yuklop

Morning All, I am hoping experts on here have some good ideas on a little challenge with a classical cassegrain telescope. The telescope itself came out of a Skylark rocket, so its a piece of history that would be great to get into use. The story is that I tried to figure out where the focal plane was before building anything, and I thought I found it quite far out the back of the tube. Of course I was expecting to find focus somewhere behind the primary. Turns out, I was quite wrong, and now the mirrors are recoated, I managed to find the focus by taping a an ASI224 to a metal ruler and inserting it inside the tube. It comes to focus very nicely 10 inches inside the tube, way in front of the primary. A diagram is attached. This is a little inconvenient for amateur use. It also means I can't use a traditional focuser, or indeed an eyepiece. What I need to do is bring the focus about 20inches back, so it falls outside the back of the tube, like a normal cassegrain. The only real idea I have is to move the secondary closer to the primary. Is it as simple as moving the secondary 10 inches forward, pushes the focus 20 inches back, as you cut out 10 inches on the forward and return light path? What other impact would moving the secondary closer to the primary have? I guess it would increase the focal ratio? Before I go trying to engineer this, do folks think it would work? Any other good ideas on how to achieve moving the focal plane back? Any help gratefully received. Many Thanks, Dan

That's great. Thanks.

Hah! I know Eastleigh... actually Bishopstoke, but I put Eastleigh, since no one has ever head of Bishopstoke Light pollution south is a real problem. The airport is floodlit all night every night, and the uni sports fields don't help. I am looking at getting out to the new forest, or Old Winchester Hill on the South Downs. I really should do it one day! This winter I definitely will. Probably.

I also had a 12'' LX200 for a while which I had a crack at imaging with. Everyone's points above are very valid. Make sure you have a really good heavy wedge. The single biggest change I made was changing from one of the Meade cast wedges, to some fat aluminium plate wedge someone had homebuilt. Astrophotography when from impossible to quite possible. Collimation was the other pest. I found the old quip... SCT users spend half their time collimating, and the other half wondering if the collimation is OK... applied quite accurately to me. I was forever faffing with collimation. Cool down time is also loads longer than you might think. Even having mine in an obsy it could take 90 mins to cool once opened to the air, with the first 60 giving complete mush. I think overall the LX200 was a very capable telescope. I always thought it had more capability than I could extract from it with my skills and patience. Mostly, despite some frustrations, it was a really fun scope to have and use. Tinkering, improving, figuring out how to get the best out of what we have, is (for me a least) a good portion of the fun. I absolutely accept an LX200 isn't the most efficient way to go imaging. There is something fun about long FL imaging though. Have a go with it. See if you like it!

A great motivational read. Was all this from your back garden? I see you are Southampton. Is light pollution OK for you, allowing M31 to punch through well?

The one I got had been previously upgraded with an awr kit. It was a very good job done. I was looking for something a bit easier to integrate with a pc for imaging and had prior experience with onstep, so I took off the awr drives and replaced them with an onstep system. If you are a bit handy onstep could be for you, and the whole thing can be done for a couple of hundred quid. Let me see know if your interested in onstep and I can surely help you out.

I posted my message in the wrong thread, but its worked out somehow. The base looks exactly like that one, and yes, the axes cannot be locked. They can be made quite stiff though, as mine has 3 large nylon tipped screws on each axis that can be tightened or loosened to set the amount of force required to move the axis. They are under the black painted cowling on mine, so could be worth digging into your one and seeing if you have them.

An unusual one.... its a Rob Miller prototype from the end of the 80's modified with Onstep drive control. Here it is happily holding a 14inch classical cassegrain, with 25kg of counterweights. A lot more info on this and other mounts in this thread:

An unusual one.... its a Rob Miller prototype from the end of the 80's modified with Onstep drive control. Here it is happily holding a 14inch classical cassegrain, with 25kg of counterweights. A lot more info on this and other mounts in this thread:

And here it is mounted. With 25kg of counterweights. Will check I can focus on something, and assuming that goes ok, then I need to fit a focuser and recoat those mirrors and its done.

Had a really interesting discussion in this thread about an old telescope from the 1970's which was mounted in a Skylark rocket section. Ended up messaging Robin Brand who wrote a book on the subject of the Skylark Sounding Rocket and gives talks. Details are all in the thread linked above.

