Patent ID: 8873046

Claim:
A spectroscopic detection device comprising: a stop in which an aperture is formed and on which detection light is incident; a first photodetector which detects the detection light; a second photodetector which detects the detection light; a collimator which converts the detection light emitted from the stop into substantially parallel light, and emits light to at least one of the first photodetector and the second photodetector; a dispersive element which is arranged between the collimator and the first photodetector, and disperses the detection light; a condensing optical system which condenses the detection light dispersed by the dispersive element to the first photodetector; and a wavelength selection filter which is arranged between the collimator and the second photodetector, and allows light in a specified wavelength range to enter the second photodetector, wherein: the collimator is configured so that a focal length for the detection light emitted to the first photodetector is longer than a focal length for the detection light emitted to the second photodetector, the collimator comprises: an optical path forming device which leads the detection light to at least one of the first photodetector and the second photodetector; a collimator lens which is arranged between the optical path forming device and the stop, and converts the detection light which has passed through the stop into substantially parallel light; and a variable magnification optical system which is arranged between the optical path forming device and the first photodetector, and changes a luminous flux diameter of the detection light as substantially parallel light which has passed through the optical path forming device; and a focal length of the collimator lens is shorter than a combined focal length of the collimator lens and the variable magnification optical system.