Assembling a refractive telescope Mid end

[shyam]

Hello

I wanted to assemble a refractive telescope astronomical with a good viewing of milky way and other entities . This is for reason , one is i will have the knowledge while assembling it so any issue can solve it myself, secondly very important the cost

can any one help in

thanks

shyam menon

[DirkSteele]

There a book on that topic.  http://www.willbell.com/tm/refractor-telescope.htm

 

Quite want to read it myself though I doubt I have the technical ability to complete the project,

[ronin]

If you mean "make" as in make your own lens then seriously forget it, you will not have the required lens grinding equipment. After which you need the different glass types. The easy part is the maths to determine the required radiai and seperation of each element, this comes after the glass types as the maths and resultant radaii are dependant on the refractive indices of the glass.

Buying one is easy, try Surplus Shed. The internal construction is easy as it is almost always a Fraunhoffer arrangement. So the lens order and orientation is easy/well defined.

The rest is basically mechanics, the center line length of the tube+diagonal+focuser has to add up to the focal length of the lens. The focal length is measured from the center of the lens assembly not the rear glass face. The focuser length is bes t measured when the focuser is at it's mid point - just allows kind of best adjustment later.

[John]

Making the objective lens for a refractor is a very specialised task however building a refracting telescope using a surplus objective lens and, say, an old binocular or microscope eyepiece is relatively straightforward. Here is a web article on how to build a small refractor telescope:

http://www.skyatnightmagazine.com/feature/how-guide/how-make-small-refractor-telescope

I would think that the first thing to do is to think about where you might be able to acquire a suitable objective lens and eyepiece to use in the project.

Good luck !

[Chris]

Can you clarify a few things, i.e. do you want to buy the lens and build the optical tube and focuser etc, or do you want to make the optics also. 

If you want to make the optics I would start off by making a Newtonian parabolic mirror to hone your skills, this is exactly what it recommends in the Will Bell book. There is a huge amount of info on the web about grinding mirrors, even quite a bit on SGL in the DIY section. Not that much info on the web about grinding lenses. I've started with a 8.75" mirror, after which I'll be moving onto grinding polishing and figuring a 5" doublet achromat lens from blanks that were very kindly donated to me. 

I wouldn't say flat out forget it, but it's certainly a big challenge! all depends on what resources you have available and how tenacious and patient you are. Lots of free time would be a bonus, I don't have a great deal so I'm still only on the fine grinding 6 months into my mirror. 

If you want to buy a lens there a places we can recommend if you clarify this is the direction you wish to take. This is the much easier/less crazy option lol  

[Cosmic Geoff]

When I was a teenager, I re-figured the mirror of a cheap 4" reflector and made a new wooden tube for it, and made up the other fittings and an alt-azimuth mount. Then I made an 8" reflector, including grinding and polishing the mirror and making a wooden tube and a fork mount.  Would I consider doing the same today? Not for a second. In the intervening years, astronomical telescopes have become far more affordable, and more sophisticated designs are available.

Making a lens yourself is a no-no. Even if you have the skills, you have to make four precision surfaces for an achromat, compared with one for a mirror. For the mechanical parts, without access to a machine workshop you will be restricted to what you can make or improvise by hand. In the past week, I made a set of tripod legs. I had to buy wood and metal and bolts, and I had access to an electric pillar drill and an electric router. It took quite a few hours. If I had access to a better workshop, I could have made a neater job of it, and without the power tools it would have been worse.

If you are determined to make your own refractor, I suggest you start by acquiring the biggest objective lens you can afford. Otherwise there will be little or no benefit over buying a second-hand instrument.  When I sold a 70mm refractor (complete with mount and eyepieces) on ebay I got just £25 for it, which will indicate just how little small used refractors can be worth. 

[Chris]

3 hours ago, Cosmic Geoff said:

When I was a teenager, I re-figured the mirror of a cheap 4" reflector and made a new wooden tube for it, and made up the other fittings and an alt-azimuth mount. Then I made an 8" reflector, including grinding and polishing the mirror and making a wooden tube and a fork mount.  Would I consider doing the same today? Not for a second. In the intervening years, astronomical telescopes have become far more affordable, and more sophisticated designs are available.

Making a lens yourself is a no-no. Even if you have the skills, you have to make four precision surfaces for an achromat, compared with one for a mirror. For the mechanical parts, without access to a machine workshop you will be restricted to what you can make or improvise by hand. In the past week, I made a set of tripod legs. I had to buy wood and metal and bolts, and I had access to an electric pillar drill and an electric router. It took quite a few hours. If I had access to a better workshop, I could have made a neater job of it, and without the power tools it would have been worse.

If you are determined to make your own refractor, I suggest you start by acquiring the biggest objective lens you can afford. Otherwise there will be little or no benefit over buying a second-hand instrument.  When I sold a 70mm refractor (complete with mount and eyepieces) on ebay I got just £25 for it, which will indicate just how little small used refractors can be worth. 

I've got to agree that amateur telescope making isn't generally about saving money now days. China make such excellent telescopes so cheaply now we really are spoiled compared to decades ago.

 I think people now days do this kind of thing for the achievement and satisfaction rather than money saving. I think money saving does come into the equation with mirrors say 14" and above, whereas my 8.75" has already cost me the price of a Synta 8" mirror plus a solid weeks worth of labour so far if I add it all together.  

 "Making a lens yourself is a no-no. Even if you have the skills, you have to make four precision surfaces for an achromat, compared with one for a mirror".

Bear in mind that each surface only needs to be spherical rather than parabolic, and you can match radii by grinding one piece of glass with the other...well at least with the Littrow design from what I understand so far. Furthermore, with that design of achromat one surface (s4) is flat  

[Chris]

Stellafane is an excellent resource for amateaur telescope making. It also shows whats possible to achieve. I'm not saying make the optics as its a tough route, but if you find this is what you want to do then Stellafane is a good resource to have at hand   

https://stellafane.org/tm/tg/beveridge/beveridge.html

https://stellafane.org/tm/index.html

 

[shyam]

On 12/7/2017 at 15:36, Lockie said:

Can you clarify a few things, i.e. do you want to buy the lens and build the optical tube and focuser etc, or do you want to make the optics also. 

If you want to make the optics I would start off by making a Newtonian parabolic mirror to hone your skills, this is exactly what it recommends in the Will Bell book. There is a huge amount of info on the web about grinding mirrors, even quite a bit on SGL in the DIY section. Not that much info on the web about grinding lenses. I've started with a 8.75" mirror, after which I'll be moving onto grinding polishing and figuring a 5" doublet achromat lens from blanks that were very kindly donated to me. 

I wouldn't say flat out forget it, but it's certainly a big challenge! all depends on what resources you have available and how tenacious and patient you are. Lots of free time would be a bonus, I don't have a great deal so I'm still only on the fine grinding 6 months into my mirror. 

If you want to buy a lens there a places we can recommend if you clarify this is the direction you wish to take. This is the much easier/less crazy option lol  

hi

i am looking at assembling lens . kindly let me know the source to buy lens and other accessories in making of a telescope

regards

shyam menon

[John]

I think this supplier is in India:

http://www.tejraj.com/optics.html

[Cornelius Varley]

A few vintage designs https://www.vintageprojects.com/telescope-plans.html