For completeness: I messaged Robin Brand, who wrote the book on Skylark systems... his reply was very thorough and shown below. I think we can consider this case closed. From no idea, I now have a very clear idea of what it is and I can move onto the challenge of mounting it. It isn't too heavy for a 14''. Which still means its really heavy, so some nerves here that I'll actually mount it properly. I can take off the main visual back which is a really heavy piece of metal, and replace with a polycarbonate one, which'll do until such time I get a nice aluminium 5 spoke thing machined one day. This will save 10kgs or so. And mount a losmandy d-plate on with 4 M8 bolts and it should be good to go. Once I've got it mounted and tested it'll focus etc, then the mirrors really need a recoat... but no screaming hurry for that. Robins Reply: Regarding your Skylark SL1113 query, I've now had a chance to check my records, and the short answer is that it does appear to be a prototype experiment from Culham that never flew, and indeed that I have not come across before, so it really is most interesting. In more detail, as the correspondence in your thread has correctly identified from various sources, there was an SL1112 launched in November 1975, and also an SL1114, SL1115 and SL1115A launched in 1976 and 1977, (see p.603 attached), so it must be of that era. The way the system worked, was that batches of SLxxxx numbers were issued and assigned, but vehicles/experiments could be launched out of numerical order if one was delayed during development, or perhaps not launched at all, if there were major technical or funding issues, as appears to have been the case with SL1113. Perhaps it was based on that of SL1004 (pp. 449-451 attached). The difficulty here is that if an experiment failed to work, or even worse was never launched, then no scientific paper or (if no launch) trials documentation would result, i.e. nothing would be formally released, so info is difficult to find. However "Culham" (the UK Atomic Energy Authority’s Culham Laboratory in Oxfordshire) were one of the largest users of Skylark, as the Sun was a useful fusion source to study, and my book includes some 60 references to them. (In particular, page 245 of my book refers.) So what appears to have happened here is that the development of the payload for SL1113 started, and was mounted into left-over non-flight body segments from SL1111 and SL972. (The designation "ARU Stellar) on one of the fine photos you posted must indeed refer to the 'Astrophysics Research Unit" of Culham - my book page 610 attached tries to untangle their complicated history.) Telescopes - it was surprising what could be accommodated in the 17.5" vehicle diameter, see page 268 attached. (And in the pre-digital age, the inherent sounding rocket ability to return photographic film to Earth was a big advantage over orbiting satellites, the ability which otherwise was only really practical with manned spaceflights.) And talking of the Skylark body sections, these were made of 'magalloy', a lightweight structural magnesium alloy, which 'weathers' as your example. (These formed the basis of a useful 'Lego' type construction system, in which sections could be clamped together to build bespoke launch vehicles.) Anyway, I've gone on long enough, and hope the above is of some help and interest. My book I refer to is the standard work on Skylark "a readable work of reference" - (http://www.new-forest-electronics.co.uk/skylark-book.htm ), which includes lots on the pioneering UV & X-ray astronomical experiments flown. And would your group be interested in a talk on the more general history of Skylark? - I do have a presentation which is astronomically oriented & which I have given to several societies, which can be in person if within reasonable distance, or alternatively online. (http://www.new-forest-electronics.co.uk/skylark%20events.htm)

I did contact Robin at newforestelectronics. He said form the pictures it was certainly a skylark section. He will check his records when he gets back from a break. I also noticed last night that one of the bits says SL972. That one did fly with an Xray astro experiment. The telescope I have wouldn't be much use for Xray. I guess they may have reused parts? Or perhaps more likely I have acquired an odd assortment of Skylark bits! The sticker says SL1113, the white pen mark near the sticker says SL 1111 and the most purposeful mark says SL 972. Fascinating whatever it ends us being.

Maybe not though! http://www.new-forest-electronics.co.uk/skylark mission index.htm Again SL 1113 is missing. SL 1115 is listed twice, the second one with an A on. Wonder what happened to SL 1113

I'm fairly convinced that is what it is. http://www.sat-net.com/serra/skylar_e.htm This shows the Skylark launches. SL 1111, SL 1112, SL 1114 are all there in the 1970's. SL 1113 isn't listed. Just noticed in that page linked above.... SL 1115 is listed twice. Reckon the 12th May 1976 should really read SL 1113! Thanks for that link Mark. It looks very much like that indeed.

Found this: https://www.nature.com/articles/physci246037a0 Note the Skylark Rocket payload used in that article was SL 1111. The sticker at the bottom of the first image says SL 1113, so it looks like it was a payload destined for the Skylark rocket program. This page: https://www.hep.ucl.ac.uk/history/Fox3.shtml reference 224 talks about the UV astro group collaborating with Culham using a Skylark to launch a cassegrain telescope for UV spectroscopy. Wonder if SL 1113 ever flew?

