Recovering an Ebay TSO

[RLWP]

Ohh, the curse of Ebay. I have bought an 8" reflector for £32. One picture and a brief description - and it was local

It would be fair to say the seller was a little economical with the truth. Yes, it did have a dent in the tube. Yes, the mirror did need some adjustment. No mention that it had been dropped, the mirror had popped out of one of the clips, the focuser had severely distorted the tube...

Ho hum. So I took it to bits, gently knocked the dents out of the tube and I have painted over the horrible sprayed black paint:

It's a Konus Konusky 200 Motor (well, it was, I only have the OTA and finder scope) 200mm mirror, F5

Watch this space for more fun

Richard

[knobby]

I love a challenge ! keep us posted 

[ronin]

Well look upon it that they would have got £32 had they advertised it as Spares or Repair.

It will occuply you on the cloudy nights we get, so you should have it all done in less then a week. :grin:

[RLWP]

Like any of these basket case projects, you don't half learn stuff quickly! I'm reading around collimation, alignment and stuff at the moment

Richard

[michael.h.f.wilkinson]

That looks like a project and a half. Best of luck!

[RLWP]

I'm hoping that there's a reasonable scope in here somewhere.

My biggest concern is the mirror. Reading around Konus Konusky 'scopes, some used spherical mirrors (!). How can I tell if I have a spherical or parabolic mirror?

Richard

[damnut]

At least it was not a Seben.

[Laurie61]

I'm hoping that there's a reasonable scope in here somewhere.

My biggest concern is the mirror. Reading around Konus Konusky 'scopes, some used spherical mirrors (!). How can I tell if I have a spherical or parabolic mirror?

Richard

You could try this to test for mirror figure.   http://en.wikipedia.org/wiki/Foucault_knife-edge_test 

[RLWP]

You could try this to test for mirror figure.   http://en.wikipedia.org/wiki/Foucault_knife-edge_test

Brilliant - thank you

Richard

[Gazabone]

Good luck, I bought a duff C8 last year from eBay (sadly paid rather more than £32 for it!). Think it will need more accurate tweaking than I'm capable of. An out of focus star appears as a blurred figure 8 (no exaggeration at all), in focus it is a / not a point of light (again, no exaggeration). I know now that the corrector plate is not original to the tube and have a feeling perhaps it's not exactly parallel (if that's what it needs to be).

As I said, good luck with your project, hopefully you'll have a great scope at the end of it.

[RLWP]

Good luck, I bought a duff C8 last year from eBay (sadly paid rather more than £32 for it!). Think it will need more accurate tweaking than I'm capable of. An out of focus star appears as a blurred figure 8 (no exaggeration at all), in focus it is a / not a point of light (again, no exaggeration). I know now that the corrector plate is not original to the tube and have a feeling perhaps it's not exactly parallel (if that's what it needs to be).

As I said, good luck with your project, hopefully you'll have a great scope at the end of it.

I enjoy the story telling part of my adventures, maybe you'll find something to help you out with the C8 along the journey

Richard

[RLWP]

Another coat of Bootslack* on the tubes.

Why - how - what?? There's no crosshairs in the finder scope! There are notches to align the wires but nothing fitted. So, synthetic thread, sticky tape and glue:

The tape is to hold the thread tight while the glue sets. Trap one end of the thread, run it across the eyepiece, pull tight and anchor the other end with tape:

Synthetic thread as it isn't hairy like ordinary cotton is. This thread might be a bit thick, good enough as a starting point though

Richard

*Bootslack. I'm using up a tin of yellow Epifanes paint, bootslack is German for boat paint (on the label)

[John]

Interesting purchase.

My money would be on it being the same scope as the Skywatcher / Helios Explorer 200mm F/5 so it will have a parabolic primary mirror.

I used to have a Konusky 150 F/8 refractor which was exactly the same scope as the Skywatcher / Helios Evostar 150 F/8 refractor except for the "lovely" orange / yellow colour scheme !

I used fine fishing line to replace the "hairs" in a finder once and that seemed to work OK.

