[3][4] While a graduate student he began working at Sacramento Peak Observatory (SPO) in Sunspot, New Mexico, collecting data for his doctoral thesis.

[3] Dunn built a 38 cm (15 in) solar telescope equipped with a birefringent filter and a film camera for recording chromospheric spicules, which he used to collect data for his thesis.

[2] His drive to increase the resolution of observations to see finer solar details defined the rest of his career.

[2] In 1976–1977 Dunn served as acting director of Sacramento Peak Observatory during its transition from being operated by the Air Force Cambridge Research Laboratories to the National Science Foundation.

[7] In 1998 Dunn was awarded the George Ellery Hale Prize of the American Astronomical Society for his "bold and imaginative innovation of instrumentation for solar physics, his discovery of important new phenomena on the Sun, and the impact of his contributions on solar physicists worldwide.

[2][9] The rededication plaque describes Dunn as "one of solar astronomy's most creative instrument builders" and the telescope as his "masterpiece",[10]