telescope build
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Re: telescope build
Another thought would be to check in a store which sells water heaters and the like (some place like Lowe's). They sometimes have a rather large diameter "pan". They typically have a hole cut in the side but you may simply be able to tape over the hole and use it for that purpose - but they may not be as deep as you might want.
Worst case you make a wooden frame and line it with plastic sheeting.
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Re: telescope build
Perhaps one of these might just be on the edge of roughly large enough?
https://www.agrisupply.com/sheep-tank-2 ... /p/110052/
* Celestron C6 SCT on a Twilight 1 Alt-Az mount
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- yobbo89
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Re: telescope build
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .
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Re: telescope build
Each mirror (24") displaced 15,150 ml water and they each weigh in at 90 lbs. So I calculate the density at 2.69 gr/cc which means they are most certainly Al.
Now I need to do the foucault test to see about the curve and also start researching how to grind and/or polish Al.
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Re: telescope build
I'm going to start reading about dobsonian designs.
Thanks so much all you searchers for sharing your knowledge and experience. What a great thing the internet can be!
- DeanD
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Re: telescope build
I hope you don't plan to hike up the mountain with it!bobsorenson wrote: ↑Thu Nov 07, 2019 9:14 pm Is 90 lbs a reasonable weight for a mirror? I hoped to be able to go up the mountain here (9500 ') and set up.
I'm going to start reading about dobsonian designs.
Thanks so much all you searchers for sharing your knowledge and experience. What a great thing the internet can be!
That is quite heavy: in my mind I was thinking that aluminium is light-weight, but 1cc of glass weighs around 1.6g: a lot less! An equivalent glass blank would weigh 55 lbs...
This will impact on your mirror-cell design in order to avoid flexure. There are a lot of ideas out there about mirror cells and supports to try to minimise flexure, but they all relate to glass mirrors. I would assume that a multi-point support with 9 points spread over 3 triangles should be OK, but I'll leave that to the experts.
At least you wont have to worry about adding counter-weights to offset a heavy secondary cage!
Have fun, and all the best.
Dean
Binos: Steiner Wildlife XP 10x26, Swarovski 8x30 Habicht, Zeiss SFL 8x40, Vanguard Endeavour 10.5x45, Fuji FMTR-SX 10x50, Tak 22x60, Orion Resolux 15x70
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Re: telescope build
It is a question of whether something similar already exists for aluminum.
Eps: 4mm Ramsden, 6mm Huygenian, 12.5mm Huygenian, 20mm Huygenian, 4mm Plossl, 10mm Plossl, 20mm Plossl, Barlow 2x, Barlow 3x, Barlow 5x, Solomark LP Filter, Dark Green Moon Filter.
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Re: telescope build
I have been looking for info from people who have experience grinding/polishing Al mirrors without sucess so far, but I will continue.
Lots and lots of knowledge available about glass etc but no hands on experience with metal mirrors. Same situation with design and build of a 24"
Not complaining here of course, just searching for know how and trying to make a sensible plan.
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Re: telescope build
thanks to all for the input and information. I will likely use them for some solar concentrator project.
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- Marcelo F.
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Re: telescope build
Sooo....bobsorenson wrote: ↑Sat Nov 09, 2019 6:34 am after corresponding with a person who has years of experience making mirrors for the military, I've come to the conclusion that the mirrors I have will not be suitable for an optical telescope. They were probably made for lasers and cannot be made to be accurate enough for visible light.
thanks to all for the input and information. I will likely use them for some solar concentrator project.
Can we still build a death star?
Eps: 4mm Ramsden, 6mm Huygenian, 12.5mm Huygenian, 20mm Huygenian, 4mm Plossl, 10mm Plossl, 20mm Plossl, Barlow 2x, Barlow 3x, Barlow 5x, Solomark LP Filter, Dark Green Moon Filter.
Binoculars: Bresser National Geographic 7x50, Omegon Nightstar 20x80
Camera: none
Messier: 7/110
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Re: telescope build
I am in hopes that the original figure of the mirrors is somewhat intact and that if I am careful, I may be able to avoid significant refiguring. This approach will require testing of the mirror concurrent with the work on the surface, so I will be building a Foucault/Ronchi unit to enable progress in the right direction.
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Re: telescope build
This is great news. Perhaps you could start another thread over at The DIY Corner --
Cheers,
JT
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
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Re: telescope build
I'll be spending a few days getting testing equipment ready and procuring materials for polishing etc. Plus a test stand for an eighty lb mirror!
When I get closer I'll start posting pics and making reports.
- SkyHiker
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Re: telescope build
If you look at Mike Clements' 70" mirror that was also meant to be used in space, his focal length is about 60' so he built a flat secondary about half the size to reflect it back to the base because a traditional Newt would have it 60' in the air. Do you plan on doing the same?
The mirror is awfully thin compared to glass mirrors, if it may behave well in space it may not, on Earth because gravity will flex it.
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Re: telescope build
The mirrors were for ground based lasers I think, not space. Part of the Star Wars program. The story I heard when I bought them is that they were bolted to a rather large control unit that was too heavy to lift with a forklift, so had to be taken apart and parted out.
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Re: telescope build
I'm making some progress on one of the mirrors so I thought I'd make a report and post a pic.
I've got the beast on a turnable spindle and have started working the surface. First I constructed a wedge shaped tool to lap/polish with. This is made of hard maple and laminated with polyproplene. Since the mirror has its figure intact, I shaped the surface of the tool to the curve by rubbing on sandpaper taped to the mirror down to 1500 grit.
So far I have used short radial strokes to equalize abrasion and lubricated with water and dish soap, down to 600 grit. There is some pitting and I am deciding whether to grind it out or not.
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Re: telescope build
See Far Sticks: Elita 103/1575, AOM FLT 105/1000, Bresser 127/1200 BV, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS 100/1000, Vixen SD115s/885
EQ: TAL MT-1, Vixen SXP, SXP2, AXJ, AXD
Az/Alt: AYO Digi II, Stellarvue M2C, Argo Navis encoders on both
Tripods: Berlebach Planet (2), Uni 28 Astro, Report 372, TAL factory maple, Vixen ASG-CB90, Vixen AXD-TR102
Diagonals: Astro-Physics, Baader Amici, Baader Herschel, iStar Blue, Stellarvue DX, Tak prism, TAL, Vixen
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Re: telescope build
The accuracy you need, say 1/10 lambda, is about 1/20 of a micron. How much deflection will you get by the uneven pressure of your pie shaped tool?
I would make a mirror testing tool and become proficient at using it and use it a lot, that should tell you how well your progress is if this works at all. Most people start with a 6" mirror for practice before they move on to anything else, and many have failed with thin mirrors.
- OzEclipse
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Re: telescope build
I would suggest to give the surface a very gentle polish to remove oxidisation, this itself may change the figure. I would use cotton wool and a light polishing compound, nothing hard that will refigure it. See what you've got before you embark on a refiguring project.
If you can get hold of, or make an artificial star. Set up a star test. A ball bearing in the sun up the street will do it.
I'm sure there are plenty of instructions / videos on line for interpreting a star test.
Then consider your next move. If the figure is not great, you might still be able to use it, literally as a light bucket.....no high mag resolution limit views of planets or double stars but amazing lower power views of galaxies and faint nebulae. I'm not saying that it's as good as an accurately figured mirror, but if you've already got the mirror, make a cheap and easy
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
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