Building a telescope some advice please

[rmhfsm]

Hi all. planning on building a ne telescope and wondered what advice is about for building them. What is best to buy the mirrors or buy blanks? Also is there any ideal sizes for the housing?

Cheers all

Rob

[barkis]

Hi. Rob.

I have made a few mirrors in my day, and telescopes too. If you are contemplating making your own mirror, and it sounds like it will be your first one, you will need to decide what diameter you want, what focal length you want it to be.

As far as the housing, I take it you mean the tube diameter. If it is the tube, then you will need to have the diameter at least 1 inch larger than the mirrors diameter. That will give a clearance all round of half an inch. You could have it larger, but the tube diameter will have a direct effect on the secondary mirrors size too.

If you need any more advice, just ask.

Ron.

[rmhfsm]

Thank You Ron, appreciated. Is it better to buy the mirrors do you think? I am looking at either an 8 or 12in diamiter at the mo. tho I might yet change to a 6in as it is my first and the 6in is ment to be the easiest. Any ideas on motor drives? I would like to make one of those as well and am sure it could be done with a small 2 or 3 volt motor but am currently unsure of the speed I would need to set it to. I am looking at Planets at the moment very interesting. can I get a toucam from newhere?

Rob

[GazOC]

I'm no ATM expert but I'd sort the mirrors and housing before you think about adding motor drives. Seeing as this will be the first mirror you've made I'd say that your two realistic options are to either make a 6" mirror with a longish focal ratio (say f8, larger focal ratios are easier to make) or buy a larger (8" - 12"), short focal ratio mirror set at around f5 which would be very difficult to make as a first project.

[barkis]

I agree very much with what Gaz has said Rob. First things first. Even if you buy mirrors ready for use, in the 8 to 12 inch range, the larger one will give some headaches as regards mountings. 12" is a very large instrument to accommodate on an equatorial mount, which is what you will need if you are looking to do astrophotography with it. The 8" would be a more realistic project for you I guess.

You could give yourself a test as regards finding out how determined you can be, and start by making yourself a 6" f8 mirror, as Gaz also suggested. Not too difficult a project for you, and you could make a Dobsonian mount for it just to put it to the test.

I take it you have done some homework on grinding and polishing/ figuring a paraboloid?. and therefore what is involved.

I am sure I saw a for sale of a 12" mirror and flat on one of the astro marts, but I can't remember which one.

Anyway Rob. You have decisions to make.

Ron.

[rmhfsm]

Thanks all for advice. I think I will go with it and try a 6" first tho I have a friend who posts in here that is going to help me with a 12" dobsonian as well. A little joint project as it were. Anyways I have done some home work on various telescopes and have found what seems to be a good guide to help in some area of the build as well as supplying basic programs which I may alter slightly as I go to help with grinding and calculations of that sort. I can put the address up if people are interested but I am not sure if it would be allowed at the moment (confirmation on this plz, Thanks ) I have built many things in my short life including a series three landy so another challenge is always good.

ta ta for now

Rob

[barkis]

Well, I wish you luck with your 6" project Rob. As long as you have access to blanks and grinding and polishing materials.

I have some 6"

[barkis]

I wish you luck with your projects Rob. As long as you have a resource for the materials you will need. I have blanks in my workshop, which I never got around to starting. Also loads of grinding powders from 80 grit down to the finest fine grind stuff. I also have some Cerium Oxide polishing powder I think. I have some optical pitch too, but I don't think I would risk using it, as I am not certain where it came from. It was a long time ago I acquired it.

Anyway, Good Luck.

Ron.

[GazOC]

I can put the address up if people are interested but I am not sure if it would be allowed at the moment (confirmation on this plz, Thanks )

Feel free.

[rmhfsm]

Thanks again, Would you be interested in selling the blanks and some of the grinding bits as I have not had chance to take the time to realy explore the market for these yet. will be a couple of weeks before I have enough money to buy bits tho so if you dont mind waiting barkis. :sunny:

Thanks too Gaz here is one of the many addresses I have found. Might be of some help to ppl. comments as to the site being any good always welcome too.

With thanks too Mark ii'm sure he wont mind the publisity.

http://telescopemaking.org/

Off too blow the clouds away too see jupiter now :jupiter:

Rob

[barkis]

Thanks again, Would you be interested in selling the blanks and some of the grinding bits as I have not had chance to take the time to really explore the market for these yet. will be a couple of weeks before I have enough money to buy bits tho so if you don't mind waiting barkis. :sunny:

Thanks too Gaz here is one of the many addresses I have found. Might be of some help to ppl. comments as to the site being any good always welcome too.

With thanks too Mark ii'm sure he wont mind the publisity.

http://telescopemaking.org/

Off too blow the clouds away too see jupiter now :jupiter:

Rob

Hi. Rob.

If you want to go ahead with a 6" mirror, I can put together a kit for you that will suffice to complete a 6" mirror.

I have a brand new 6" Pyrex mirror blank, and a plate tool, together with all the grinding agents you will require. Also some Cerium Oxide and polishing pitch. Everything you need to complete the job.

