Passage: In 1849, Rutherfurd abandoned his study of law to dedicate his leisure to science, particularly astronomy. He performed pioneering work in spectral analysis, and experimented with celestial photography. He invented instruments for his studies, including the micrometer for measuring photographs, a machine for producing improved ruled diffraction gratings, and the first telescope designed specifically for astrophotography.Using his instrumentation, Rutherfurd produced a quality collection of photographs of the Sun, Moon, and planets, as well as star clusters and stars down to the fifth magnitude. In 1862, he began making spectroscopic studies using his new diffraction grating. He noticed distinct categories of spectral classes of stars, which Angelo Secchi expanded upon in 1867 to list a set of four stellar classes.Rutherfurd served as a trustee of the Columbia University from 1858 until 1884, and donated his photographs to that institution.In 1873, then President Ulysses S. Grant appointed Rutherfurd one of the scientific commission to attend the Vienna Exposition, however, he declined the honor due to previous business engagements in the United States.  In 1884, he was named by President Chester A. Arthur as one of the delegates to the International Meridian Conference which met in Washington in October, 1885.He was one of the original members of the National Academy of Sciences created in 1863, and was an associate of the Royal Astronomical Society.

Question: Rutherford took his interest of astronomy and experimented with what?
celestial photography