Building my own telescope project.

[thumper235]

A few months ago I got a cheesy department store run on the mill telescope made by meade. Well, It was a test to see if I would actually use it like I had invision up in my brain. Turns out, I use it frequently as in 2-5 times a week at minimum. So there is a guy on youtube named Tony Darnell, and he is a space geek who has a website with cool info. So, searching around on it I got to his write up on how to select a telescope. After reading his write up, I went to look at prices and.... WOW.

So, I decided to build my own telescope. Not only will I get the satisfaction of knowing I made it, but the educational experience from doing it would be awesome. Perhaps I will pickup some of that cool useful and useless knowledge to spit out at random times to people.

So here is the point of this thread. There are MANY instructions floating on the internet of different builds one could do. My goal is to build something portable enough that I could pack it in my car yet powerful enough to really be in shock-n-awe at what I see. I mean, mars is frickin awesome, but when you only see a small orange speck it is not as satisfying.

So would you all mind shooting out some ideas on which build plans you think are cool?

 

[RisingFury]

I would strongly advise against building your own telescope. There are two big reasons for it:
- You'll need to buy the optics, because you can't make lenses and / or mirrors yourself. Optics elements are the most expensive pieces of the telescope anyway, so even if you get them cheap, you'll only be saving the cost of the frame - max.
- Factory built scopes are put together very accurately and you really want accuracy when you're dealing with optics. Half a millimeter precision just isn't good enough, you need to be as precise as the length of the light you're watching.

If you want to see Mars as more than an orange speck, you'll need a high powered telescope. I'd suggest you save up money for it and really buy as big as you can get. About 12" to 15" mirror is the maximum an amateur should use, but these cost in the 5000 USD range.

A few members here own large telescopes (large is ~8" or more) and can give you better info about how such telescopes handle.

 

[jarmonik]

I had a similar project once. The optics is not a problem you can make a high quality mirror by hand. All the stuff you need is easily available and there are a lot of articles about mirror grinding in the internet. But unless you want to do it for a fun it's really not worth for a money and you may need to make few mirrors for a practice before the "real" one. Buying a mirror is more time/cost efficient.

The real problem is the mounting and tracking system. High precission gears and bearings are highly expensive. The easiest and cheapest way to get those parts is to by a factory made mounting and dismantle the parts you need. And that's the point where I lost my interest to the project.

EDIT: You may be able to make the mirror and the tube but you need to buy a proper focuser and mounting.

 

[n72.75]

Gears aren't hard if you have four axis milling machine ...

 

[RisingFury]

The optics is not a problem you can make a high quality mirror by hand.

I very much doubt the high quality part. If you want a high quality mirror, it needs to be ground down so that the largest error in the mirror has a size of 1/8 of the light's wavelength. For optical light, we're talking about 50 nanometers for blue light.

On top of that, the mirror should be comma-free, so you're talking about a parabolic mirror, not a spherical one. The only "easy" way I know of that will make such a shape is if you take a liquid that hardens slowly and spin it. But that will only get you down to about 100 micrometer error range, you still need to grind it down and that's no easy task.

---------- Post added at 11:23 ---------- Previous post was at 11:21 ----------

Gears aren't hard if you have four axis milling machine ...

Ah, yes. I'll just pull one out from my basement. Everyone has a four axis milling machine in their basement!

 

[jarmonik]

On top of that, the mirror should be comma-free, so you're talking about a parabolic mirror, not a spherical one. The only "easy" way I know of that will make such a shape is if you take a liquid that hardens slowly and spin it. But that will only get you down to about 100 micrometer error range, you still need to grind it down and that's no easy task.

True, It's not an easy task but doable if you have the patiency. Also the difference between a spherical and a paraboloid mirror is somewhere around 80 nanometers not 100 micrometers. So, a spherical mirror alone can take you to 1/5 of the wavelength of the light unless I am mistaking. But that, of course, depends about the size and the focal length of the mirror.

 

[RisingFury]

No, 100 micrometers is the error caused by a hardening liquid like epoxy, when creating the parabolic shape. That error is already huge. It must not be higher than 50 nanometers in order for the mirror to meet the Rayleigh criterion.

The problem with a spherical mirror is that it does not focus all its light in one spot - not even a perfect spherical mirror would. A parabolic one would. The error from the spherical mirror is called a comma and it basically smudges the image slightly. The larger the mirror, the worse the error is.

 

[thumper235]

Just a little update. Inb4 Necro.


Dobsonian is the way to fly it looks like. There are various how-to's on the net and it looks fairly simple. Looks like I need to just put in the time. I need something to hold me over until I can save up for that Snazzy Takahashi.

The one I have been looking at looks like I can get everything from Homedepot, and just order my optics online. It involves using a concrete forming tube. Im sure most of you know what type this is.


I think this will be a decent enough one until a better one comes along. Heck ANYTHING is better than what I have now. It really stinks getting jupiter in semi focus only to have it roll away in 5seconds or so.