I had a look on Gavloptics website to price a 6" mirror kit, and I think their price is about £65 including postage.

I will do it for £30 including postage. You can let me know what you decide. I'll just leave you to think about it.

Cheers Ron.

[rmhfsm]

Wow thats a good price Ron,

Id pay for it now but I still havent been paid yet

If you wont mind I'll be happy to buy the said kit from you although it will be still be a short time before money arrives in my account.

I have started on the drawings now for the 6" dobsonian. I think it is going to be a skelital design with a couple of CPU or system fans to keep the jew at bay. More light and flexibility this way. I have had a few ideas about a drive system for it as well but will talk a bit more a bout that once I have over come a few minor problems with the setup.

Speak soon.

Thank Again Ron

Rob

[barkis]

Wow thats a good price Ron,

Id pay for it now but I still havent been paid yet

If you wont mind I'll be happy to buy the said kit from you although it will be still be a short time before money arrives in my account.

I have started on the drawings now for the 6" dobsonian. I think it is going to be a skelital design with a couple of CPU or system fans to keep the jew at bay. More light and flexibility this way. I have had a few ideas about a drive system for it as well but will talk a bit more a bout that once I have over come a few minor problems with the setup.

Speak soon.

Thank Again Ron

Rob

Rob, can I just ask if you have done any reading or researching on mirror making. Do you have any literature on the subject, and can I ask you where you are going to do the work. I really am just interested what you intend to do.

Also, I remember supplying mirror kits to three members of a local astronomy society, who expressed a desire to make their own objective, but unfortunately their interest plummeted when the work started. All I am saying is, although it is not expensive for the kit, it is a waste of money if it ends up in the bin. I just want to be sure you are as keen as you sound.

Ron.

[rmhfsm]

I have a workshop in my garage Ron. I have been doing a lot in research about all aspects of telescope making and the only worry I have is the accuracy I can make a mirror. I would like to make a couple of mirrors so I know exactly what I am doing when it comes to my 12". With a set of 6" blanks, I can make a small dobsonisn that will be good practice and resonable for my daughter to use. I will probably end up buying a set of 12" mirrors to be honest because of the accuracy I will require in my design. But the mirror making is a challenge that I am more then happy to undertake. It is something I can concentrate on instead of reading. (My Fiancee is fed up of me reading) bear in mind that I am an ex-mechanic as well as a cook so am extremely practice with my hands, I also make models of galleys in my spare time which requires great attension to detail and a lot of patience. Still not convinced?...

Not much else I can say really except that I know I need to be able to make a decent mirror in my project (sorry peeps no info on this 1) This is going to be completely custom made and hopefully will be finished in 2 years and in use.

Trust me Ron, I will make a pair of 6" mirrors for my dobsonian and I will get them perfect

[Doc]

I wish you luck Ron.

Please keep us informed as it's something I've always fancied doing but never got round to it.

I would imagine it's a lot harder then it sounds, especially if you are looking for something like 1/6 wave which is what a very good mirror should be around.

Anyway hope it all goes well.

Mick

[barkis]

I have a workshop in my garage Ron. I have been doing a lot in research about all aspects of telescope making and the only worry I have is the accuracy I can make a mirror. I would like to make a couple of mirrors so I know exactly what I am doing when it comes to my 12". With a set of 6" blanks, I can make a small dobsonisn that will be good practice and resonable for my daughter to use. I will probably end up buying a set of 12" mirrors to be honest because of the accuracy I will require in my design. But the mirror making is a challenge that I am more then happy to undertake. It is something I can concentrate on instead of reading. (My Fiancee is fed up of me reading) bear in mind that I am an ex-mechanic as well as a cook so am extremely practice with my hands, I also make models of galleys in my spare time which requires great attension to detail and a lot of patience. Still not convinced?...

Not much else I can say really except that I know I need to be able to make a decent mirror in my project (sorry peeps no info on this 1) This is going to be completely custom made and hopefully will be finished in 2 years and in use.

Trust me Ron, I will make a pair of 6" mirrors for my dobsonian and I will get them perfect

I sincerely hope I didn't give you the impression that I doubted your ability to make an astronomical mirror.

In my last post to you, I merely indicated the disappointment I felt, the last time I supplied mirror kits, and the projects were never finished.

I have read all your posts on this matter, and I know you will succeed.

One of the prime requirements in my estimation, is that anyone making a mirror, especially in the the latter stages of polishing and figuring, has to become as one with the task. You develop a feel for what is happening between the polishing tool, and the mirror's surface.

You get an Idea of what temperature can do to a mirrors surface, when testing as you try to achieve a perfect sphere, prior to parabolizing.

If you place your thumb on the surface of the mirror for a few seconds, then return to the Foucault tester to inspect that area, you will see a bump on the glass under the knife edge, as large as a mountain, The glass has raised up a couple of microns with the heat from you thumb.

But it looks huge. You then appreciate why allowing a telescope to cool to ambient temperature is very important.

It is a wonderful feeling, when you finally finish your telescope, and after seeing the great sights in the night sky. You give yourself a well done. You turned an ordinary lump of glass into a very precise optical instrument.

Ron.