# Dobsonian

Also called: Dob, truss Dobsonian.

A Newtonian reflector on a simple rocking-box mount — the easiest way to get a big aperture.

John Dobson popularised the design in the 1960s and 70s on San Francisco's sidewalks: a [Newtonian](https://astropilot.space/glossary/reflector) tube in a plywood box that swivels and tilts on Teflon pads. You point it by hand. It's simple, stable and cheap, so a Dobsonian puts 8, 12 or 16 inches of aperture within reach. Big ones break down into a truss of poles for transport.

Most are fast (f/4–f/6), so they show [coma](https://astropilot.space/glossary/coma) at the field edge and benefit from a [coma corrector](https://astropilot.space/glossary/coma-corrector); they don't [track](https://astropilot.space/glossary/tracking) the sky on their own.

**Related:** [Reflector](https://astropilot.space/glossary/reflector.md), [Coma corrector](https://astropilot.space/glossary/coma-corrector.md), [Mount](https://astropilot.space/glossary/mount.md), [Tracking](https://astropilot.space/glossary/tracking.md), [Star hopping](https://astropilot.space/glossary/star-hopping.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/dobsonian