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Bandpass of a Spectrograph

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Bandpass of a Spectrograph

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With a spectrograph, the term bandpass refers to the entire wavelength range in the long strip output to the detector. Thus the bandpass in a spectrograph is very wide, limited only by the output aperture. However, it is not enough to simply remove the slit from a monochromator and use this larger aperture. Generally, wavelengths away from the center of a monochromator slit are focused slightly inside the instrument. Spectrographs are designed to correct this curvature; they have a flat output field matched to flat CCDs and PDAs.Very often, the length of the detector limits the bandpass. For example, the Oriel MS257 spectrograph has a 28 mm flat field. If this instrument is used with a CCD that is only 25.4 mm in length, the bandpass definition must keep this limitation in mind.

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