Introducing my new Planetary Imaging telescope, “FRED”.
Let me say from the outset that I acknowledge the pioneering work that Anthony Wesley has done regarding the use of very thin aluminium telescope tubes and particularly his ground breaking new design for a Newtonian Reflector secondary mirror spider and mount.
“FRED” is named in honor of Fred Watson, a great science communicator and all round good bloke.
Many years ago, when I was still working on the Broken Hill Mines, I was asked to put on an astronomers breakfast at my observatory for a visiting group of astronomers that had come to the outback for National Science Week. This was my first introduction to the talents of such great science communicators as Fred Watson & David Malin. In Later years after I had finished work on the Mines, when I launched myself into Post Grad studies in astronomy with Swinburne University both Fred and David were very supportive.
“FRED” is sort of a close country cousin of Anthony’s new scope “NEMESIS”.
Felicitously, Resplendent, Exemplary, Designed, Telescope.
But then David, who thought Fred was far too common a name for a telescope suggested the following.
Delightful, Astro, Visual, Imaging, Device.
“FRED” started out on the drawing board following Anthony’s visit back in June 2010. I was just so struck by the difference in the live feed between his Nemesis with its custom optics and my trusty 17yr old Meade production optics. At that stage Nemesis had a Royce 14.5 inch primary with a 1/30th wavelength Antares secondary, all in a very light two piece aluminium tube made by Gary Mitchell in Sydney. We both had the same imaging setup and F/L but, comparing the live feed it looked like Nemesis was a 16” and my scope the 14.5”.
Using the ray trace program Newt, which Bird introduced me to, “FRED”, started to take shape, at least as a ray trace drawing on my computer. I settled on the same size primary as my old Meade, 16” F4.5 but with a 3.5” secondary that would focus my imaging train as close as possible to the scope tube.
I contacted Mark Suchting and the order was placed for my mirror blank from his American supplier 16/08/2010.
I also ordered a 3.5” 1/30th wavelength secondary from Antares Optics 19/08/2010 and contacted Gary Mitchell to make me a two piece fully baffled aluminium tube 30/08/2010.
I planned to use the 27 point primary mirror cell that I built for my original 16” in the new tube. The secondary mirror mount is based on Anthony’s most excellent design. I think that the “Wesley” secondary mirror spider & mount is probably one of the most insightful developments that has been made to improve the performance of the Newtonian telescope design in decades. The secondary mount and spider vanes become one fixed unit. The vanes pass through cut outs in the tube and slots that are in a very heavy aluminium ring that sits on Teflon strips on the outer surface of the tube. The veins are held in position with tension from compression springs. The secondary is adjusted by rotating the aluminium mounting ring and by sliding the vanes longitudinally within the slots in the mounting ring. As a slight modification to Bird’s design I am working on a different adjusting mechanism that will allow very fine longitudinal adjustments of the spider.
Gary Mitchell was great to deal with and did a very professional job on the tube. The lengths he went to in packing the tube for transport out to Broken Hill were greatly appreciated by me, the tube arriving in pristine condition 26/10/2010. It was much lighter than the Meade cardboard tube, a reduction in overall weight of about 20 kg. As the counterweights on my GEM are at double the length from the pivot point of the mount than is the centre line of the scope tube, I was also able to do away with 1 of my 10 kg counterweights. Thus giving a reduction of 30 kg overall on the mount. The thermal properties of the very thin aluminium tube are excellent and track the changes in ambient very well. I am very confident that there will be no tube currents in this scope generated by the tube itself. My new Antares 1/30th wavelength secondary arrived 06/09/2010.
Fitted a new set of primary mirror mounts that I had made to the new aluminium tube. Very carefully marked out the position for the hole to be cut for my JMI Moto Focus, measured it five times using different methods to calculate the measurement to ensure it would be in the correct position. Very accurately marked out the cut outs in the tube that the spider vanes would pass through and cut them out with my Dremel. I then fitted the Teflon strips either side of these cut outs that would allow for the whole secondary assembly to rotate enough to get the correct rotational position for the secondary mirror.
Again with the Dremel I cut the slots in the external 35mm x 5mm aluminium ring that the vanes passed though to allow for the adjustment in angulation of each vane for collimation of the secondary .
I used stainless steel 300mm rulers for spider vanes ( as Anthony had successfully done) with compression springs to tension the vanes to the mounting ring. I Also turned up seats to both locate the top and bottom of the springs with the lower unit also housing a Teflon bush. I drilled and tapped a 3/16 BSW thread into the side of this lower housing and screwed a long 3/16 thread into this that passed through the angle iron brackets discussed in the following paragraph.
When I ordered the tube from Gary I specified an extra 35mm x 5mm internal reinforcing ring to be fitted inside the tube by me later, as close as possible to the external ring that the secondary mount & spider were fixed to. To have the ability for very fine adjustment in angulation of the spider vanes. I mounted angle iron brackets that were bolted though the very thin skin of the tube wall and also though this much heavier internal reinforcing ring.
