1657Views17Replies

Author Options:

My big telescope project Answered

Picture of

I'm starting to design a very large telescope for my "backyard", ideally it will be a 1 meter (or larger) Prime Focus Telescope. I am in the process of engineering the primary mirror and have concluded that I need to create an array of small hexagon mirrors similar to the Keck Observatory but smaller. This will decrease the quality of the telescope but it will make the project affordable. The biggest problem with this design is that the mirrors have to be exactly placed and tilted to form the a perfect parabolic curve, and frankly I have no idea how to practically do that. If anyone has an idea about how this can be done or questions about my project i would be glad to hear from you.

17 Replies

user
mcolosim (author)2010-12-07

I know this is a bit old however I just came across it... try you normally want your lens to have a focal length of 6 to 8 times the width of lens. Creating a the before mentioned ratio of 1 to 6 or 8 will make a much flatter base reducing your error with flat mirrors.

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)mcolosim2010-12-07

The current thrust of large amateur telescopes is FAST, not F8, more F2- F2.5. A 1 metre class F8 would be 8 metres to prime focus, a little awkward to move around.

Select as Best AnswerUndo Best Answer

user
mcolosim (author)steveastrouk2010-12-08

very true a F8 or F6 telescope with a 1 meter lens would be quite the sizable scope. however there would be to much error with flat mirrors to create a F2 . it may be able to be done with much smaller mirrors I'm not sure how the seams of that many mirrors would effect the picture.

Select as Best AnswerUndo Best Answer

user
steveastrouk (author)mcolosim2010-12-08

Yes, I take your point.

I'm peripherally involved with the "Alt-Az initiative", an international group trying to lower the costs of lots of aperture.

The multi-mirror scopes seem to all be based on SPHERICAL optics, with correction systems in the secondary and tertiary optics.

Select as Best AnswerUndo Best Answer

user
CameronSS (author)2009-02-28

What if you put the mirrors on adjustable mounts? They could be tweaked by hand to get the most perfect alignment possible (not much more effort than collimating).

Select as Best AnswerUndo Best Answer

user
lemonie (author)2009-02-24

One way of creating parabolic sursaces is to spin a dish of liquid.

Related

If you could spin a tray of e.g. epoxy resin, you might hope for it to set in a useful parabolic dish

L

Select as Best AnswerUndo Best Answer

user
E-R-IC (author)lemonie2009-02-28

it would have to be flawless, or it would reck the mirror, much like hubble

Select as Best AnswerUndo Best Answer

user
Kiteman (author)lemonie2009-02-24

That needs an insanely* stable turntable, plus incredibly fine polishing afterwards.

*That's a metric "insanely".

Select as Best AnswerUndo Best Answer

user
SolarFlower_org (author)2009-02-25

I've been wanting to play around with tesselation and constructing parabolic dishes for a while, so I took this as an excuse. In my CAD package (Rhino3D) I had a quick mess around making a parabloic shape out of hexagons, and this was the result. One issue immediately comes up; making this from flat mirrors is going to make it harder to construct and a lot less accurate. The hexagons in my model are irregular (not perfect hexagons) and the're not all the same. I'm not sure if it's possible to do this with regular identical hexs, you may have to ask a mathematician. I placed them by hand and shifted the edges until they were pretty much good enough. The yellow lines are light rays, as you can see they really don't converge nicely at all. If you wanted to make a solar oven or something this would be proabably good enough, but for a telescope I just don't see it working. I'm not sure what the Keck guys did, but I figure they must have used curved hexagons. Doing it that way would make the focus and tesselation perfect, but means you have to make perfectly and individually curved surfaces, which kind of defeats the purpose. So, basically, no. BUT There are other ways of making large parabolic dishes. The easiest would be to get a large satelite dish and cover it in strips of mylar (from your local hydroponics store, very cheap). Otherwise, I plan to make one in the next couple of weeks, using a sort of cradle of interlocking slats supporting a dish of shaped strips. It's a little hard to explain but I might do an instructable on it if I get around to it. Hope this helps, if you (or anyone else) want the model file just let me know.

Select as Best AnswerUndo Best Answer

user

Oops ...........this was the result.

Select as Best AnswerUndo Best Answer

user
Twlight (author)SolarFlower_org2009-02-25

Yeah I relieved i made a gross miscalculation with my initial design and I'm having to rework my original idea, I'm thinking about using a curved lens to better converge the light from the mirror Array, and using alot more mirrors then I initially thought. But as of know my prime focus telescope is on hiatus

Select as Best AnswerUndo Best Answer

user
SolarFlower_org (author)Twlight2009-02-26

What kind of curved mirror? I'm not sure there's anything that'd make sense of what's above. That design uses 101 mirrors, even if you tripled that, it still wouldn't be accurate enough. Triangles would work better, but really you need curved surfaces.

Select as Best AnswerUndo Best Answer

user
Twlight (author)SolarFlower_org2009-02-26

I'm still working on the lens but what I'm thinking is using a large fish eye(or fly eye) lens to re focus the light from the mirror . I'm also thinking of using alot of smaller mirrors and a dish with less depth to help with the resolution. I haven't tried it in Rhino yet but I'm not to confident it will work and even if it does I don't think I'd be able to afford the giant lens I'd need. So I'm basically scraping this idea for the mirror. But I am still interested in making a large telescope I am just not sure how I'm going to make the mirror anymore.

Select as Best AnswerUndo Best Answer

user
Twlight (author)Twlight2009-02-26

So I tried everything I could think of with rhino and I cant get it to work good enough with flat mirrors. So it looks like its back to the drawing board.

Select as Best AnswerUndo Best Answer

user
Lithium Rain (author)2009-02-24

How about getting an old satellite dish and gluing mirrors to that?

Select as Best AnswerUndo Best Answer

user
Twlight (author)Lithium Rain2009-02-24

Thats a great idea thanks

Select as Best AnswerUndo Best Answer