a lobal cam, so to take up any slack it just needs to be loosened and rotated slightly 👍

I saw that from the CN thread too, and checked mine out once I'd dismantled it, funnily enough I don't think mine is cammed, everything is quite circular. I'll check again but I suspect that arrangement might have been an upgrade from when mine was made...

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Fascinating read, and full respect to you for having the skills and pluck to do this!

I owned 2 M603's and a Lomo Astele Mak 150mm a few years ago and was very impressed with them all optically. They always seemed built like tanks and very industrial, but optically superb, especially on Lunar, Planets and Doubles.

I'm sure that, once you have worked your magic on it, yours will perform like a champion!

Thanks for sharing 👍😊

Dave

Edited by F15Rules
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5 minutes ago, F15Rules said:

Fascinating read, and full respect to you for having the skills and pluck ...

Dave

:) Only pluck demonstrated so far! Skills remain to be seen. Fingers crossed!

M

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Fantastic. Following this with great interest.

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My fixings arrive on Monday, so I'll have to wait until next weekend to start the rebuild.

In the meantime, after @dweller25's mention of the dovetail and how it's attached, I had a look. Although the screws are just as old and shoddy-looking as the rest, they are doing a good job securing the dovetail to the main tube. There's a pair of bolt-and-nut arrangements at each end, and a line of screw-in bolts all along the bar, all secured with a longitudinal strip inside the tube. They also double up as internal baffle-ring holders. Similarly the finder fixing arrangements: built like a tank.

I think I'll leave all that as is for the time being, though I may upgrade to rings in due course.

Photos documenting the same:

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(actually @Richard136 might be interested in this ;) )

Edited by Captain Magenta

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... while I await the arrival of screws bolts etc to reassemble the scope, I though I might make up my collimation kit and do a bit of practise on my Skywatcher Mak 150.

I plan to use the technique called "kitchen table collimation". Accordingly, I built myself a target, a square of thin ply, with the target taped to the front, and a 1mm pinhole at its exact centre with a head-torch LED right behind it. To constrain the very bright source to just the pinhole, there are 2 layers of black tape and a layer of Aluminium foil between the middle of the target and the hole in the ply.

The idea is that the pinhole source gets reflected back by the primary mirror, and you line everything up by placing the reflection back on top of the centre of the target. This ensures the target is precisely in line with the optical axis of the primary. Then you look through a collimation cap at the back of the scope to see whether all those rings are concentric.

Luckily, in this case, it was all spot on. My *Skywatcher* Mak 150 needs no adjustment.

A very useful exercise ahead of doing it all from scratch for the Intes.

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deliberately slightly offset here to show the source and the reflection back onto the target:

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Edited by Captain Magenta
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... fixings have arrived. The process of ordering them was amongst the most pleasurable ways I've spent the best part of £12! I thoroughly recommend accu.co.uk! And I expect they will have a disproportionate effect on the value of this scope, not that I have any plans to sell it...

 

StainlessFixings.jpeg

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Great post and very interesting. I would never be brave enough to take that apart!

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... 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

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1 hour ago, Captain Magenta said:

... 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

👍

Edited by dweller25

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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.

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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.

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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.

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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.

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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.

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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;”

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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...

Edited by Captain Magenta
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Posted (edited)

(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):

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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.

Edited by Captain Magenta

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@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.

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Continuing to follow with great interest. I definitely take off my hat to you for having the confidence to strip the scope so far and knowing how to get it to go back together.
I am certainly regarding this thread as having good reference material if I ever need to tear down a similar scope.
Or maybe I could bring the scope to you with a crate of beer.😁

Thanks for keeping us so well informed as the project moves forward.

David.

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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.

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Posted (edited)

That is exactly what I did - it worked well 👍

 

 

Edited by dweller25
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... 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

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