To make adjusters that could be readily adjusted by hand for the fine adjustment of the vanes I used standard 3/8 BSW bolts. I cut the thread off of them and drilled & tapped them for 3/16 BSW allowing the 3/8 hexagonal heads to become virtual thumbscrews for fine adjustment.
My new 16” F4.5 primary blank arrived in Sydney 11/11/2010.
November 1st 2010 I fitted my new Antares Optics secondary and my 17yr old Meade 16” F4.5 primary to my new aluminium tube and mounted it on the GEM in my observatory.
I was incredibly relieved to find that all of my eyepieces and PGR Flea3 focused at the heights above the tube wall that I had designed the scope to achieve. Since doing this I feel that there has been an improvement in my imaging results, due to the very high quality secondary and the most excellent thermal qualities of the aluminium tube. As my new primary will be the same, or very close to the same F/L as my original mirror it should just be a matter of changing them over when it is finished.
I look forward to having an official first light with “FRED” on Saturn when he has been fitted with a world class primary from Mark Suchting.
( This write up will be continued as this project develops)
Have attached 3 images of the aluminium tube taken by Gary Mitchell on completion in his Sydney workshop and 4 images on its arrival in Broken Hill. It was exceptionally well packaged, wrapped in layers of foam & cardboard.
Cheers
Trevor
Last edited by Quark; 31-01-2011 at 09:14 PM.
Reason: line spaceings for readability
The unique front end design of Anthony Wesley's with my adaptation to achieve very fine adjustment in angulation of the secondary via moving the spider vanes.
I have used a plastic container with a screw on lid to make a protective enclosure for the secondary
This new scope was designed so that the original 27 point primary mirror cell that I designed and built to replace the Meade 9 point cell would fit the new tube, this also meant that the Peltier cooler that I built for said 27 point cell would also fit the new scope.
The front end of the scope with JMI MotoFocus, 5x Nagler Powermate, Orion manual filter wheel and PGR Flea3 camera.
Note that I turned up my own adapter that screws into the nose of the Flea3 and into the filter wheel, reducing the distance between the CCD chip & filters to the absolute minimum.
Note also that I have my modified 8x50 finder with ToUcam fitted, a normal 8x50 finder and Telrad all within easy reach of the focuser.
Also note the positioning of my Unibrain 800 fire repeater on the tube so that a short and light cable can be used to connect to the Flea3 rather than using the very long and heavy cable supplied by PGR,
My computer hutch with FireCapture running on my laptop.
I use a camera tripod to hold the remote for my JMI Moto Focus.
Last image has FireCapture running for the Flea3 and wxAstrocapture running for my ToUcam which has a very nice red reticle overlay and is very handy when initially aligning on my target planet and if for any reason through the session I accidentally bump the scope I can quickly drive the target back using the ToUcam.
Can't wait to see the Pic's this will generate .... Trevor..! Let me know when you've got some.
Hi there Colin, have been using the scope but with my 17 yr old Meade primary since early November 2010. However "FRED" will not truly be complete until my new primary is installed. Mark Suchting is renowned for the quality of his work and I consider it a privilege to be getting a mirror from him, really dont care how long he takes to finish my mirror. When it is ready you can be assured that it will be a world class mirror, then I expect great things from "FRED".
Now I know why you've been a bit quiet, Trevor. What a lovely piece of work.I hope to return to Fowlers Gap sometime this year and must say hello when I come through, if it is convenient. Would love to see that instrument up nice and close.
Nice project Trevor. Plenty of information and pictures, a great DIY.
Thanks Troy.
Quote:
Originally Posted by erick
Now I know why you've been a bit quiet, Trevor. What a lovely piece of work.I hope to return to Fowlers Gap sometime this year and must say hello when I come through, if it is convenient. Would love to see that instrument up nice and close.
Look forward to your visit Erick, was great to meet you down at Bendigo, I suppose thats a while ago now.
Well, I don't know what all the fuss is about?
I have just spray painted my collapsable captain's spyglass in aluminium paint and use it while wrapped in two sports ice packs for cooling and the results are outstanding!
Even water cooled my Telrad!
Seriously though Trevor, that is one hell of a scope!..............more like something from NASA.
Congratulations!....... and I hope you don't loose too much sleep waiting for Mark's super mirror.
Beautiful work Trev, really stunning. I cant wait to see what you are going to turn out with the new mirror. I can imagine you are very excited. But are you sure there isn't something wrong. That tiny tiny tiny camera attached to the filterwheel couldn't possibly be turning out the great image you are achieving now. It is amazing how small they are making those things these days. How long before it going to be just a chip and an adapter and a lead??? wow
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