Is building a Dobsonian worth it?
Building your own Dobsonian is a popular project because the design is simple: a mirror, a tube and a rotating wooden base. Dobsonians were originally promoted as telescopes that ordinary people could build with inexpensive materials. A home build can save money, particularly on large apertures, and gives you a telescope you understand fully. It also takes time and some basic woodworking.
If you have not used a telescope before, consider reading our beginner’s guide to Dobsonians first, and perhaps observing through a commercial one to learn what you want from the design.
The main parts
- Primary mirror: the large concave mirror that collects light.
- Secondary mirror: a small flat mirror near the top of the tube that redirects light to the eyepiece.
- Mirror cell: a support that holds the primary and allows it to be tilted for collimation.
- Optical tube: the structure that keeps the mirrors in line.
- Focuser: the part that holds the eyepiece and moves it in and out.
- Finder: a red-dot or small optical finder for aiming.
- Rocker box and ground board: the wooden base that allows altitude and azimuth movement.
Optics: buy or make
The mirror is the key decision. You can:
- Buy a ready-made mirror set (primary and secondary) from an optics supplier. This is the simplest route and gives predictable results.
- Buy a mirror kit and finish it yourself.
- Grind and polish your own mirror. This is a long, rewarding craft in itself and is described in how to make a telescope mirror.
Most first-time builders buy the optics and put their effort into the tube and mount.
Tube options
- Solid tube: often made from heavy cardboard concrete-form tube, plywood or other materials. It is simple and keeps stray light out.
- Truss tube: an open design with poles connecting the mirror box to the upper cage. It breaks down for transport and suits larger apertures, but needs a light shroud and more careful design.
The focal length of the mirror determines the tube length, so decide on the optics before cutting the tube.
Rocker box and bearings
The classic base is a plywood box with side bearings that cradle the tube and a ground board that lets it rotate. Smooth motion comes from low-friction Teflon (PTFE) pads running on a smooth laminate surface. Balance is important. The tube should stay where you point it, and the friction should be adjustable. Many published plans address the geometry of the bearings, so follow a well-tested plan, such as those from Stellafane, rather than inventing dimensions.
Focuser, finder and mirror cell
Many builders buy a ready-made focuser and finder, because these are fiddly to make well. A good mirror cell has three adjustable points for collimation and a support system that holds the mirror without pinching it. Both the cell and the focuser must be firmly mounted, as any flex will affect alignment.
Build order
- Choose the aperture and mirror focal length.
- Obtain or make the optics.
- Design the tube length and diameter around the mirror and focuser.
- Build the mirror cell and the upper end.
- Build the rocker box and ground board.
- Paint the inside of the tube matte black.
- Assemble, balance and test the motion.
- Collimate and test on the Moon or a bright star.
First light and collimation
After assembly, the mirrors need aligning. Our guide to using a Dobsonian telescope explains the basic collimation process and how to set up for observing.
Common mistakes
- Choosing a very large aperture for a first build.
- Cutting the tube before confirming the mirror’s focal length.
- Using stiff or weak materials that flex.
- Skipping the baffling or a matte finish inside the tube.
- Underestimating how heavy the finished scope will be.
FAQ
How hard is it to make a Dobsonian telescope?
With purchased optics and basic woodworking skills, it is a manageable project for many people. Making the mirror yourself adds a great deal of time and care.
Should I build or buy?
Buying is faster and often cost-competitive at smaller sizes. Building tends to make more sense for large apertures or if you enjoy the process itself. Our best Dobsonian telescopes guide helps if you decide to buy.