New Project.

[ZeroID]

Just acquired a: (from the email)

Nankivel 8inch f/8 newtonian mirror set - new unused. Other Nankivell elliptical flats and zerodur 1/20 wave flats.

The best way to judge the Nankivell mirrors are to compare them to a modern equivalent say
http://www.rfroyce.com/stand_mirrors.htm (http://www.rfroyce.com/stand_mirrors.htm)

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 :P 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.

[ZeroID]

http://en.wikipedia.org/wiki/Nankivell_Observatory

OK, so found out who made it ....
Interesting ...

I think I just purchased a piece of history

Garry Nankivell, who made the optics for the 1 meter telescope at Mount John

http://adsabs.harvard.edu/abs/2002ExA....13...59H

[Tinderboxsky]

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.

Steve

[ZeroID]

12" f8 .... you're gonna need stilts. :rolleyes:


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.

[Rac]

New projects are the best!

[ZeroID]

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.

[ZeroID]

Pics of the mirror and diag on it's way. Done some dimensional designs and rehashed some ideas.

[ZeroID]

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.

[Merlin66]

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 brock]

"Serrurier Truss using a hex box centre cage with three open sides and diaphragm bracing at each end."

Looks like a Serrurier Truss description to me.

Dave

[Merlin66]

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.

[dave brock]

Oh ok, I stand corrected. :thanx:

Dave

[dave brock]

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.

Dave

[sopticals]

Hi Dave,

how did they test out?:question:

Stephen

[dave brock]

Hi Stephen.
With risk of being blasphemous I'll just say if I was working them I wouldn't call them finished.

Dave

[ZeroID]

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 .... :confused2:

Anyway I've cut the rings and spacers for the UTA. The workshop is full of router sawdust.

[dave brock]

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".

Dave

[ZeroID]

No problem Dave, now I'm wishing I had a tester :lol:.

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. :thumbsup:

[ZeroID]

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. :question:

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. :thumbsup:

[ZeroID]

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.

[ariefm71]

Nice looking mirror... At 64" FL, it may be at the maximum limit of your eq6. Should be great as a travel dob. Keep us updated!

Arief

[ZeroID]

For those who are interested I tried a simple Ronchi test on the mirror tonight. Just as well I have a long workbench in the garage cos I was twiddling around at 3.2 meters. I don't have a tester as such but taped a printed ronchi screen (200 lpi from Stellafane) over a small led torch ( don't laugh, it works ! ) and in the darkened garage had a look. Looks to be a very classic long FL Parabola. Central bulge and curves with a wee turn out near the edges. No deviations I could see. Mirror seems good.

>Arief : Nope, should be good on the EQ6 for weight. Construction is very lightweight so far. Using a 6 strut design (3 pairs) rather than 8 and UTA is in 12mm ply rings. My EQ6 can handle the 10" f5 no problem. Weighs about 18kg all up. This should be lighter although longer. Parking it on the mount might be more of an issue with roof height and distance to the Ob walls. OTA total length should be just over 1.5 meters.
I'll get some pix done tomorrow.

[ZeroID]

UTA pic as promised. Very lightweight. Note the nice clean working area :D. The 6 struts are 2 alum 10mm tubes plus 4 alum split extrusions with an extruded side plate seen in the second pic. The Focusser plate will be attached there and a light shield on the opposite side. Dowels in the tube and wall fitting plugs in the split extrusions hold the screws.

[ZeroID]

Funny how ideas come to you if you ponder long enough. The spider design has been bothering me. I like Rolfs wire model but wasn't comfortable with it's mechanics, seemed slightly complex. I didn't want to go with another 4 vane version as in my f5 10". Hunted around on www and found some Guitar machine heads in black. Then thought about how guitars guide their strings over a metal or plastic bar at each end. Which led to thinking about mounting the Machine heads through the UTA upper and lower rings with the capstan above and below each respectively and guiding the wire (.23mm steel E String ) over the outer edge with a metal guide. It extends the wires to the max angle with no chance of slipping off the capstan.
I like the idea so much I'm ordering 3 sets ( 6 heads in each set = 18 ) so I can modify the 10" UTA as well. I need 8 for each UTA and they're only $10 a set. E Strings are $3 for 5.
Watch here for updates :thumbsup:

