I want to make a small reflecting telescope. But I don't want to grind the reflector. It will be tiny, maybe 4" / ~10cm diameter.
Is there a cheapass source for these things?
I'd need a primary and secondary reflector for a 4"x70" telescope. I don't care if it's window glass, neither surface nor temperature stability will have to be very good. It's more a proof of concept and a toy.
I've considered just getting a toy telescope and cannibalizing its mirrors. But I haven't found one cheap enough.
>>954976
Check the cloudynights.com classifieds such things aren't uncommon there, eBay may have something too, plenty of cheap mirrors and such from China.
Though desu grinding such a small mirror, especially at a long focal length, will take very little time as it will be a pretty flat mirror, and there will be little need to parabolize it. Even basic window glass of some thickness would be fine.
>>954976
I got a 4.5" reflector with a secondary for $20 on eBay.
>>955194
New or used?
>>954976
>I want to make a small reflecting telescope. But I don't want to do it right. I want to waste time, money, and effort on a piece of junk.
>>955197
Okay, I see what you mean.
Let me be clear.
I want to spend no more than $50 on a project that will demonstrate Newton's design but will not need to be more useful than cheap binoculars.
And what would doing it right entail in your opinion? Grinding? That's 2 mailorders (materials + aluminizing) and a huge mess with the option of doing it wrong on a precision job that takes a lot of experience.
I need a flashlight, not to rewire my building.
>>954976
go big or go home. there are kits for 12" dobsonian scopes. you buy the optical glass blanks and grind it at home.
or you can go to a glass shop, ask for a circular piece of mirror in whatever shape you want and then use a solvent to remove the paint protecting the silver finish on the back. this gives you a reverse faced mirror.
>>955202
Running around with a 12" telescope, reading the news on the subway over the shoulder of a person 2 cars down, calling friends across town to say "I see you!", lighting a cigarette with the power of the sun...
It's: Telescope-Man
>>955207
the size of a telescope refers to the diameter of its primary optical element.
pic related: a 12"
>>955227
>bragging with your 12" Dobson
Midlife crisis?
Has someone here ever shaped a reflector?
>>954976
>I want to make a small reflecting telescope. But I don't want to grind the reflector. It will be tiny, maybe 4" / ~10cm diameter.
>Is there a cheapass source for these things?
The only thing that cheap newt mirrors are used for is cheap telescopes.
You didn't say where you were but anyway.... Being in the USA, my go-to place for cheap optics is Surplus Shed (online, look it up).
They show a couple 4" mirrors but both are out of stock, and unlikely to be in stock again, as they sell surplus stuff.
You can use any round- or parabolic curve concave mirror you find. There might be something else at Surplus Shed to use.
Your best bet would be to ask on the telescope making forum at CloudyNights.
There are other forums but CloudyNights is the most popular English-language astronomy forum by far.
This is something i want to try, if you pour molten aluminum or some other silvery metal into a centrifuge it will make a parabola. Control the speed of the spin and you can move the focal point. Then let it cool while spinning, polish it, and maybe coat it in glass for that extra shine?
>>955665
You shape the glass, then coat that with aluminium. Large mirrors are made with that spinning method. The problem is cooling them slowly so they don't crack, takes years.
>>954976
thumbnail picture looks like you are doing coke off of a table/mirror
>>954976
Could you rig up a mylar covered pressure drum?
Basically, it's a cylinder of a rigid material, covered at one end by a sheet of mylar, which is extremely reflective. You then hook up a vacuum pump to the drum, and alter the pressure to pull a slight vacuum. If the sheet is perfect and you do everything just right, you can make an effective parabolic mirror.
>>955825
The wrinkles from just the tiny parabola you'd need would already crinkle the sheet enough to completely ruin your image. It would work for focusing light as an energy source, but not for creating an image.
>>955817
He's sticking the marker on the center of the mirror which reflects some white stuff (paper?) that happens to be in the room.
>>955817
>doing coke off of a primary reflector
I will beat you with a tripod
http://www.edmundoptics.com/optics/optical-mirrors/
http://www.skyandtelescope.com/astronomy-equipment/astronomical-equipment-manufacturers-suppliers-and-specialty-dealers/
-hackerspace
If you like telescopes...
https://www.youtube.com/user/DeepSkyVideos/playlists
does anyone know how to grind a parabola into a flat disk?
>>958228
>into
as in "from" or in "towards"?
>>958235
I guess from, i want make one side slightly convex. I want to make a speculum disk into a reflector
>>955254
If you've met hobby astronomers you know they care basically nothing for stuff that isn't lightyears away. So no, this is a midlife control, not a midlife crisis.
https://www.youtube.com/watch?v=z2UnicxC8hs
>>958480
A historic reconstruction?
With glass you slide two pieces across each other using abrasive and water, the movement of that determines the shape. It leaves one side concave and the other convex. Not a trivial task, takes a lot of experience and expertise to correct the optical properties. During production you check the work with a reflective water film. When it's good you polish the surface to a few nanometers by hand and finally have it aluminized in a vacuum chamber.
I imagine the process is quite different for metal. But they did it in Newton's time so it doesn't require a robotic precision router. It will definitely involve a ton of polishing, but there might be some casting or cutting first to start off with a closer shape.
>>958527
https://www.youtube.com/watch?v=4X6tNJpJY_A
https://www.youtube.com/watch?v=snz7JJlSZvw
https://www.youtube.com/watch?v=UfJ-i4Y6DGU
