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Telescopes started out as a playground accident; the spectacle-maker's children played with some discarded lenses and by chance hit upon a combination of lenses that made distant objects look close. Within a few years word of the discovery spread to Italy, where an ambitious scientist, one Galileo Galilei, turned an ''optic tube'' skyward and started a major revolution in astronomy.

Too few of us play with lenses anymore. We prefer to buy ready-made telescopes and computerized cameras and then carefully follow the directions for their use instead of experimenting with bits and pieces of optical equipment and learning from our experiments.

Here are some simple ideas for things you can make and do with lenses, things you can really enjoy trying. There's something here for any curious person - a beginner, an old pro, or someone somewhere in between. The optics may be surplus, obsolete, or gathering dust in your closet or camera bag. Obsolete junk has one big advantage: it's really cheap. Break out the junk and start experimenting! And don't be surprised if some of these crazy ideas become a permanent part of your stock of astronomical equipment.

Start off by dredging up that old 8mm movie camera, the old kind with a screw-in lens. Remember that relic from the days before home video? If you find an old camera with a three-lens turret, you're in luck, but the really obsolete, non-Super-8, know-nothing camera is perfect. These usually bring a couple of dollars at yard sales.

Why search for these ancient 8mm cameras? The answer is simple; the lens, used backwards, makes a very acceptable eyepiece. A normal lens for such cameras is roughly 13mm focal length at f/2. The aperture is around 7mm in diameter when fully open. The lenses are high-quality, highly color-corrected formulas designed to put images on 8mm film that will be blown up to wall size. It's relatively easy to make good-quality glass lenses in such small sizes. Even so, the original lens often costs a substantial sum, especially when converted into today's dollars. Because they're obsolete, they're a real bargain.

Do you have an old 2.4 inch refractor? You know, the same kind you saw being sold as a ''Comet Clobberer'' during the Halley craze but is twenty years old? Try this; compare the 8mm movie camera lens to your economy 0.965'' eyepiece. The first time I did this I was amazed. The movie camera lens gave greater sharpness and clarity than the eyepiece did, and it hadn't cost me a cent. Most of the old color fringeing was gone too. So, for a couple of bucks at most, you'll have an amazingly good quality eyepiece. Your old ''Comet Clobberer'', equipped with its obsolete 8mm camera lens, now turns out to be a nice scope. You might even feel the urge to start using it again. Sure, I know a standard eyepiece might be even better, but try finding one for the cost of a burger.

To make your junk-box eyepiece more permanent, use some metal or plastic tubing, epoxy, black paint, a black cardboard stop (optional), and voila - you've just built your own experimental eyepiece. It may even become your favorite.

Now let's try building a telescope. What can you use for an objective lens? We need a good magnification ratio, and a fair amount of ''glass'' area would add to its appeal. Low cost is essential too. Where can you find such a beast? Enter the photographer's screw-in diopter lens set. These were used for close-up photography before macro-zoom lenses were invented. Millions of diopter lens sets are lying around gathering dust - inconvenient and ''obsolete''. (There's that magic word again!) Practically any such lens will do for experiments - we aren't particular. Any filter size is fine too. So what if the lens was made for an Exacta camera? The larger the glass area the better. One or two dollars per lens seems to be the going price in stores and ads, which really isn't bad for a 50mm diameter lens with a focal length of 1000mm. The camera store will call it a +1 diopter lens.

At the hardware store pick up a 1-meter length of 2-inch diameter PVC pipe for the tube, a pipe coupler to serve as a lens retaining ring and dew cap, and a 2'' to 1'' coupler to hold your 8mm movie camera lens eyepiece. The magnification will be 1000mm/13mm, or about 80X. Assemble it and you have built yourself a fun telescope. It's about twice as powerful as the one Galileo used and probably better optically. For $10 you can afford to let this scope take a beating (translation: it's a perfect project scope for kids). Or would you rather they play with yours?

Want low magnification? You can get it by using a longer focus eyepiece or a shorter focus objective. Will the 50mm lens from that decrepit SLR your brother-in-law dropped in the lake (and you fished out) fit the bill? The camera doesn't work anymore, so try the lens. What can you lose? If it works, you'll get 1000mm/50mm, or 20X.

If you buy a three-lens close-up kit, you can build quite a variety of scopes. Get the clerk in your favorite camera store to dig around in that box of stuff the store couldn't sell the last time it held an 80 percent off sale. Aha, here they are - three closeup lenses for $8.95. Offer him $5. Note that the focal length of diopter-rated close-up lenses is 1000mm divided by the strength of the lens in diopters, so a lens rated +2 diopters has a focal length of 1000mm/2, or 500mm. With one eyepiece coupler unit and three lens-and-tube sections you can make three scopes for about $15, or $5 each.

