The World's Simplest Telescope -- Now you can own one!

In this day and age of apochromatic telescopes and huge dobsoniam reflectors, it is doubly frustrating to have the economy go south as this one has. I amuse myself by glancing through the Surplus Shed catalog to find things to do on a very low budget as I am now retired. I recently ran across at item that allowed me to build a refractor telescope just about like the one Galileo had way back when. It was inexpensive enough so if it failed, there was little loss and my curiosity was satisfied. After all, what can one do with a 30mm or so non-achromatic refractor at 50 to 80 power? After some thought, I figured not much, but decided to give it a try.

I was quite surprised. So was Galileo....

The project centers upon Stock # PL1107, a 30mm lens of 1000mm focal length, (L8112 could also be substituted). There are some other lenses that could be used if one gets a cardboard or metal tube that has a different diameter. For my tube I chose an aluminum one 48 inches long from href="http://www.onlinemetals.com/index.cfm target="_blank">http://www.onlinemetals.com/index.cfm

I cut this to slightly less than 39.4" and used an eyepiece I had hanging around. Please note that I do not mention any sort of focuser, as an eyepiece can be held at the end of the tube to focus; you might like to shim it in place or arrange some sort of focuser of your own. Keep it simple! My telescope was placed on a window ledge; resting the tube on a stepladder for support worked as well and was less suspicious!

For those using a handy cardboard tube from around the house or one that they purchase, there are some other lenses for different tube diameters. They should work equally well; if not, they can be stopped down to 30mm. They are as follows:

L6377 or 6378, 34.5mm or so x 1000mm fl.

L4020 44.5mm x 800mm

L8084 39mm x 800mm

All these including the above lenses cost $4 to $5 each. Any of these lenses can be "mounted" with some masking tape along the lens rim to the appropriate diameter tube. Just be sure that the tube is cut squarely when the lens is attached.

Almost any eyepiece from Surplus Shed can be used; just check the appropriate search under eyepieces on the web page. Avoid eyepieces with focal lengths under 12.5 mm or 1/2 inch. A good starter eyepiece might be a 25mm or 1" focal length for 40 power; a 12.5mm would yield 80 power. Surplus Shed has more than enough selection. You might also be tempted by some 1.25" diameter eyepieces, Huygenian design, selling for $5.95. They are available in 20mm (stock #L2086) and 12.5mm (stock #L2019).

A word to the wise: Microscope eyepieces are perfectly useable as eyepiece type really doesn't matter. A microscope eyepiece marked "10x" has a focal length of 25mm; one marked "20x" has a focal length of 12.5mm. Eyepiece diameters, such as 24.5mm or 1.25" really don't factor in here.

So what did I see? I was shocked at the lack of color error that I would have anticipated. True, the image wasn't quite as perfect for color, but it was a whole lot better that I would have ever believed possible. The moon was quite detailed at all phases; Jupiter showed 4 satellites and Venus had a crescent at closest approach. I think I resolved the double star, Alberio.

It leads me to wonder why more wasn't discovered with Galileo's telescope. Of course, everything is always obvious after the discovery and hindsight is always 20-20, or better! But I can offer some insights after using my telescope. The powers I suggest are way beyond what is considered useable in a 30mm diameter telescope.

My opinion of why this works is that first, spherical aberration of the objective is not going to be ugly in a f/33 lens. Second, bad seeing effects are going to be hardly observable when the average air cell is 90mm or so and the diameter of this telescope is 30mm; rather than call this the Questar Effect, I think the Galileo Effect is most apt. Third, glass quality in 1610 was a chancy thing when it came to optical qualities. And the grinding and polishing techniques surely did not yield the quality we expect today, or even 200 years ago. Last and most of all, there were no designs in Galileo's time for eyepieces. Obviously! The telescope had just been put to astronomical use! The Galilean eyepiece was of extremely narrow field and if there had been eyepieces with 20 degree fields, they would have been considered to be extremely wide angle. Believe it or not....

This is a very worthwhile, instructive project for young and old. Try it and be amazed!

Ed Turco