Part of a deceased estate being liquidated I believe. Comes with some Dob components as well but I want to build a longer focal length astrograph. Should have minimal coma and a deeper focal point. If it compares well with a modern Royce hopefully with a Barlow 2 or 3 should give me a planet killer.
Sounds like a fun project I needed something to build in the workshop when the clouds are being uncooperative and hanging around. I feel another version of the Serrurier truss coming on.
It's a bit long for my other project, a travelling 6' or 8" which packs down. Might find a mirror set for that one day.
And scored a Shorty 2 x Barlow from elsewhere as well. Needed that.
Very interesting. I like seeing earlier good optics being to a modern use. Shall watch your project unfold.
I acquired gratis from the CSIRO an early 80's Optical Works London 12" f8 mirror in top condition. Have worked out my plans but have yet to start. Just hesitating over the length and height of the eyepiece.
Yes, been reading up on Garry Nankivell, died in 2002 but he was obviously well regarded internationally. Links to NASA, the big Uni's and had his hand in some serious astro projects. I better do something good to justify this one. I got the set for less than a std 8" GSO mirror.
Tentative design concept:
Serrurier Truss using a hex box centre cage with three open sides and diaphragm bracing at each end. Some internal bracing for dovetail.
Trefoil mirror cell base and 6 struts each for mirror cell and UTA. ( the 10" is 8 struts ).
UTA is probably a two ring possibly wire braced secondary ( a la SkyViking ). Still pondering on that bit. Some Dob hardware is coming with it, spider ?
Struts will finish with no angle brackets, I'll use embedded threaded rod at each end and holes in the trefoil and lower UTA ring with nuts and washers.
Low focusser height, this is for imaging only. Zero intrusion of focusser tube into light path
Therefore minimal weight and extremely rigid. Accuracy in build will be paramount as there will be almost no adjustment at strut ends.
The 'Russell/Nankivell 8F8' project is officially launched.
Comments\ideas welcomed.
The mirror left Dunedin Friday 2pm by courier. Monday, Tuesday maybe?
I haven't quite settled on a design specific, it will depend on what I can find in the workshop to some extent. The cage is the critical element, everything hangs off that but next step is to buy some 17mm ply and start cutting rings and hexes.
Brent et al,
Can we agree on a "truss tube design" rather than a "Serrurier Truss" design???
Mark Serrurier's design was a specific truss design where the top and bottom truss were balanced to give zero rotation or deflection between the secondary and the primary mirror.....
Dave,
The key elements of the Serrurier design is that the truss sections below and above the central "box" are designed to give the same end point deflection and the attachment points act as "pin joints" to allow rotation to maintain parallel alignment between the top and bottom rings.
If the truss design doesn't have these features then it's not a Serrurier truss design.
Hi Brent.
No doubt when you get the mirror one of the first things you'll do is put it on yor tester?
If so I'd be keen to hear your thoughts. I have a Nankivell 8" mirror and have tested a 6" in the past.
Hi Brent.
No doubt when you get the mirror one of the first things you'll do is put it on yor tester?
If so I'd be keen to hear your thoughts. I have a Nankivell 8" mirror and have tested a 6" in the past.
Rolf (SkyViking) designates his design as a Serrurier, I am working on the same principles. centrally balanced so any deflection in any direction is self cancelling. I'll stick with my naming because that is what I am attempting to achieve.
Tester ? what tester ? Based on Garry's reputation and the description I was given of the mirror by the University of Dunedin who have held it I'm expecting the mirror to be pretty damn good.
Garry Nankivell designed and built the lenses for the 1 meter scope at Mt John in Tekapo. He also designed and finished the big multi segmented mirror for SALT in South Africa.
I guess I'll find out when it arrives. Maybe I should build some sort of tester although I confess I didn't expect to be building any 'special' scopes except using commercial mirrors.
Now you've got me worried ....
Anyway I've cut the rings and spacers for the UTA. The workshop is full of router sawdust.
Ahh sorry Brent, I was getting you and Rac (Raymond) mixed up. He's the one with the tester.
I knew Gary Nankivell. He worked at IRL (now Kiwistar Optics of Callaghan Innovation).
I'm sure you'll be very happy with the 8".
I've been researching Garry having 'found' him and his work. Been quite an interesting story although most of it is very clinical and academic, not much personal stuff.
I'm making the project a bit of a salute to him, I hope I can justify the whole thing by creating a nice OTA. I've recut one of the UTA rings already because I wasn't happy with how the first attempt came out. I normally build for function and ignore asthetics mostly but this time it needs to look as good as it works ..... assuming it works good of course !!
I enjoy my workshop time so no hurry for it all to happen. I might even investigate making a tester of some description. I have enough optics bits floating around. Could be fun. Off to investigate.
Mirror is here, extremely well packed in it's own original box. It's a weighty beast, 2.49 kg.
Details are 1605mm (63.17") fl, 204mm dia, 35mm thick.
Mirror surface and coating appears to be perfect as is the 40mm secondary. From the back of the mirror I would assume 70772 might mean 7 July 1972. Signed by Garry Nankivell, no doubting it's providence.
Now I have a weight to work with we can get down to balance and strut lengths.
Won't be much more happening for the next two weeks though. We're off up North chasing rally cars Friday 17th to Monday 20th for the Asia Pacific Rally Championship based in Whangarei. I'll be running two cameras on a bar, one for stills and the other video.
UTA rings are routed and UTA frame assembled. It's a lightweight design, just over 550 gms. I have a 2" focusser available. I have designed a lightweight mirror cell. The mirror is 37mm thick and weighs 2.45 kg ! So I am not too worried about complex support structures, I don't think it will move regardless. I just need a three point cell with good support security so it doesn't fall out.
Still require ply for the centre cage, this weekend to source and build then it's balance time to get strut lengths sorted.
I'll post some pix up shortly.
The secondary spider is my biggest concern. A 'Rolf' special with guitar machine heads and wires is preferred but I need to source the machine heads. I may build a simple 4 vane temporarily while I get it all going.
I needed something to build in the workshop when the clouds are being uncooperative and hanging around. I feel another version of the Serrurier truss coming on.
.