I just LOVE DIY problems.. :D

[ZeroID]

Cloudy weekend, lots done. Got the 12mm ply, build the centre cage. Drew up a cardboard template first so I could draw them out identical. Marked up the ply and routed the centre hole and then trimmed the Hex's out. Cut 3 pieces of 20mm finished timber and squared and sanded them to exactly equal length. The cage is the reference point for all other measurements so needs to be as square and parallel as possible. Checked assembly accuracy then glued and triple screwed every joint. Checked after completion and it came out within .25 of a mm for parallel between the two hex faces. Phew !
The dovetail will mount off one of the three side plates, a guide scope off one of the other two sides.
The round disk assembly on the last photo is a tentative idea for a back plate for the mirror cell, still cogitating on that and ideas for the truss tubes mounting hardware.
Also picked up some varnish for all the timber work and the three bolts and wingnuts for the mirror cell.
Machine heads and E strings are ordered.

[ZeroID]

It's been a wet and wild weekend, can you tell ? More progress with the centre cage. First a trip to Bunnings for a few bits then made up the brackets for the truss struts to attach to. All cut and filed to the same length then set up a jig on the drill press to drill the holes all accurately. I have worked out a neat and tidy attachment method you'll see later. Drill presses are very useful.


Then started the mirror cell. Basic design now sorted. Still a lot of weight to be removed from all the ply disks involved but again minimal hardware and complexity.

[ZeroID]

Update & Piccie Time, quite a bit been done. Centre cage finished, Mirror cell done with my mini 6 point cell design and UTA waiting for Machine heads to arrive. Also a look at a simple adjustable drilling jig for when you have maintain dimensions across componentry.

[ZeroID]

Mirror Cell assembled except for side retainers. I'll fit those when I place the mirror on so I can set them for minimum gap. Velcro mirror pads are in place now. I strip the white backing off the top and lower the mirror onto them and that's it.
Side on shot shows the rubber 'tyres' that are the adjustment springs for the cell. Entire cell is only just over 5.2 cm deep, very low.

[dave brock]

You don't have a pad at each end of the three bars? If not it's not really a six point cell.

Dave

[ZeroID]

Been busy again.
Built and assembled the LTA and trusses. Again the critical factor is accuracy so the distance between the bolt holes on the trusses has to be identical, 380mm in this case. The wooden insert is to give the alum tube end support and held the shape under compression of the screws. Finished up weighing 2.9 kg and the back plane for the mirror cell is parallel within 1mm of the front element of the centre cage.

Guitar machine heads and the strings have still not arrived yet so UTA was untouched for now.
Once it is all assembled it will all come apart again and all shiny metallic surfaces will be sprayed black matte. Was looking for a protective cap and light shield for the mirror once installed and I think it may end up being a 230mm cake oven tin. Should sit down over the mirror onto the brackets nicely. We'll see.

Dave > If I use a blob of silicon at each end then I have a six point cell. I chose to use the Velcro because it is a heck of a lot easier to remove and reposition. I understand what you are getting at but if you look at the alum bar as a lever then the ends are the levelling points as it rocks to evenly support the mirror. The other nice thing about the Velcro is it has a minute amount of give vertically and horizontally in the flex of the hook and chain surfaces so minimal stress.

[ZeroID]

Guitar Machine Heads and 'E' strings arrived and it was a wet weekend so workshop time. Other than attaching the mirror and centering the mirror support that is completed. That will let me preset the upper truss lengths so they are last on the build list. I'll grab the dovetail off the 10F5 for now and I have a spare finder bracket.

[Rac]

What method are you using to line up the wires as to not end up with heaps of diffraction spikes?

If its only a visual scope then it may not matter so much.

[ZeroID]

The wires are only .23mm diameter, almost invisible and I will blacken them later. The scope is designed as an astrograph specifically, it is not a visual scope.

[Rac]

They maybe thin but they will not be invisible. You could end up 16 spikes if you're lucky. If each side is not lined up that makes them .46mm and if one side is not parallel to the other you will get two spikes per side.

[ZeroID]

Design and accuracy in build, I've spent quite a lot of time working on this idea ... we'll soon see. This is my third reflector scope build, I seem to get better each time and I am only emulating Skyvikings (Rolf ) work.

