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markse68

The joys of owning an old banger of a scope

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I’ve spent the day “upgrading” my new old scope- it’s so liberating to own something like this that’s not too precious! A bit like an old car where you don’t cry about every dent or scratch, I can drill new holes to mount things without a care 😊 (it’s already full of old holes 😉)

First up- modifying the secondary spider. This needed to be done as after collimating, the secondary wasn’t anywhere near concentric with the reflected image of the primary centre spot and the eyepiece barrel and there was no way to adjust it. The spider had its vanes bent at the ends then screwed crudely to the main tube. I hacked the ends off then extended them with studding and thumb nuts so the secondary can be adjusted laterally. After the last pic I sprayed it all Matt black. It’s surprisingly solid when the thumb nuts are nipped up.

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Then the primary mirror cell- hopefully this will fix the problem I had of losing collimation when taking the scope in the car to a viewing site. The original springs the wing nuts compressed just felt a bit too soft and it was too easy to knock the wing nuts loading the scope into the car. I found some stiffer longer springs which needed cutting down to size, and I fitted thumb nuts in place of the rusty wing nuts- M6 tapped to 1/4 UNC to match the studs. It certainly feels more solid now

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Next the finder- I quite liked the Fullerscope one but it’s huge and has a very narrow afov and very crude wobbly wire crosshairs. The one on my Tal-1 has a much wider afov, nice crisp crosshairs and a brighter clearer image. I picked up another on eBay last week so on it went. Being much shorter it also means less head movement from eyepiece to eyepiece when aiming 👍

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Coming along nicely chap. Excellent stuff.

Out of interest, where did you get the split threaded studs for the secondary support, or did you make them yourself?

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Nice upgrades!. I enjoy the same thing, old kit  - new life projects. Thanks for sharing. Rob

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Great project, nice to see someone using his diy skills to good use. You can't beat a good Tal finder, the optics are so good. Btw, love the old r&p focuser :)

Steve

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Thanks all😊 It’s just some M6 brass studding  I bought on eBay slit with a junior hacksaw Stu. Fresh blade gave a kerf of about 0.7mm. The vanes  are 0.8mm so the slits needed opening up with some coarse wet and dry.

Yes Steve the Tal finders are very nice- very light too despite solid build. I too really like the old focuser- there’s no slop in it whatsoever. I just got a good deal on a Moonlite and was planning to replace it but am having second thoughts 🤔 I have a nice wide angle TV Widefield 2” which I’ve been wanting to use but the blue anodised Moonlite will look very out of place on this old banger 😂

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Great stuff, the Tal finders (like most things Tal) are optically very nice and well engineered.

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That is just like my old 6" that was the first "propper" scope I had. Bought pretty much all the "bits" from Brunnings (Remember them?) in Holburn. I still have most (Or all) of it. Must get it back together again.

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Day 2- first up sorting out the azimuth bearing on the ancient dob mount. Originally it was 3 blocks of nylon (It looks like ptfe but it seems a bit hard so I’m going with nylon) running on Formica. It worked...kinda. A lot of stiction made it a bit of a pain - movements were hit and miss and jerky resulting in lots of eyepiece shaking.

So I bought and fitted a lazy Susan bearing- made in the USA no less!  A layer of thin rubber couples it to the top part of the mount. I left the 3 original feet as they add stability gliding just over the surface lifted by the bearing.

Much smoother but now the opposite problem 🤦‍♂️. Slightest gust of wind and the tube spun off! 

So today I fitted a brake- a simple affair consisting of a block of nylatron on the end of a piece of studding screwing through a steel thread insert inserted in the moving part of the mount, bearing down on the Formica inside the lazy Susan. Works a treat 😊

I need to be able to split the base to fit it in my car so I’ve fitted a hefty 16mm central shaft and a quick release collar that locks the 2 parts together when in use

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Next up the secondary mirror mount. I wanted to re-stick the mirror as I had seen some double imaging at high power and figured the way it was stuck might be leading to it being slightly bent when the mount was nipped up tight. It was stuck with a layer of double sided sponge tape across its whole back surface and the aluminium support plate is quite thin so must flex some.

The actual mount looks home made but I like it a lot- it’s quite ingenious separating tilt and rotate/height making collimation a doddle. 2 screws are captive in the mirror support plate but able to rotate. They are threaded through the main block with knobs in the outside to adjust. Counterintuitively you must “undo” them counter clockwise to lock position as they pull on the plate. This takes a bit of getting used to. The mirror on its support tilts over a steel pivot bar. Clever I think 👍

To relieve the bending pressure somewhat,  after cleaning off the old tape I just used 2 narrow strips of UHB tape- a super sticky dense semi-sponge tape that should hold it- I hope 😉

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Couple of small bits to finish- I fitted a magnetic tool rack to the back of the tube for a counterweight- the tube can slide in the mount but it’s stiff and the weight should be quicker and easier. It’s a really strong magnet- lucky my car’s aluminium!