These scopes will have magnifications from 15X to 80X, a nice complement to the magnification you can get with your primary scope but beyond that of ordinary binoculars. You should be able to see craters on the Moon, the phases of Venus, the ovalness of Saturn (if not its ring system), Jupiter's disk and satellites, hundreds of double stars, and dozens of deep sky objects.

Optically, though, diopter lenses leave quite a bit to be desired, especially in terms of color correction. More obsolete junk to the rescue. Unearth that 135mm f/2.8 telephoto lens you don't use anymore. It's a high quality, well color-corrected optical assembly. Set it to infinity and attach it to your 8mm move camera eyepiece lens. How? Mount the eyepiece on a rear lens cap, preferably the older metal style.

Drill out a central hole and epoxy in an appropriate bit of PVC pipe or metal tubing. Blacken the inside with flat black spray paint. Plug in your ''eyepiece'' and set the focus; you've got a nice 10x40mm finder with excellent optics.

For really low magnification dig out that 50mm normal lens, attach your eyepiece to it, and you've got a dandy 4x finder. This is an especially satisfying way to recycle old screw mount thread camera lenses in today's bayonet-mount world. Radio antenna clamps and muffler clamps are a big help in mounting such finders on a telescope, though you may well think up something better. Be creative.

A 200mm f/4 camera lens gives you a nice 16x scope with a respectable 50mm aperture. Since virtually any lens from any camera will work, feel free to experiment. Haunt flea markets. Visit a few pawn shops. Poke around a surplus store. Scrounge from your photographer friends. Take your junk to a swap meet and see if you can trade it for somebody else's junk. Discovery is a thrill.

Once you've built a couple of telescopes and spotting scopes, you may want to investigate making a few more eyepieces. Lenses for 16mm movie cameras were frequently traded in for zoom lenses. Many are gathering dust in camera store with prices around $10. Typically these are f/2 or faster 25mm lenses. They are high quality, highly color corrected, and quite a bargain. Any design we've mentioned for an 8mm movie lens ought to work with a 16mm camera lens - and the price is just a few dollars more. Again, have fun experimenting with all of them!

If you don't have a nice loupe for examining those tiny, millimeter-size astro images on your slides, you can make one. Cut the sides out of a 2'' to 1'' PVC pipe adapter to form a little tripod and slide your movie camera eyepiece in. A lens mounted in a coupler can be used directly on a light table.

Experiment with whatever optics you can find around the house, in the attic and closets, and in neighborhood garage sales. Sure, you'll find stuff you'll never use. But you might also turn up a real winner for just a few bucks.

If you're an old pro, here's your reward for browsing through this article. These 8mm and 16mm lenses are superb copy lenses for making one-step duplicates of astronomical slides. Construction is simple; remove your present lens from its bellows or extension tubes. Mount the 8mm movie lens on a camera body cap over the bellows with the inner surface of the lens facing out.

Using this rig is easy. Place a slide on a light table and use standard bellows focusing techniques. You can blow up an astrophoto 500 to 2,000 percent with crisp definition, good contrast, and excellent color fidelity. Try it. You probably already have the lens. Even if you don't, all you have to lose is a couple of dollars. I predict you'll be pleased with your bargain bellows enlarging lens, especially after you price an equivalent bellows lens. What you save in cold cash will please you even more.

If you're a serious astrophotographer, consider using an 8mm or 16mm movie lens for eyepiece-projection photography. Those lenses were designed to project super-sharp images on tiny film, and they work beautifully in reverse for enlarging tiny planetary images. You can use them in a commercial eyepiece-projection rig or put together something of your own.

The telescopes you build with obsolete optics may not be world-class creations. They may be a bit wiggly around the edges or show somewhat more chromatic aberration than you'd like. But you've gained something you couldn't get in a store-bought scope: the fun of doing. Try whatever lenses you can find and experiment with different combinations. So what if the images are a bit fuzzy? You'll learn how telescopes work, and why.

Use these cheap but good-quality scopes as gifts for the kids or as ideas for the budding astronomer. One final thought; when you've done your thing with them, don't put them back in the junk box. Pass your creations on to some of the neighborhood kids. Give them a chance to learn and play too. It's only fair. After all, aren't kids the ones who invented telescopes in the first place?

Date: 5 Apr 2000
From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Newsgroups: sci.space.history,sci.astro
Subject: Did The Vikings Make The First Telescope?

Did the Vikings make a telescope?
By Dr David Whitehouse
BBC News
April 5, 2000

The Vikings could have been using a telescope hundreds of years before Dutch spectacle makers supposedly invented the device in the late 16th century.

This remarkable possibility has emerged from a study of sophisticated lenses just recognised from a Viking site on the island of Gotland in the Baltic Sea. They were initially thought to be merely ornaments.

"It seems that the elliptical lens design was invented much earlier that we thought and then the knowledge was lost," says Dr Olaf Schmidt, of Aalen University in Germany.

Full story here:

http://news.bbc.co.uk/hi/english/sci/tech/newsid_702000/702478.stm