[RLWP]

Fishing line makes sense, I would have used invisible thread if I could have found it (add your own jokes here)

The Prinz scope has some kind of transparent thread painted black, with some of the black missing. It looks very weird if you concentrate on it

Richard

[Peter Drew]

The Konus telescopes actually have quite decent optics, although from the "usual" sourse there is an urban myth that Konus cherry pick them. We have a donated Konus 114mm F8 Newtonian which gives fine images. 

Ref. the post about the duff C8, sounds to me like a broken corrector being replaced by a disc of window glass. 

[John]

Thats true Peter - some with the Konus branding on are not so good. Thinking back I also had an 80mm Konus F/5 refractor which seemed to be an ST80 clone but some of the ones in their blue colour scheme didn't seem so appealing.

I've heard of the window glass SCT corrector trick before and it's a really mean trick to pull

[RLWP]

So, the original bilious orange of this Konus might be a good sign

AIUI, the Skywatcher scopes have springs under the mirror cell that the collimation screws work against. Is that right, and are they available anywhere?

Richard

[RLWP]

Front ring with collimation screws (home made) and a coat of blackboard paint on the inside to cover the scratches

Richard

[John]

Interesting. The style of those secondary supports and secondary hub is as per the very early "Helios" branded 8" F/5 newtonians. It's possible that back then they used a different design mirror cell to the more recent ones as well, perhaps using rubber spacers instead of collimation springs or even an unsprung "push-pull" system ?

[RLWP]

Yes, it's an unsprung push-pull with six cross-headed screws. I'd like to replace that with something friendlier

Richard

[RLWP]

I have stored the tube in the greenhouse to allow the paint to harden - and lodgers have moved in!

Richard

[RLWP]

OK, lodgers evicted

As the clips no longer held the mirror into the cell, I have dismantled it. The mirror was held down by rubber pads with a metal pad on top and screws. When it was dropped, the mirror moved sideways and bent the screws. The mirror would just come out of the cell with the retaining pads in place, so I took it out and wrapped it in bubble wrap until I need it.

I tried to undo the screws, (following in the footsteps of a previous astronomer judging by the damage to the screw heads) with no luck. In the end, I trapped the heads in a vice and turned the cell. One screw came undone, the rest sheared off. The softness and colour would suggest these screws were stainless.

Trying the mount into the lower ring, I found that when fully in, it would stick!:

I suspect in the normal range of adjustment, this isn't a problem. Just in case, I skimmed the outside of the mount:

I have also filed down the sheared screws and turned the outside of the mirror retaining lugs. I'm going to attach new clips to the outside of these lugs

To make clearance for these new clips, I have flied out the slots in the lower ring:

So, now I have a freely moving mount in the lower ring, with clearance for new mirror retaining clips:

I'm thinking about collimation screws next

Richard

[RLWP]

I'm familiar with Astro-Baby's excellent collimation guide, I can see it is going to be useful so I have printed a copy

At the moment, I'm using Nils Olof Carlin's guide here: http://web.telia.com/~u41105032/kolli/kolli.html. It contains a lot of design detail that I need. 

I've taken something about focuser alignment from that, it's likely to be out as the tube was bent. So, I've put a hole in the tube directly opposite the centre of the focuser hole.

I ran a piece of masking tape around the tube and drew a line on it from the centre of the hole:

I used a pair of dividers adjusted by trial and error to give twelve equal steps from one side of the hole to the other (guess a size, step around, estimate a twelfth part of the error, try again and repeat until it is correct - it really doesn't take long). Stepping around six times gives me half way around. I checked  by stepping from either side of the focuser hole - I was dead on.

Next, I drilled a 1mm hole

Here is the hole illuminated:

It's actually hard to find on the other side, so I have marked it's location:

Richard

[RLWP]

Thinking ahead a bit. This 'scope has already crashed to the floor once because of an inadequate mount (which I do not have, fortunately). So, what should I be mounting it on? Preferably I'd like an EQ mount, not too bothered about GOTO at the moment

How do I set about selecting a mount - weigh the 'scope?

Any suggestions?

Richard

[Joseki]

Great thread btw, as for mount just check out what other people are using for 200 f5 newts - i.e. EQ5 or (better) HEQ5.  If you're not bothered about goto you might be better making a dob base though.   It wouldn't cost much to make and you could see how you like the scopes performance.