Some great leads there. Thank you. The tube material appears to be aluminium to me, with a textured surface, or thick textured paint. The IR balloon idea is interesting. Apparently this has been tried a few times over the years by different folks. You're right though... how on earth do you point it where you want to?

I have a habit of buying quirky stuff. This time I got the most extraordinary telescope I have ever seen. I don't know a lot about it. It says Culham Laboratories on the tube, and 'ARU Stellar'. It has lots of clamp rings that say 'Flight' or 'Non-Flight'. It is a 14'' primary, folded optical design, something line a classical Cassegrain or Dall Kirkham. Wonder if anyone here can identify it? The first image shows the cased tube. The second picture shows down the telescope. Mirrors need a clean, but are in decent condition otherwise. Picture 3 shows up its backside. It has a pretty large central obstruction. The fourth picture shows its 'focusser'. Rather its a dovetail onto which instruments were mounted by the look of it. A fairly complicated little exit port there. The fifth image is the telescope mounted on top of one of its case sections. I really like restoring and giving old scopes a second life. But this is something else. The good news is that with all the metal tubing stripped away the scope itself is not too heavy (so I can probably mount it and have a hope of tracking something). I am not sure about the plan beyond that. I suspect I'll have to get rid of all the casing, since it isn't needed, and its huge. Then make a custom backplate, or adapt what is there to get a more standard amateur fitting, and a dovetail rail on it for mounting. All of these options seem possible. Bit concerned about adapting something with such a 'no expense spared' look to it with my basic metal work skills, but I'd love to give it a second life, and no point having it sat in a garage for any more decades. (reckon its from the 1980's). Any ideas on what it is, why its was made, or what to do with it are welcomed. Think you'll agree, this one is no ordinary telescope! Dan

collimation.

For the 12T - 48T Dec the length is 147 For the 20T - 48T RA the length is 154mm But it is often hard to find the exact belt length you need, so some fettling is often required. The calculations are form the link I posted earlier. Dan

Oh, you can measure the edge of the motor there to the edge of the shaft pretty accurately. Then you know the motor width and the shaft diameter, so you can calculate the centres. Probably how it should be done. I'd just get a caliper and measure roughly centre to centre. To be fair I have had to rebuy the odd belt... so now I usually go one tooth over and space, rather than one tooth under and find its too tight

This one details the build: It is also in more gory detail on the Onstep Showcase page. You don't need to be really precise, as I found it really hard to get exactly the right length belt. Usually a little spacer is required to get the right tension. I have used washers around the mount screws before, or had a bracket I could slide up and down. You can also use belt tensioning pulleys, but that is a bit fancy pants!

Hi Daz, Belt length calculator here: https://www.technobotsonline.com/timing-pulley-distance-between-centres-calculator.html Assuming you are using GT2 belts, which work well, ebay is a place to get the pulleys and belts. They are pretty cheap, just take care its a UK supplier if you don't want the long lead time. Printing stepper mounts is a good effort. I used MaxESP for all my builds. It is probably a perverse choice, as its is one of the trickier ones, by all accounts but it was the more powerful option when I started. There is the FYSTEC option now, which looks really simple to implement, but hardware is pricey in the UK. I also got a lot of help with my first build, but it is a good helpful community, so got there in the end. Build 2 was a doddle vs build 1. Dan

I have, multiple times! First was converting an LX200 classic to Onstep. Second was replacing and AWR drive system on an old mount. How's your build going?

Thanks for your comments. I think deforking is pretty much a one way operation. Very hard to put back on well aligned, from what I understand. And yes, I can't justify the scope just sitting there doing nothing. Not sure whether the mount would take a 17kg OTA. Probably be OK for visual. It isn't a standard mount, but it is rather heavy and large, so it'd be interesting to see! Thanks for the tip on the screws! I also learnt that a while back, but may well have relearned it this time too! And yes, it might be a hard sell to move on such a heavily modded item. I think its all to the good, Meade lx200 12'' with modern electronics, but people tend to prefer original examples I think. I do think it'd sell for enough for me to be able to replace it with a C9.25 OTA though. Not an Edge HD one mind! Today I am leaning towards the defork. It would be hard to get another 12'' SCT sorted if it turned out I missed it! Appreciate the inputs, Dan