irish amateur telescope makers?

jump234

anybody here build their own scope? (or know someone who did)

im considering building myself a 10" dobsonian, it doesnt seem too hard and I think id learn a lot more by actually doing it........

only thing thats holding me back is that I cant decide whether or not I want to grind my own mirror. If I did id save myself 200 yoyos and might learn something more. If i dont Id save myself a large amount of time and effort and perhaps save myself from fudging the whole thing up.

Grinding glass down to a perfect parabola is obviously no simple task. anybody out there tried and succeeded?

Seanie M

I built an 8" reflector about 8 years ago, building my second 8" at the moment. So I have a bit of experience...

Don't go down the road of grinding your own mirror (just yet). Its a tedious process, and unless you actually have a couple hundred yo-yo's to throw away, its not feasible when starting to build your first scope. There are some conditions you have to acknowledge, such as the cellar being the best place to grind, mistakes made may cost the whole mirror (at worst).

I have not done grinding, but I know a guy who has. He actually dug a large hole in his yard and made a cellar to do the grinding! Sounds mad, but you need a room with an almost constant temperature, even with hi-grade pyrex or low expansion glass.

I would recommend doing it sometime for a practice run, but unless you are experienced enough to do the mirror right, that you will actually use it, then you will spend more time and money grinding trying to get it right, then to actually buy the mirror ready silvered.

I have some of the materials, and an 8.5" blank, which, sometime, I am going to give a go.


Seanie.

jump234

cheers seanie, the more I read up on it the more enclined I am to agree with you. I might give it a go next time . I dont think the risk is worth it (this time).

out of interest where did you source the mirrors? Im looking at getting my mirrors off beacon hill telescopes in the uk. Pretty cool place who know their stuff. They have a finished 10" mirror plus flat for 274 sterling. not bad but i need to ship it here.

Im also thinking of getting my eyepieces from them (2 I reckon) and using a 12" pvc sewer pipe as the tubing. The mounting I can build.

If you wouldnt mind Id like to hear more about your scope. What materials did you use? does it work well for you? any problems encountered?

Seanie M

Thanks jump,

of course, it wasn't all smooth sailing, but I didn't have any major hiccups when I first built it. I made a skeleton tube from pipes and marine plywood for stability and ease of carrying - I couldn't get my hands on Wavin tubing, but I have it now for the revamp.
Through friends (aka contacts!), I was able to get 1" pillow block bearings for the declination axis, and oak wood and metal for the right ascension axis. Some of it was trial and error. The actual mount-cum-tripod was almost a unique design I made myself. But it was not a very practical one, so I am just going to buy myself a motoriszed EQ mount when the new tube assembly is finished (to know the weight etc.). I could spend almost as much making a proper mount, but I probably wouldn't have the accuracy for the tracking. The original counter weight was made from lumps of lead encased in cement - the bloody thing was heavy! But it stood up in gale force winds!
I used 0.9" eyepieces from a Tasco 3" reflector Santa got for me, in the 8". I made the focuser from fiberglass in a bean can, and lathed the desired shape out of it! A copper pipe of same outer diameter as the inner diameter I made in the focuser, was my eyepiece holder. I wrapped smooth felt round the brass pipe, and by friction I focused on my object.
Now, I have bought a proper rack-and-pinion 1.25" focuser, and new Celestron eyepieces to match.

It was fun making the original 8", but because I don't get much time to do it now, its not as fun. But, when I do get out into the garage and start on something, its hard for me to get away from it! I have plans to build a 12" reflector, or an 8" refractor after this one in a year or two. By that stage, I should almost be in a position to buy a house, and then think about building an observatory in the backyeard - now THAT will be fun!

I have pictures during the making of both scopes, something I would recommend onto yourself - you never know who you might show them to in the future, they not believeing that you built a telescope!

Also, a very handy book I got is The Standard Handbook For Telescope Making by Neale E. Howard. Its about 50 years old, but only materials have changed in building an amateur scope - not the scopes themselves! So its a sound read.

I'm far from being an expert in telescope making, but don't hesitate to ask (maybe in this thread? it would make interesting reading!) about things I did, or compare notes etc. You might also get some more joy if you logged onto www.irishastronomy.org (IFAS Homepage) - there are lots of other amateur astronomers there, and some who have built some scopes too!

All the best in your venture - it WILL be fun!


Seanie.

jump234

sounds like you were pretty creative in your design! Im following john dobsons plans pretty closely, with a few slight modifications, albeit mostly for aesthetics. So my design is sticking pretty much to the standard alt-azimuth mounting. no equatorial mounting or motorization this time round.

Id love to see the finished scope. You have a picture you can upload??? I especiallly like the fiberglass in a bean can bit

Ill let you know how i get on....probably on the ifas forums, username spudnik

cheers again

Seanie M

jump234 wrote:

Id love to see the finished scope. You have a picture you can upload??? I especiallly like the fiberglass in a bean can bit

I have photos somewhere. When I get a chance in the following few days, I'll seek them out and scan them in.

Tea drinker

I too am interested in building a scope (dob 6-8") as well, but as I am not that clever (!) I am a bit stumped on materials to use for the tube and rocker assembly. Anyone made a nice portable scope in that size? I'm interested in any recommendations / tips.

As regards the optics, anyone use orion optics UK?

I need something easy to handle as I drive to dark skies.

Seanie M

Tea-totaller,
for an 8" scope, you won't get a great deal of portability unless you made yourself a Schmidt-Cassegrain! (that divides the focal length in 2, thus halving the tube length). The problem you see is the focal length. Your average 8" mirror will be F8 (1600mm) or at best F6 (1200mm) focal length. To go for a smaller F number will mean more cost, and probably a little less on quality (the further a mirror is ground into a spherical or parabolic curve, the less accurate the light waves become).

My 8" scope tube is as long as I stand tall - 5ft 10"!! It will almost be the same for your Dob. Unless you go for a 6", but an 8" mirror, while only 2 inches bigger, collects almost 30% more light than a 6"!


Seanie.

Seanie M

Tea drinker wrote:

As regards the optics, anyone use orion optics UK?

Thats where I got my mirror and secondary mirror, from a chap by the name of Andy McCrea up in Belfast. When I first built it, he was a rep for them, and I already knew him, so it was plain sailing. He still stocks alot of their stuff. His website has been mentioned here in Astronomy threads somewhere, so I'd recommend going for that.



Seanie.

jump234

as regards the rocker assembly. For a simple alt-azimuth design your cant beat the tried and tested dobsonian design. For starters try here (plans)

sidewalk astro

and for more detailed and easier to follow plans, albeit for a smaller 4" scope, try here

4inch dob

havent started building my mount yet but im following those plans with a few slight modifications for my 10" scope

as regards the tube you're doing to need a tube 2 inches larger than the mirror. In my case I have a 12" pvc sewer pipe at least 63" long for a 10" F6.3 mirror. For a 6 or 8 inch mirror youll need a correspondingly large tube. I know pvc sewer pipes are sold in 4, 6, and 8 0r 9 inch as well as the 12" so try your nearest builder providers.....

Ive also seen a square wooden tube design constructed with a circular hole a t the front.....its here -> 6 inch F5

as i mentioned im also in the process of building one...the only progress so far is that I have the tube and I have the paint :rolleyes:

I'd like to hear what you opt for...so keep us posted

oh for the mirror you might also want to have a look at beacon hills pricelist(see my first post), at least for a price comparison if nothing else