And I made a collimating cap that doubles as a dust cover for the focuser in delrin with a retro-reflective ring which, with the retro-reflective centre spot I put on the primary, aids collimation greatly

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So all done for now. Collimation was a joy and everything lines up properly now. I seem to have developed a bit of a thing for Russian scope stuff...Do skorogo comrades ✊

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Well done! My forays into astro' diy are humbled by your work here but there is something very satisfying in tailoring things to your own requirements and it all working out well.

Edited by Alfian
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I feel ashamed now, that my Olde Fullerscope is currently working as a clothes rack, stood on end along side my bed at our Luxury Cumbrian Villa!

It's covered by a thick polythene bag but I'm sure that it's out of collimation with all the disturbance it gets. Luckily it only takes 10 minutes, rack-of-the-eye to get it good.

But still it's no way to treat the old chap!

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Lovely job @markse68

I used to have a Fullersopes finder on one of my old scopes. The one good thing about it was the locking nuts on the finder holder. This meant that once you had aligned the finder, all you needed to do is to tighten the nuts and it would remain aligned. This is a nice refinement that most modern finder mounts don't have - although those on my Tak 10 x 50 and 6 x 30 do.

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Thank you for sharing this with us. Even taking individual items you mention, it is an excellent lesson in how we can overcome failings or weakenesses in our scopes.
The lesson that there is no need to run out to buy this years 'shiny new one' is not lost on me.
If the 'bits of glass' are good then most other problems can be overcome.

Thanks, David.

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Thanks for all the kind words 😊 Yes Alfian making something bought your own gives you an attachment to it and satisfaction in using it I think, and for me having something that’s not too precious- that I can fix if needed is really liberating too. Of course the ultimate would be making from scratch, but that takes more time 😉

I managed to get a couple of hours with it last night- seeing wasn’t very good and it was a bit gusty so good testing conditions for the az bearing/brake. I think it’s about perfect now. There was no tendency to swing in the wind, just eyepiece instability, and I was able to track targets using only eye socket pressure on eyepiece 😂

However to my dismay on arrival at site collimation was off again so my spring upgrade didn’t fix that and I still need to figure out what’s shifting. On the plus side the retro reflective primary spot and collimating focuser cap meant I could quickly get it true again using just the light from my phone startup screen- clear bright circles to concentricise if that’s a word 

Actually I’ve been wondering if using the finder scope might be a more accurate way of getting collimation corrected in cases like this? I had my finder and red dot pretty accurately aligned in the workshop but after recollimating in the field they were both slightly off. If I tweaked the primary to get the eyepiece view aligned to them again I think that’d probably be more accurate than getting the circles concentric by eye over a much shorter distance? I guess provided it’s only the primary that shifted and collimation was perfect when the finders were aligned

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Going for a major overhaul- replacing secondary and fitting 2" focuser. It'll take a bit of time as I'm going to make a new secondary holder but I just ordered a protostar mirror (toss up between Protostar and Antares but Bryan answered email immediately and yet to hear from Antares a week later so...) so I'm commited now

Reason for replacing secondary is my current one is 1.75" and is positioned so the focal plane is a whopping 120mm from the tube. That's a 20% diameter obstruction so not bad but I figured if I went for 1.52" I could move the focuser up 25mm and shorten its protrusion correspondingly, plus a lower 18% obstruction won't hurt given it's quite long f7.3. Also I have a bit of annoying astigmatism at high power. Inconclusive testing with optical flat for fear of damaging the coating but rotating the primary didn't seem to rotate the astigmatism so I'm hoping a new sparkling high precision mirror will improve matters. Plus old secondary should really be re-coated anyway as it looks pretty poor surface finish under microscope so may as well replace it.

Modelled the scope up in solidworks and I'm fairly confident it's fairly accurate now after much measuring

I picked up a great deal on a moonlite focuser but its meant for an SCT so has a very short focus travel and a longer tube for it was 50$ postage alone (!!) so I've calculated its position to allow most of my current eps to focus though some will likely need rings making or pulling out a bit- no big deal really. I don't think Ron at Moonlite was very impressed with the plan though... It's a bit daft really but too much of a bargain so I'll make it work. The focuser base will be 3d printed in nylon

 

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This looks like my first decent telescope which I still own which is a 6 inch b class fuller scope newtonium a great telescope 45 years  ago  it has been around the world and has given great enjoyment and still does

 

 

 

 

 

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I’ve been busy on a major upgrade for my old banger for what seems like absolutely ages... but tonight it’s finally come together! It all started with wanting to swap the 1.25” focuser for a 2” and finding a Moonlite at a good price cemented that idea.