[dave brock]

Blackening them will actually increase the diffraction spikes by making the wires slightly thicker.
Very nice build, looking good. :thumbsup:.

Dave

[Rac]

Rolf made a nice little adjustment setup for his wires. Even a recollimation can make the wire add up or be offset.
http://www.rolfolsenastrophotography.com/Equipment/125-inch-Serrurier-Truss/i-Sv5t7q6

All looking very nice btw.

[ZeroID]

Thanks Dave,
Black Marker pen, it will stain the wire surface, virtually no thickening.

Rac > Yes, my last build followed Rolfs model, the 10' F5. This build I've picked up the wire spider ( I may modify the 10" as well, I bought extra Machine Heads and 'E' strings)
If you are referring to his swivelling pivots for the machine heads, yes, I was aware of them. But another comment he made was how stable and rigid the secondary was in the wire spider. It holds collimation and under normal use shows no movement at all. By coming through the UTA rings with the spindles and matching the alignment and wire clear side on the spindles of the machine heads they all align and free float without the need for any more mounting hardware. My UTA is therefore shorter and lighter. Also this is a 6 strut build rather than 8. Saves weight again and aesthetically it just looks better matching with the mirror cell bolts which always bugs me with visual alignment of all the nice hardware. Yeah, I know, a bit OCD .. :P
I may need to adopt his method if I convert the 10" as the build specs are different for the UTA.
Hopefully this weekend I'll get the upper trusses done and assembled and you can see the whole beast. I'm kind of impresssed with how nice it looks and how well it has come together myself. A rather satisfying project. :)

And if this version of the spider doesn't work as expected I can easily build a conventional 4 vane, more fun workshop time. :thumbsup:

[ZeroID]

Another (extremely) wet weekend and OTA is fully trussed. Axially it is about 2mm out of alignment end to end but that is easily sorted. Not bad result I thought. I'll tweak that right first and do a simple collimation with some spare mirrors I've got before I add the secondary. Then it comes apart for blackening all the shiny surfaces, light shields for UTA opposite the focuser and around the primary and the dovetail attached.

[alistairsam]

Looks good Brent,

at some point, you might want to consider using Carbon Fibre Tubes instead of Aluminium even if just for the UTA.
you won't believe the rigidity a broad diameter CF twill tube offers and the weight it reduces and costs around $30. But don't get it from ebay. they're hopeless.
https://flic.kr/p/o6hNnU

Cheers
Alistair

[ZeroID]

Haven't seen any suppliers over here for CF. I actually enjoy the build process of this type of construction, the challenge of doing something a bit different. This one has been a real exercise in design and execution to much more accurate specs than I have achieved in the past. Hopefully, optically it should perform as good as an APO and with a 2" 2 x Barlow be a bit useful on planetary targets using the ZWO ASI 120mc.
Trouble is I didn't figure on how many clouds (and rain) it was going to generate. This lousy weather is predicted to continue till next weekend at least.

[ZeroID]

Wet lacquer drying in the winter shade. Then mirror cell with retainers and the velcroed mount pads. Mirror in place and light shield then the styro lid to keep it safe.

Not shown is the secondary attached to the spider all ready to go. Did a simple collimation and it looks good. Can't do a full 'on-axis' collimation till the silicon sets in the side retainers. Fun twiddling the machine heads to move it round. I centred it first with a ruler.

I've had some eyes raised in the past about the Velcro mirror mount system but I did a simple test with this one. Once the mirror was bedded down I held the sides of it and lifted the whole scope up ! There is about 6 sq inches of Velcro surface ( industrial strength ) and it is rated as being capable of supporting a minimum of 2 lbs per square inch. ( USA supplier ) so between that and the silicon side buttons I feel quite confident with the system.

[glend]

Looks great Brent, makes me want to build a bigger one.

[ZeroID]

First imaging test, no, the clouds HAVEN'T gone away. In fact it is raining cats and dogs. So this is bench mounted in the back of the garage pointing outside through the gaps in the neighbours deck rails at a couple of Norfolk Pines about 4 km away in steady rain. ( It was the only distant target I had in the circumstances ) The 'vignetting' is actually the upper most rail on their deck intruding into the frame.

If you look closely at the top of the leftmost tree ( jpg compression and size of file allowing of course ) you can make out the pine branches and the leaf extensions individually ..

