A two-channel spectrometer comprising: a first slit that receives a first portion of an incident beam and transmits a first slit output beam of a first wavelength range; a second slit that receives a second portion of the incident beam and transmits a second slit output beam of a second wavelength range, wherein the first and the second wavelength ranges are disjoint and well-separated, and wherein the first slit and the second slit are located at a common image plane; a first dispersive element and a second dispersive element; a beamsplitter; a shared double-pass all-reflective optical form that receives the first slit output beam and the second slit output beam, and has a reflective optical form output comprising a collimated output of the first portion of the incident beam and a collimated output of the second portion of the incident beam; a first imaging detector; and a second imaging detector; characterised in that, the beamsplitter upon which the reflective optical form output is incident separates the collimated output having the first wavelength range from the collimated output having the second wavelength range; the first dispersive element is optimised for the first wavelength range and receives from the beamsplitter the collimated output of the first portion of the incident beam from the all-reflective optical form and produces a first dispersed output, wherein the first dispersive element is oriented to direct the first dispersed output back through the shared double-pass reflective optical form to be incident upon a first location of the common image plane; the second dispersive element is optimised for the second wavelength range and receives from the beamsplitter the collimated output of the second portion of the incident beam from the all-reflective optical form and produces a second dispersed output, wherein the second dispersive element is oriented to direct the second dispersed output back through the shared double-pass reflective optical form to be incident upon a second location of the common image plane; the first imaging detector is at the first location of the common image plane; and the second imaging detector is at the second location of the common image plane; and the collimating-and-imaging functions of the shared double-pass all-reflective optical form are performed by reflective-only optics. a first slit that receives a first portion of an incident beam and transmits a first slit output beam of a first wavelength range; a second slit that receives a second portion of the incident beam and transmits a second slit output beam of a second wavelength range, wherein the first and the second wavelength ranges are disjoint and well-separated, and wherein the first slit and the second slit are located at a common image plane; a first dispersive element and a second dispersive element; a beamsplitter; a shared double-pass all-reflective optical form that receives the first slit output beam and the second slit output beam, and has a reflective optical form output comprising a collimated output of the first portion of the incident beam and a collimated output of the second portion of the incident beam; a first imaging detector; and a second imaging detector; characterised in that, the beamsplitter upon which the reflective optical form output is incident separates the collimated output having the first wavelength range from the collimated output having the second wavelength range; the first dispersive element is optimised for the first wavelength range and receives from the beamsplitter the collimated output of the first portion of the incident beam from the all-reflective optical form and produces a first dispersed output, wherein the first dispersive element is oriented to direct the first dispersed output back through the shared double-pass reflective optical form to be incident upon a first location of the common image plane; the second dispersive element is optimised for the second wavelength range and receives from the beamsplitter the collimated output of the second portion of the incident beam from the all-reflective optical form and produces a second dispersed output, wherein the second dispersive element is oriented to direct the second dispersed output back through the shared double-pass reflective optical form to be incident upon a second location of the common image plane; the first imaging detector is at the first location of the common image plane; and the second imaging detector is at the second location of the common image plane; and the collimating-and-imaging functions of the shared double-pass all-reflective optical form are performed by reflective-only optics.