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View Full Version : homeshop telescopes - need some guidance & advice



Mcgyver
01-15-2007, 01:08 PM
my 14 year old is interested in a shop project, we've talked about it and she thinks a telescope would be a neat idea. We've both been reading web sites and think a Newtonian reflector is probably the way to go, with a purchased mirror.

Evan I know from previous posts you have a lot to offer in this area - are the other astronomers on the board

There's lots of great content on the web, but mostly from peoples shops with a drill press and router....What I've looking for is build/design ideas and recommendations that take advantage of the more specialized skills and tools a home shop machinist has and from people who are a little more tech savvy (not that I'm looking to over complicate mind you).

Secondly, any good places to source the mirrors and eyepiece? trying to keep costs down.

thanks in advance

halac
01-15-2007, 01:42 PM
A good Google search on "Astronomy supplies" will give some sources such as http://www.seasky.org/index.html

You also might look to see if there are any astronomy clubs in your area. When I was into the hobby I learned a lot from its members. They even had telescope making classes. They would help you grind your own mirrors which were usually much better then commercial made ones.

dp
01-15-2007, 02:47 PM
Dobsonian telescopes are the very easiest to make. It is the mount/movement that is the hard part and the Dobby is just a tube sitting on pegs rather like early lug-mounted cannons. Steve Bedair's web site has good info and links on building mounts. http://bedair.org/ScopeStuff.html

I have an 8" Dobsonian and it has been a lot of fun over the last 25 years I've had it. Conveniently, a common frisbee makes the perfect cover for it.

Evan
01-15-2007, 03:51 PM
I agree on the Dobson design. Easy to build and easy to use. Good for visual observing but not for photography as it is more difficult to fit a tracking system. With a dobsonian you get much more bang for your buck and you can get as complicated or simple as you wish.

This scope that I just posted in the other thread is a dobson type. As you can see the amount of machining you can put into it is up to you.

http://vts.bc.ca/pics/bpscope1.jpg

That scope is intended for extreme portability. One thing to keep in mind is that the easier the scope is to set up the more you will use it.

For mirrors and parts kits I recommend

http://www.e-scopes.cc/

It's where I purchased the mirrors for my six inch scope and I am happy with it.

BobWarfield
01-15-2007, 04:38 PM
Mcgyver, that's great news that your 14 year old is interested in telescopes and in the shop!

I've been fiddling with telescopes since the third grade, and ironically my first exposure to machine tools came from astronomy way back then. My dad took me around to machine shops to help me build a mount for the scope. The very first one we met a machinist named "Charlie Brown" who took an interest in it and turned the shafts I needed for free. I remember vividly watching that smoke coming off as he turned it on the lathe and thinking that there must be some kind of awesome power tied up there.

As to what to build, Dobsonian Newtonians (there's a redundant but catchy turn of phrase) are absolutely the easiest, but they don't necessarily take advantage of what a machinist has to offer. They were created largely because most amateurs did not have access to machine shops but wanted the "best" possible telescope. Many are made from plywood. They certainly are useful deep sky (e.g. dim object) instruments, but there are other possibilities to consider. The sky is the limit on what you can do with machine tools at hand.

Here are a few other thoughts:

- Make a scope with a true equatorial mount rather than the Dob's altazimuth.

- Make a cool binocular scope of some kind. Binoculars trick the eye into seeing things that are hard to see out of one eye, and most people find the more comfortable. I have sometimes daydreamed of making a motorized altazimuth couch where two people could share a big set of binocs and scan the heavens in comfort.

- Consider a refractor. You can purchase the lenses (astronomers call them "objectives") already to use. You will need to house them. Refractors are more versatile than a big reflector as they are generally more satisfactory for terrestrial viewing. Many people think that for a given size, the refractor yields a better visual image, particularly for planets. This is because they have no central obstruction and so have the potential to create higher contrast images--key for looking at planets as well as recognizing dim objects.

- More exotic scopes are available to the machinist. For example, google the "schiefspiegler", which is a mirrored telescope with many of the advantages of a refractor.

- How about a Newtonian with equatorial mount, but that breaks down for easy travel into fitted cases? One sees these from time to time and they are jewels of mechanical construction. Very clever, impossible without machine tools.

- Like the refractors and Dobsonian reflectors, you can get off the shelf optics for most kinds of telescope. It's only a question of cost for more exotic designs. You may wish to investigate Cassegrain scopes, which are another that has a lot of advantages.