I hereby declare this build a success :P
Now where did I put my cloud sucker upper :rolleyes: ??

[Rac]

Awesome. This weather in the north of NZ has been total crud of late and it's all because of you.

[glend]

Single speed focuser? Was that by choice or what you had on hand? BTW i'd love to see a detail photo of the guitar string arrangement and tensioners. Did you use guitar string keys to control the tension and how are they mounted? Looking at that for my next scope. Looks great, but you will now have cloud and rain for months because of it.;)

[ZeroID]

Hahahahahahahaha... probably true !!! Sorreeeeee !!

GlenD> yeah, the focusser was what I had available from my 10" upgrade ages ago. I'll upgrade if necessary although I think I would go for motorised maybe, another project for DIY ? :P . This thing is quite long and the focusser is going to be a reach.

I'll do you some Guitar Machine Head pix and post them up but nothing to them really. I just drilled holes through the rings and mounted them as per usual fittings would allow. I faced them outwards for three reasons, 1, to maximise the angle to the centre, 2. to stop the string winding off by being pulled over the end and 3. to protect the knobs from bumping as much as possible. Rolf uses a swivelling block to keep them straight but in my case they just come off the spindle to the centre and float clear of the rings. That works for guitars, works for me. Simple and lightweight.

[ZeroID]

Spider details. I had to add a brass spacer under the machine head nut to make it tighten up but other than that all the hardware for it comes in the packet. Wee screw at the back to stop it turning, black washer and nut. Got it all ( 3 sets of 6 ) plus I think 5 packs of 'E' strings for about $40. I have enough hardware to modify the 10" later if I want.
Excuse the garage mess but there is the whole scope as tested.

EDIT: Each 'pair' of machine heads, top and bottom ring are aligned and by using the left\right sets ( 3 of each in each pack ) all the knobs turn the same way to wind off or wind on and the strings also align off the same side so stay parallel and hopefully (within tolerances ) also vertically aligned so minimal diffraction or added thickness. Strings also blackened with permanent marker pen, very little additional thickness added.

[glend]

Thanks Brent appreciate the photos. It is long looking at it on the workbench. Do you know the final weight yet?

[ZeroID]

Hmm, no, actually I don't. Hang on ......

8.6 kg ! half the weight of the 10" ( I just whizzed downstairs with the bathroom scales, thanks for reminding me )
That is slightly better than I'd hoped, 10 kg was my expected result.
Overall it's nearly 1.6 meters long, max width is 350mm. Still to get finder and guide scope attached.
Weather is a bit better tomorrow supposedly, I'll try and do a few more imaging tests under better conditions.

[ZeroID]

Siliconed the secondary in place last night. Hoping for first light over the weekend.
You guys, buy something !! Keep the clouds preoccupied so they don't notice anything ...

[Kunama]

Nice work Brent, maybe I should have started with a small mirror as well.
Looking forward to your First Light Report !!!

[ZeroID]

Well the weather has been EXTREMELY uncooperative this weekend so First Light is delayed. I pulled the dovetail off the 10" and mounted that onto the scope. I have a guide scope idea coming along. Planetaries are all very well but I want more from this than just that. Hopefully later in the week the weather is looking a bit more promising.

[ZeroID]

It's up on the EQ6 finally and did some photo tests and a realignment of the mirrors. She is a bit tetchy to fiddle with, requires very little tweaking to make a big movement. Finally got it right and took some pix with the SONY. It has a focus aid highlighter on the back screen. It's looking good so far. Two shots of houses, the same house not centred in the second shot but with a 2 x Barlow. Distance is about 3.5 km. The crane boom shot is about 2 km away.

Sorry, no 'First Light' yet, weather is NOT cooperating. No sharpening done on any pic.

[ZeroID]

First light for the RN 8F8 scope. Downright freezing out there (4* !!).
This is a single frame ISO 6400 15 secs in the SONY SLT A77v DSLR unguided and basic processing. LP is high so red shifted downa lot and noisy at ISO 6400 so I ran Noiseware over it to calm it down a bit. No darks, no flats no stacking.

I have some more of K Cru and another small cluster in Carina but I need to play with them a bit. I should be able to stack a group of frames on Eta C later but it's way past my bedtime. Just happy that the field looks quite flat.