But then I decided if I was going to do that I should swap out the secondary as the old one had a poor surface and I reckoned it could be improved on.

And if I was going to do that I really needed a new secondary mount/spider as the old one while quite nice in principal was the wrong size...

Then I saw someone with a manual motorised focuser and that seemed like a good idea but I figured making my own would be the impetus I needed to finally learn Arduino...

So after many moons I’ve finally ended up with a nice 2” focuser with stepper focus motor (will finally be able to try out that Siberia Erfle @Stardust 😉)

 

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And a beautiful new Protostar quartz secondary mirror in a new mount and spider

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Now I just need some clear skies for its first light

Trouble is- it doesn't feel like an old banger anymore 🤦‍♂️ I’ll be gutted the first time I clonk that moonlite loading it into the car- think I need to make some sort of protective cover

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Edited by markse68
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I am now fairly convinced that the plastic tube of my Fullerscope is a bit of a problem. Ultimately I'd like to replace it with an aluminium tube but that will have to wait- I'm thinking of making a lighter weight aluminium structure dob base for it too... There won't be much original left apart from the main mirror!!

The trouble is the cool down time and the thermals that seem to be present in the tube even after an hour in the cold that must disrupt sharp imaging- in fact I'm now wondering if they were contributing to the astigmatism I was seeing trying to split doubles at high mag.

This is what Polaris looks like slightly de-focused at 340x

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That's at first setup so a bit unfair- as it cools the diffraction rings become clear but are still swimming about.

So in the meantime I've decided to make a cooling fan arrangement for the existing tube. It'll primarily speed up the cooling of the primary but the air will then travel up past it and flush the tube with cool air.  Hopefully it'll improve things!

It'll be powered by 3 Li-ion batteries (I wanted to use a Makita battery but it won't fit) and a PWM fan speed controller will drive 3x 80mm quiet pc fans. It'll all be mounted on a perspex disk and will attach to the collimation knobs using velcro inside the 3 counter-bored posts- I need it to be easily removed as I always need to tweak collimation after driving to my observing site with it in the back of the car.  I've ordered the parts- just need to double check a few dimensions.

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It should all sit just inside the bottom edge of the tube so I can still stand it upright for storage with the fans in place

 

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Edited by markse68
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Pleased with how it came out. It’s a bit heavy but that nicely counters the weight added at the other end by the new focuser etc (and the huge 40mm ep I have!) The fans produce plenty of flow at max speed and can be turned down to silent temp maintenance speed once the scope has cooled properly.

Hopefully it will make a difference!

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Edited by markse68
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Fitting the cooling fan unit last night revealed just how unlevel the primary mirror cell was! I suspected as much as the collimation adjuster screws were very uneven adjusted to get good collimation. So today I’m taking the opportunity to move the cell further up the tube a few mm to give a bit more clearance on the cooling fan unit, whilst reinforcing the holes with large SS washers and getting the holes better levelled. 

The unlevelness was not a surprise once the cell was removed- over the years of this scope’s life it has had many incarnations- several previous different sets of holes were evident, filled with epoxy, and the current holes were a mess!

The washers were bent to fit the tube curve better and glued with Araldite 2031- a slow cure epoxy which remains slightly flexible when cured for a very strong bond. It’s black- I think they add butyl rubber- smells like it anyway.

Old holes were masked on the inside of the tube and filled with the glue. Once cured (tomorrow probably) I’ll drill through the holes in the washers for the new mounting holes.

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Edited by markse68

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On 08/12/2019 at 22:43, markse68 said:

am now fairly convinced that the plastic tube of my Fullerscope is a bit of a problem. Ultimately I'd like to replace it with an aluminium tube but that will have to wait- I'm thinking of making a lighter weight aluminium structure dob base for it too... There won't be much original left apart from the main mirror!!

The trouble is the cool down time and the thermals that seem to be present in the tube even after an hour in the cold that must disrupt sharp imaging- in fact I'm now wondering if they were contributing to the astigmatism I was seeing trying to split doubles at high mag.

I think the plastic will be better than aluminium for thermal management, as the alu would radiate heat quicker?  I'm not sure.  Best would probably be sonotube or hollowcore CF.  Cheapo solution would be self adhesive cork all over the sky facing side of the tube! 

Saying that I think the fan arrangement you've made will manage the thermals effectively (great work btw!).  I have a single large fan (120mm) mounted behind the cell on mine.  I think airflow moving up the tube helps to 'suck' the boundary layer off the primary and also pushes the micro boundary layer off the secondary too.  I am considering two small side mounted fans to blow across the primary but need to figure out a way to mount them and mechanically isolate from the tube.  

Do you get any vibration from your fans transmitting to the mirror cell or does the velcro help to isolate it?

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