Frequently Asked Questions (FAQ's)
Q: How much is this going to cost?
You can research this as well as I can. The primary mirror will be your greatest expense, followed by eyepiece(s), accessories (like a 1-power finder), and your diagonal mirror. Some prices (as of 1/26/1999) are as follows (prices do not include shipping):
Mirrors (Primary + Diagonal--from Coulter, as an example):
Eyepieces (from Orion):
One-Power Finder (from Rigel Systems):
Sonotube and other miscellaneous parts from these plans are incredibly inexpensive. A sheet of plywood will cost about $30 (but you will use less than 1/2 a sheet if you make a six-incher... maybe you can scrounge scrap material from a local cabinetmaker?
Remember: The San Francisco Sidewalk Astronomers have a long, proud tradition of helping folks make the least expensive/scrounged materials quality telescopes in the world!
There is nothing preventing you from spending more on your scope, however. A good commercial focuser can cost upwards of $100; a diagonal mirror holder and spider can cost $50, a commercial mirror cell can cost $30...
Q: What eyepiece(s) should I get, and what power will I get from them?
I recommend Plossl eyepieces like the Orion ones above--good eyepieces, not too expensive. Power is determined by dividing eyepiece focal length into the telescopes' focal length--in millimeters. Let's take a six inch f/8 telescope, for example: 6 X 25.4 (the number of millimeters per inch)=152.4mm. Multiply this by your focal ratio (f/8, for example)=1,219.2 mm. Divide a 26mm eyepiece into this and you get 46.89 power. Divide the same 1,219.2 mm by an eyepiece with a 10mm focal length and you get 121.9 power, right? These are good focal length eyepieces to start out with; one low power, and one medium power... You may want to add to your collection later.
Q: What will I be able to see?
Jupiter and Saturn will probably be smaller than you like (at the 121x example given above), but you will be surprised at how much detail you can see: Many cloud bands on Jupiter, not to mention the four Galilean moons, as well as the great Red Spot (which is more pale yellow nowadays); cloud bands on Saturn as well as its glorious rings and (most likely) Cassini's division--the most notable gap in the rings. The Moon will be extremely detailed. Star clusters, nebulae, and galaxies (invisible to the naked eye) will vary considerably in their glory and appearance. Do not forget to allow your scope to come to ambient temperature ("cool-down")--this is extremely important! Otherwise, excess turbulence within your scope will produce nothing but "blobs" at the eyepiece! Allow at least an hour for cool-down time. Sometimes, the "seeing" (upper atmosphere turbulence) never settles down, and you will be frustrated with the views all night... nothing to do but try another night!
Q: Is a ten-inch scope that much better than a six or eight?
Size does matter, but as is often said: the best telescope is one that is used the most often... A smaller telescope is easier to handle, to transport, and will (generally) be used more often. I very much like six-inch f/8 or f/10 scopes for use in light polluted cities: images of the planets and the Moon are stunning through quality scopes of this aperture. Eight-inchers of faster focal ratios (say f/5.6) are also very manageable with ordinary vehicles, and often visually outperform similar aperture commercial Schmidt-Cassegrains costing upwards of $2000! For ten-inchers, their aperture really comes into play at dark sites and with "deep-sky" objects. For this reason, especially if this is your first telescope, I recommend the smaller sizes unless you have ready access to dark skies, or know yourself to be a fanatic about this hobby already!
Q: How far away can I see with this size telescope?
The Sun is eight light minutes away; Jupiter a few hours; Saturn twice that distance; star clusters within our Milky Way are typically hundreds to thousands of light years away; galaxies are millions of light years distant, some billions... However, "How far away can I see?" is not really the question: The naked eye, for example, can see the Andromeda Galaxy which is 2.4 million light years away! Sure, any telescope will make the Andromeda clearer, and that is more to the point: The larger the diameter of the telescope, the more resolving power one has available to your eye/brain. Just as expensive computer monitors have more lines of resolution, and therefore display a more detailed image, a larger telescope mirror will collect more light and is therefore capable of higher magnification and higher resolution; enabling us to detect more detail in celestial objects.
Q: Will I be able to see color... anything like the beautiful space photographs I have seen?
No. We have all been spoiled by the Hubble Space Telescope, NASA, Star Trek and other beautiful space images--real or imagined. However, there is no substitute for seing the Universe as it really is through a telescope that you have made! I strongly suggest you attend a public "star party" in your locale and look through as many telescopes as you can. Go to http://www.skypub.com/ for an extensive listing of astronomy clubs--to find one in your area.
Q: Can I take photographs through this telescope?
No. Dobsonians can be made to track with computers or equatorial platforms, but at quite an expense... Even so, these set-ups are generally for visual use, not photographic. For photographing the sky through a telescope, I suggest a different kind of telescope, with a different kind of mount. Be prepared to spend at least $2000 on the telescope and another $2000 on photographic accessories. In short, you are on the wrong Webpage!
Q: How long will it take me to make this telescope?
Oh, about two weekends, I would guess. I think you will find most of your time spent at the beginning and end if your project: the gathering of the materials; and the final sanding, painting and finishing--everything else goes pretty fast--and is quite satisfying.
Q: Can I use a PVC (plastic) tube instead of a Sonutube (cardboard concrete forming tube)?
It has been done; but it is not recommended, for several reasons: PVC warps with heat (like in the back seat of a car on a hot day); PVC also warps with weight, adding to collimation problems. PVC is also quite heavy.
Q: Even the six-inch scope in your plans is a bit ambitious for me and my young child--is there someone that makes a kit in a smaller size?
I now have plans for a 4.5" on the site!
Q: Where can I get a printed copy of these plans?
If you can't print--for whatever reason--from these pages, I suggest you contact the Los Angeles Sidewalk Astronomers; last I heard, they are still sending out hard copies for $2.00 from this address:
The Sidewalk Astronomers
1946 Vedanta Place
Hollywood,
CA. 90068
If you are requesting these plans be mailed to another country, the price may be higher.
I do not send any plans through the mail, nor do I have any influence over those that do.