Just for fun (not suggestion you build this!), here is an "extreme" astronomy + machine tool site:

http://www.observatory.org/install.htm

Scroll down to the "Unique 10" Fork-Mounted RC Scope", it's nuts!

In the end, the Dobsonian will be easiest, but I wanted you to see the potential once you have access to machine tools.

There are many other astro-machiners out there who may provide inspiration:

http://www.dragonworks.info/

http://www.stellar-international.com/lathe.html

http://bedair.org/ScopeStuff.html

http://www.jeffalbro.net/

http://astro.neutral.org/

http://www.focuser.com/atm/anodize/anodize99.html

http://homepage3.nifty.com/rockhill/ (requires Babelfish!)

There are many others, but those stuck in my lists of links. Keep us posted!

Best,

BW

Evan
01-15-2007, 05:07 PM
Van Slyke does produce some nice stuff. He also has a very high opinion of his work.



No I will not build another one - not ever again! Too much effort! This scope has build-quality and features that even God hasn't conceived (explained in depth below).

BobWarfield
01-15-2007, 06:19 PM
Van Slyke does produce some nice stuff. He also has a very high opinion of his work.

It's a bit much in the end of the day, good mostly for bragging rights. But, it is entertaining to look at.

Besides, I've seen pix of Mcgyver's work--he can make that stuff too!

Best,

BW

lenord
01-15-2007, 10:43 PM
Mirror grinding a small 6" mirror is not that hard to do if you have someone local to teach you. Our local astro club has someone who does just that. He and a newbie ground a 6" mirror (mostly) during two of our meetings. A 6"or 8" is a good size to start with too. Evan is right, get the size you will use the most.

Usually local astro clubs have star parties where you can go look at other scopes, commercial and home made. GOOD source of ideas there.

You might look on www.bbastrodesigns.com (http://www.bbastrodesigns.com) and look there. Mel has written a lot of articles you can read there. Lots of ideas and info there. Not just GoTo scopes either.

You can make a dob mount full "GoTo" if you want to get into making gears or friction drives and using electronics and motors. Long exposure CCD work is limited on a dob, until you make a field de-rotator, but it can be done. A GEM is easier to use if you want to take long exposure pics of what you see.

Eyepiece(s) you will want more than one !
More likely a set or two. Prices range from $25.00 to over $400.00, EACH. Again, star parties with people you know is a great place to get an idea of what you want to spend and get in quality for eyepieces. Remember the barlow.

Two things I would have done differently had I done the proper research.
1. 2" focusers and eyepeices are the way to go. Forget about 1.25" eyepieces. (the wow factor)
2. Don't waste time on a manual scope if you live in light polluted skies. Get digital setting circles at least or a GoTo scope. If you live out in the country, get a good skychart and a Telrad like device.

Sources for mirrors and eyepieces:

www.astromart.com (http://www.astromart.com) --astro-ebay
www.astronomy-mall.com (http://www.astronomy-mall.com) --like the ebay stores for astronomy
http://www.fpi-protostar.com/ --secondaries/spiders
http://www.siebertoptics.bizland.com/ --eyepeices
http://www.pegasusoptics.com/ --mirrors
http://tfn.net/~blombard/ -- good links page


FWIW
Lenord

Paul Alciatore
01-16-2007, 12:28 AM
..... For mirrors and parts kits I recommend

http://www.e-scopes.cc/

It's where I purchased the mirrors for my six inch scope and I am happy with it.

Evan,

You didn't grind your own mirror. I am shocked!



But thanks for the URL.

Evan
01-16-2007, 12:46 AM
I'm a perfectionist, not a masochist.

dp
01-16-2007, 12:55 AM
I'm a perfectionist, not a masochist.

Then you are both. Perfection is unachievable and those who pursue it are doomed to failure.

Think I read that on a fortune cookie.

Mcgyver
01-16-2007, 07:31 AM
guys, thanks a lot for all the thoughtful info and suggestions - much appreciated!

Bob, some of those projects in the link looks amazing! thanks for the compliment, and as interesting as they look, I have to avoid the 5 year Van Slyke type project for another day... its too ambitious a project for a starter for someone who is just finding out whether they like shop work. Its looking like the Dobsonian style to start with. besides, 6" tapered roller bearings and 2" thick slabs of titanium are not in the budget!

