noun
A scientific instrument that records spectra, typically used in astronomy, chemistry, or physics.
天文学者は分光写真機を使って星の光を分析する。
Astronomers use a spectrograph to analyze starlight.
分光器 is a broader term for any spectrometer, while 分光写真機 specifically refers to a spectrograph that records spectra photographically or digitally.
Compound of 分光 (spectroscopy) + 写真 (photography) + 機 (machine). The exact historical derivation is uncertain, but the term follows standard technical word formation patterns.