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Telescope Building Frequently Asked Questions

How much will it cost?

There is not an easy answer for this question. Factors that determine cost include the size of the primary mirror, the quality of components used to make the mounting, and the quality of components like finders, focusers, etc. For example, the mount can be made from solid Oak or press board. A focuser can be made from plumbing parts for about $2. A very high quality commercial focuser can cost over $200. Materials you already have on hand and your ability to discover treasurers at junk yards can also be important. Here are some representative prices as of June 2002:

Telescope optical component kits are available from E-scopes . Prices for 6-8 inch telescopes range from $230 to $300

Pre-made mirrors from E-scopes (includes primary and secondary mirrors):

  • 4.5-inch, f/8 - $65.00
  • 6-inch, f/5 - $172
  • 8-inch, f4.5 - $240
  • 8-inch, f/6 - $240

Mirror grinding kits from Newport (includes glass for primary mirror, completed secondary mirror, polishing compounds, AND coating of the primary mirror when it is completed).

  • 4.5-inch - $67 to $73
  • 6-inch - $100 to $120
  • 8-inch - $150 to $170
  • 10-inch - $300 to $320

Make a spider for a few dollars or buy one for $30 to $40

Make a focuser for a few dollars or buy one for $30 to $75

Eye pieces will run ~$50 each from Orion. You will want a couple.

Bottom line -- if you buy a mirror grinding kit, make the base with plywood, buy a focuser, spider, and eye piece -- you should be able to make a nice 6 inch telescope for $300 to $400.

How long will it take?

Another difficult question. The answer depends more on you. First time builders have completed 10" telescopes in as little as two weekends. Others have been working their mirrors for 4 years. John Dobson and a couple of TAAS members built a 6" solar telescope from scratch in 1 day.

As a rule of thumb, first timers should figure approximately 20 hours to grind a mirror, 20 hours to polish it, and another 20-40 hours to build a mount (depends on wood working skills, access to tools, etc.)

What should I make?

The best advice here is to get out to a TAAS star party and try out different telescopes. Budget, where you live, and how you plan to transport the telescope are also important. The best telescope in the world is useless if it is too big to transport and stays in the house all the time.

Typical first time telescopes are in the 6 to 10 inch range with f-numbers in the f/6 to f/10 range

What is an f-number?

The f-number or f-ratio of a telescope is simply the ratio of its length to diameter. For example, an 8 inch telescope that is 56 inches long is 7 times longer than it is wide so it is an f/7. F-numbers are important. Telescopes with small f-numbers (below f/6) are more difficult to build. Telescopes with large f-numbers (above f/8) are easier to build but start becoming difficult to transport.

What will I be able to see?

Typical first time telescopes will show good detail of Jupiter and Saturn. The moon will be quite spectacular. Double stars and brighter nebula will look very nice. With practice, asteroids can be located and tracked. An inexpensive solar filter will turn your new telescope into a great solar telescope. The relatively small apertures will make "deep sky" observing difficult.

How far away can I see?

This is a common question that really does not make much sense. For example, the Andromedia Galaxy is approximately 3 million light years away but can be seen with the naked eye. Asteroids are light minutes away but cannot be seen without a telescope.

A better question is: How faint an object can I see and how much detail will I see?

The diameter of the primary mirror determines how much light can be captured and directed to your eye. The larger the mirror the fainter the object you can see. Resolution is also a function of primary mirror diameter. The larger the mirror the more detail a telescope will give.

How well an observer is trained is almost as important as telescope size. For example, a practiced observer will see more in a 6-inch telescope than a new observer will see in a 10-inch.

The best way to answer this question is to attend a star party and look at the same objects through different size telescopes. In any event, the views through a 6-10 inch telescope will be well worth the effort to build them.

How much "power" will my telescope have?

The magnification of a telescope is calculated by dividing the focal length of the mirror (or objective lense) by the focal length of the eye piece. For example, a telescope with a focal length of 100 inches used with an eye piece that has a focal length of 1/2 inch provides a magnification factor of 200. Note that the diameter of the mirror is not used to calculate magnification.

"Power" or magnification is generally the most misunderstood characteristic of a telescope. Department store telescopes often make claims of500 to 1000 "power" or magnification. While the figures are mathematically correct they are very misleading.

As stated above, the resolution of a telescope is a function of the mirror diameter. As the magnification is increased the resolving power of a telescope becomes more obvious. At some point, magnification simply makes an object get bigger and more fuzzy.

As a rule of thumb, the highest usable magnification a telescope can provide is 50 times the mirror diameter. A 6-inch telescope can therefore provide useful magnification of about 300. A 2-inch department store telescope can only provide 100 times useful magnification.

The atmosphere also plays an important role. On most nights, turbulence in the atmosphere will make operating a telescope (regardless of mirror diameter) at magnifications greater than 200-400 difficult.

Can a child or young adult make a telescope?

Age is not nearly as important as attention span and attention to detail. The physical strength required to make a 4.5-inch or 6-inch mirror is not great. Adult supervision should be provided while the mechanical components are being built since sharp tools will be required.

If a child or young adult can stay on task for several hours at a time and not loose interest a project that could take 60 hours of work then they should have no problem building a telescope.

Can I take pictures with my telescope?

Probably not. Most first time telescopes are constructed with Dobsonian mounts. The Dobsonian is a high performance and low cost mount but it does not not track objects as they move across the sky. Home made telescope mounts capable of tracking objects with the high precision needed for astrophotography are beyond the scope of most first timers. Commercial mounts will run several thousand dollars.

Is there a really easy way to build a small telescope?

Check out Stargazer Steve


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