I appreciate all the ideas and help

rantbot
01-16-2007, 11:06 AM
Shops and telescopes seem like naturals, but they don't really mix all that well.

I always have the 13 inch reflector apart because I'm making some doodad or other for it, or I'm improving some doodad I made before. It never stops. When it's together it's pretty nice. I have a 4 inch reflector mounted on it in such a way that I can use it as a finder, or when I'm showing something to somebody else I can use the 4 inch while they look at the bright image in the 13 inch. That way I can guide the whole kaboodle as well. It beats standing around with my hands in my pockets telling them what they should be seeing if they hadn't knocked it out of the field of view while trying to focus the eyepiece.

Anyway, pieces, no matter how good, are no good for gawking through. So when I want to look at something I have to use my cheapo Chinese 80mm refractor, which has the great merit of being together in one piece.

demerrill
01-16-2007, 06:15 PM
Regardless of what telescope type you decide to build, I suggest you start out by reading http://www.willbell.com/tm/dobtel.htm

You will see that there are plenty of opportunities for machine work on even this simple design. You'll see stars sooner and it can be refined, remounted, etc later if your interest dictates.

David Merrill

lenord
01-16-2007, 06:33 PM
Darn it, I forgot to mention that book.
I second that recommendation.

Lenord

Evan
01-16-2007, 09:17 PM
Here is another link especially suited for those building a first telescope. It is the pages of Professor Dave Trott. He invented the double arm drive concept that I used as the basis for my high accuracy implementation of the device. He says that as far as he knows it is the most accurate version of his device ever built.

http://members.aol.com/_ht_a/davetrott/page1.htm

Mcgyver
01-16-2007, 10:37 PM
Evan, you were too modest, you didn't post the link to your own design!
http://vts.bc.ca/astrophoto/scope.htm

I think I've seen it here before, but either hadn't looked closely enough or had forgotten how nice it was. couple of questions; how are the carbon fiber rods held at there ends and the carbon fiber rods (what dia btw) don't seem to intersect the mounting rings in the middle of the telescope?

Dick Plasencia
01-17-2007, 12:30 PM
Evan,
If you don't mind I would like some construction details on your portable DOB. I'd like to "borrow" some ideas for a similar project.
I'm particularly interested in the colapsible "tube" assembly. Also have a question on collimation when you get it set up. Are you showing it without the focuser or is that something you take off for travel?

Rex
01-17-2007, 03:36 PM
I saw some telesope plans (several) on alt.binaries.e-book.technical today

Evan
01-17-2007, 04:13 PM
I didn't make it clear but the portable dob isn't mine. It's a scope I saw at the Mt. Kobau star party a couple of years ago and I don't know any more about it than what you see in the pics. I pissed the owner off when I asked him permission to touch it (he agreed) and immediately investigated how much torsion it took to misalign the secondary/eyepiece mount. It's definitely a weak point in the design and I would at least triangulate it in some way.

What I didn't know is that he was on the judging committee that evaluated the attendees efforts including my scope for the mechanical excellence award. Needless to say I didn't win an award that year. :rolleyes:

Mcgyver,

The rods are two diameters. The angled truss rods do not attach to the mounting rings but pass within them. They are a press fit in the ferrules at both ends. The smaller rods are .250" OD and the larger rods are .410 OD. The larger rods are parallel to the optical axis and pass through nylatron clamping blocks that are attached to the two mount rings. By loosening thumb screws on the clamp blocks the scope can be instantly balanced for larger or small eyepieces etc by sliding it back and forth in the mount ring.

While it may not seem like a very stable method of mounting the scope you need to understand the characteristics of hollow graphite/epoxy tubing. It is enormously rigid with very little flex under load. Those 4 large tubes can each take a 1 kilo load in the center with the ends supported and show a maximum deflection of around .020". Total deflection of all four under the 1.6 kilo weight of the rest of the scope is about .008" maximum. Damping time when nudged is about .5 second as graphite/epoxy has excellent damping.

Another reason for using the graphite/epoxy is the light weight. All the rods put together weight only about 10 ounces. Yet another reason for using it is that is has a very slightly negative coefficient of linear expansion with temperature. The telescope is calculated to stay almost precisely the same focal length over a 100 degree temperature range. This is the same technology used in the Hubble so it wasn't my idea.

Mcgyver
01-17-2007, 06:46 PM
thanks, makes sense now. wasn't sure i was seeing it correctly, sent you a PM