How to Build a Cheap Reflector Telescope

Written by kurt schanaman
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Build your own telescope, and gaze into the stars. Although today's reflector telescopes have become inexpensive, nothing speaks about your passion for the great beyond like having others congregating around your own custom-built telescope. If you have the time and the patience, anyone can procure the necessary items to produce a highly accurate Dobsonian reflector telescope.

Skill level:

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Things you need

  • Free plans downloaded from the non-profit San Francisco Sidewalk Astronomers club
  • Workspace at least 48 square feet
  • Tools:
  • Hammer
  • Saw
  • Drill and bit set
  • Tape measure
  • Compass
  • Screwdriver assortment
  • Nail set
  • Adjustable crescent wrench
  • Awl
  • 1-1/2 inch hole cutter
  • Carpenter's framing square

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    Gather Items

  1. 1

    Gather all of the tools and telescope items as listed by the San Franscisco Sidewalk Astronomers club in their plans at Neatly arrange your supplies along a wall in your workspace, sorted in the order that the instructions set forth.

  2. 2

    Cover the floor in your work area with plastic sheeting to prevent damage to the surface and to make cleanup a simple task when your project is completed.

  3. 3

    Connect a properly rated extension cord from a separate wall outlet to power your electric tools, making sure to route the cord so it isn't stepped on repeatedly, stumbled over or cut.

  4. 4

    Order the recommended telescope eyepieces, primary and secondary mirrors through your choice of mail-order outlet. When the large primary mirror arrives, don't remove it from the package until told to do so in the plan instructions, as this mirror is coated with a thin layer of reflective metal that is easily damaged.

    Assemble Your Telescope

  1. 1

    Calculate the f-stop needed for your telescope, and then apply the calculation to the length of the sonotube, cutting the tube to the precise focal length for your telescope.

  2. 2

    Build the mirror holder, secondary mirror spider (holder) and the mirror collimation adjustment frame.

  3. 3

    Drill the hole in your cardboard tube and attach the eyepiece holder tube.

  4. 4

    Glue the secondary mirror holder (spider) into the inside of the sonotube and align per the free open-source plans you've obtained from San Franscisco Sidewalk Astronomers club. Alignment of this mirror holder is critical to proper operation of your telescope.

  5. 5

    Paint the inside of the sonotube with the non-reflective flat-black paint and allow to dry thoroughly before continuing on with the addition of your primary mirror assembly on the bottom end of the sonotube.

    Attach Primary Mirror and Eyepiece

  1. 1

    Install the primary mirror into the collimation holder and fasten to the bottom end of the sonotube.

  2. 2

    Collimate (align) the primary mirror by adjusting the collimation screws on the primary mirror's holder until the round circle in the centre of the primary mirror is centred in the secondary mirror, which can be viewed through the eyepiece holder.

  3. 3

    Insert a low-power eyepiece into your homemade eyepiece holder on the telescope. Take the telescope outside during daylight and align the small finder scope to a distant object. Perform a final primary mirror collimation using that object as a reference.

  4. 4

    Set up your telescope outdoors approximately one hour before use so the mirrors stabilise with the outdoor temperature.

  5. 5

    Enjoy the new telescope you have built yourself, and don't forget to provide thanks to the San Francisco Sidewalk Astronomers club for making their plans freely available to the public!

Tips and warnings

  • Building a telescope requires a considerable amount of time-consuming tool work. The key is to take your time, working on your telescope just a couple of hours daily to ensure each step is completed to the best of your ability. The average time it takes to build such a telescope varies, although most are able to complete the task over a two-week period.
  • The large primary mirror you purchase for your telescope is easily scratched. Never allow anything abrasive to come into contact with your primary mirror, and keep the open end of your telescope tube covered when not in use to limit the amount of dust finding its way onto your primary mirror. Always follow the mirror manufacturer's cleaning instructions to prevent damage to the delicate mirror surface.

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