Telescope

A Simple Guide On How To Build A Dobsonian Telescope At Home

Observing outer space provides information that is much beyond scientific facts. It places human life in the larger context of the universe. Among all concepts of science, astronomy is the most interesting one. A telescope is an astronomer’s principal tool. All of us want to see the stars and observe the dark skies but can’t do it due to the lack of a good telescope. But what if we teach you how to build a Dobsonian telescope at home? 

Develop an understanding of the equipment before you begin gaining insights on astronomy. Study the types, process of mounting, and the limitations of a telescope. A Dobsonian telescope is the perfect telescope for beginners and is also among the cheapest telescopes available today. 

How To Build A Dobsonian Telescope

Follow these simple steps to make a Dobsonian telescope at home:

1. Choose Focal Length And Aperture Size

The focal length and aperture size are the fundamental features of any telescope. These parameters influence its design and function. They are different for a reflector and a refractor telescope respectively. 

Once you select the aperture size and focal length, feed these details into a telescope design program. These programs are readily available online. Telescope design programs provide dimensions for the structure of the telescope, depending on the focal length and aperture size you choose. 

If you do not have access to a telescope design program, you can search for the ideal dimensions of a telescope as per your parameters in books such as Building a Sidewalk Telescope written by John Dobson. 

2. Buy The Equipment

When you obtain the design and dimensions, start purchasing equipment and tools for the construction. When John Dobson made the Dobsonian telescope for the first time, he used inexpensive and then readily available castaway construction material.

People who build these telescopes today feel that sturdy equipment for the Dobsonian telescope is difficult to find. You can check your local hardware shops for these items. 

The items you will require to construct a Dobsonian telescope are: 

  • Mirrors
  • Nuts and bolts
  • Sonotube- It is a plywood tube that serves as the optical tube of the Dobsonian telescope
  • Telrad base
  • Focuser
  • Woodworking hand tools
  • Ebony star strips
  • Teflon
  • Adhesive
  • Electric drill
  • Plywood

3. Construction Of The Optical Tube

Most people face difficulty in finding the sonotube at hardware shops. For this reason, they construct an optical tube themselves. For a Dobsonian telescope, making an optical tube is simple. You need to cut and arrange pieces of wood in an octagonal manner. This structure provides more support and directs the light straight onto the mirrors and lenses.

Once you have cut the octagonal wooden structures, attach them to plywood and then design the tube as per the program. 

4. Mounting The Focuser

Once the optical tube is ready, mount the focuser on it. The focuser converges the light inside the optical tube. 

Follow these steps to mount the focuser on the optical tube:

  1. Calculate the diameter of the base of the focuser. It should be according to the dimensions of the aperture size and focal length. 
  2. Check the telescope design program for drilling a hole in the optical tube where the focuser will fit in. 
  3. Now drill a hole, which has a larger diameter than the base of the focuser. Place the focuser in this hole and mark positions for nuts and bolts. 
  4. Drill holes on these markings for the bolts. 
  5. Now set the focuser inside the hole permanently and tighten the bolts. 

5. Fix The Primary Mirror 

Professionals who have the resources and experience prefer to make their mirrors and lenses themselves. However, if you do not know how to grind lenses and mirrors for a telescope, you can buy them from the market or online platforms. 

In any telescope design program, a separate mirror cell is available. After purchasing mirrors and lenses, fix the primary mirror in the mirror cell. The mirror cell holds the primary mirror steadily inside the optical tube. 

While fixing the primary mirror in the mirror cell, place the mirror gently so that no optical distortions occur. Even the slightest movements can distort the primary mirror. It affects the image seen in the telescope. 

As a rule, the primary mirror in the mirror cell should not move more than 1/16th of an inch. In some designs, the mirror cell has retainer clips. You can tighten the clips as soon as you fix the primary mirror inside the mirror cell to allow minimum movement. 

If retainer clips are not available, you can purchase silicone adhesives for attaching the mirror. 

Fix the mirror in front of the optical tube. Use plywood as the mounting material and attach the mirror cell to it with silicone adhesive. Reinforce the silicone adhesive with collimation bolts. These bolts secure the mirror cell during the collimation of the telescope. 

6. Mount The Secondary Mirror

The next step is to mount the secondary mirror on a holder. It is a diagonal mirror readily available in the market. The holder for a secondary mirror is called the spider. 

For mounting the secondary mirror on the spider, you can use the same plywood mounting as before. Otherwise, a holder with a shell and a rim will also do the job. 

In case you use a holder, gently put the secondary mirror into its shell. Then press the mirror using medical cotton  to fit it into the rim of the holder. Just like fixing the primary mirror, avoid using force. It prevents optical distortions. 

Tip- If you use the same plywood mounting with silicone adhesives, then try fixing toothpicks between the mirror and the spider. Once the silicone adhesive has dried, remove the toothpick. It creates a space that ensures optimum movement of the secondary mirror. 

Follow these steps to mount the secondary mirror and the spider on the optical tube:

  1. Ensure a half-inch adjustment gap for the holder. 
  2. Check for the shortest distance between the base of the holder and the mirror. 
  3. Next, measure the longest distance between the base of the holder and the mirror. 
  4. Add these two values and divide them by 2. 
  5. Calculate the distance between the mounting hole on the spider and the base of the holder. 
  6. Add the measurements from steps four and five. 
  7. Next, measure the distance between the center of the focuser and the front of the optical tube. 
  8. Subtract the value in Step 6 from that in Step 7. It is the distance between the front of the optical tube and the mounting hole on the spider. It is the point where you have to mount the spider. 
  9. Drill the hole and mount the spider at this point.

7. Construction Of The Outer Structure

Construction of the mount requires carpentry work.  For making the telescope’s base, construct a simple box on which the optical tube holder can rest. 

For making the holder, construct a structure in which the optical tube can fit in comfortably. Make use of diameter bearings and rockers to make the holder adjustable. 

Cut out a round piece of plywood that will serve as the ground board. 

Conclusion

So, this is a simple guide for constructing a Dobsonian telescope. The simplicity of a Dobsonian mount and its reflector makes it easy to build at home. If you learn how to build a Dobsonian telescope, then you can construct other types of telescopes easily. 

All those who wish to enjoy the dark, rich, and starry skies, but cannot afford a high-resolution telescope, can follow these simple steps to construct a Dobsonian telescope at home.