An image pickup apparatus includes an objective optical system, an image pickup element having a surface at an image formed by the objective optical system, and an etalon positioned between the objective optical system and the surface of the image pickup element. The etalon includes a gap, an optical path length of which is controllable for scanning the wavelengths transmitted by the etalon to thereby select the wavelengths that reach the surface. An optical filter is positioned between the objective optical system and the surface and has a first wavelength range over which incident light is reflected, a second wavelength range over which incident light is transmitted, and a boundary wavelength range that is bounded by the first and second wavelength ranges. The boundary wavelength range lies entirely within the wavelength range the peak transmission of the etalon can be scanned. A method of calibrating the etalon is also disclosed.