How to make telescope

[Lab King]

how can i make a telescope with ophthalmic lenses
I have upto +20.00 or -20.00 lenses
can any one tell me what power is required and the distance between 2 lenses

[Navion]

http://www.pacifier.com/~tpope/Build..._Telescope.htm Try this,We made a bunch of lenses for a local school last year, they seem to be happy with it

[Darryl Meister]

In addition to the Galilean telescope described in the very nice link provided by Navion, you can also make a Keplerian or terrestrial telescope using a strong plus (for the eyepiece) and a weak plus lens (for the objective). Objects will be upside down with this type of telescope though.

For both the Galilean and the Keplerian telescopes, the magnification is equal to the ratio of the power of the eyepiece to the power of the objective and the tube length, or separation between the lenses, is equal to the sum of the focal lengths of the two lenses (using a negative focal length for the minus eyepiece lens in a Galilean telescope).

[HarryChiling]

This may not help since it would require more than lenses but try a search for a dobsonian telescope, they are fairly easy to make and very powerful.

[Darryl Meister]

Just keep in mind that Dobsonian and Newtonian telescopes are reflector telescopes, not refractor telescopes, so you will need a large concave mirror in addition to the eyepiece lens assembly.

[Jacqui]

Daryl: I realize that it would have limitations, but why couldn't a 75 - 80mm glass ophthalmic lens blank be used for the reflector mirror?? They should still be available from X-cel, although may be a special order. It would be an interesting project for a beginner at a possibly lower cost.

Also mirror coating: Where can someone get a mirror silver coated or can an ophthalmic coating be used?? Is a mirror coating like on eyeglass lenses smooth enough??

[rbaker]

A sphere would have excessive aberrations. Ophthalmic coatings would not do the job.

Fabricating a 6" mirror is a relatively easy job. Edmond's Scientific has everything you need and there are tons of books available.

[Darryl Meister]

I realize that it would have limitations, but why couldn't a 75 - 80mm glass ophthalmic lens blank be used for the reflector mirror??

If you have it mirror-coated, I don't see any reason why you couldn't use a lens blank. Just keep in mind that it won't have the same light gathering properties or field of view of a regular mirror. Vacuum mirror coatings typically transmit some quantity of light and the limited blank diameter will also put a lens at a disadvantage compared to typical telescope mirrors.

Dick's suggestion about using something from Edmund Scientific is probably more practical and cost-effective.

[fooliisa]

1) Acquire a pair of lenses - a large convex lens and a small concave one. Convex lenses are thicker in the center than at the edge; concave ones are thinner in the center.
2) Find two cardboard tubes that will allow one to slide inside the other.
3) Figure out how far apart the lenses should be by looking through the smaller lens while holding the larger one out in front of you. When you can focus on an object in the distance, measure how far it is between the two lenses.
4) Double that measurement. The length of the two tubes should be about this long.
5) Fasten the larger lens on one end of the wider tube. Hot glue is good for this.
6) Mount the smaller lens at the opening of the smaller tube. This is the eyepiece.
7) Build a gasket from cardboard or Styrofoam if the tube opening is larger than the lens.
8) Make sure the lenses line up with each other. The centers should be in the centers of the tubes and the lenses should be parallel with each other.

[One science]

how can i make a telescope with ophthalmic lenses
I have upto +20.00 or -20.00 lenses
can any one tell me what power is required and the distance between 2 lenses

Prince A.m Khan
princeamk@yahoo.com
0092-321-2482418

But what kind of telescope do you want to do? refractory telescopes, reflected telescopes, optical telescope, infrared telescope...?

[Uilleann]

Ophthalmic and astronomical mirror silvering processes and materials are quite different. The astro varieties often use a thin layer of vaporized aluminum. It's an extremely reflective surface, but also extremely delicate. Quite different from the mirroring on a sun lens for example, which are designed to allow a good portion of light through.

[Barry Santini]

The surface of a mirror in a classic reglecting telescope is parabolic is profile. Ophthalmic lens surfaces are not. The magnification is a ratio between the focal length of the mirror and the eyepiece. The effective aperture is the ratio of the mirror's diamter to its focal length. Anything shorter than f/8 is not a project for a first time amateur to attempt and get good image results. So, an 80mm lens with a concave surface radius of 640mm (approx 1.5 diopters) is suitable. But the temperature and mechanical stresses and flexure of a standard ophthalmic lens would make it ill suited for use in a reflecting telescope. Refractors, now that's another story.

For this hypothetical telescope of 80mm and f/8 (refracting or reflecting), for just 15x you'd need an eyelens (eyepiece) of approx 43mm focal length (about 23 diopters). This would be termed a "richest-field" telescope, as its low power and wide field of view would present many stars to the observer. A simple meniscus ophthalmic lens of this power and shape would result in a sever mismatch of eyepiece and objective focal plane curvatures, thereby significantly reducing the acceptably sharp FOV, not to mention the lateral chromatic aberration that would further deteriorate the perpheral image quality. And off-axis astigmatism from the eyepiece would leave a useful apparent FOV of about 12-15 degrees.

Why bother? Just for a kick?

Visit www.televue.com for all the info you could ever want on telescopes and eyepieces. Start here: http://www.printthis.clickability.co...66&cid=3311076

B

[Sanchez]

It is a simple construction of the telescope. This telescope can be extended to various other purposes, to make a better telescope. This telescope can give a clearer picture of objects.

[CEO]

My Dad made me and my friends build our own telescopes completely by hand by grinding and polishing our own glass all the way from 3" coasters for furniture to 24" telescopes. One interesting side note, one of the neighborhood kids who we built telescopes with was David Brin...who became astrophysicist and Hugo Award Science fiction writer.

My arms hurt when I remember all that grinding and polishing..

Also see the great books Amateur Telescope Making!

Dave

[DragonLensmanWV]

[QUOTE=CEO;353280]My Dad made me and my friends build our own telescopes completely by hand by grinding and polishing our own glass all the way from 3" coasters for furniture to 24" telescopes. One interesting side note, one of the neighborhood kids who we built telescopes with was David Brin...who became astrophysicist and Hugo Award Science fiction writer.

My arms hurt when I remember all that grinding and polishing..

Also see the great books Amateur Telescope Making!


Yes, I've read several of Brin's works. Geez, looking at his site I have a lot of catching up to do.

My grandfather hand ground his own 12" reflector lens and built his telescope from that. The tube must have been 6 feet long. I remember he had it installed in his back yard in a concrete base and attached a star drive to it so it would track whatever you were looking at. You could see the different colors in the rings of Saturn. Quite heady stuff for a grade school kid back then.