A multi-channel imaging spectrometer comprising: a double pass reflective triplet optical subsystem configured to receive and collimate incident electromagnetic radiation and to provide a collimated output beam; at least one entrance slit configured to direct the incident electromagnetic radiation to the reflective triplet optical subsystem; at least one beamsplitter (140, 510) configured to receive the collimated output beam from the reflective triplet optical subsystem and to separate the collimated output beam into a plurality of spectral channels; at least two dispersive elements (150, 160, 530), each configured to receive and spectrally disperse a respective one of the plurality of spectral channels, the number of dispersive elements providing a corresponding number of dispersed outputs; wherein the at least one beamsplitter (140,510) is further configured to recombine the dispersed outputs and the reflective triplet optical subsystem is further configured to focus the plurality of dispersed outputs onto at least one focal plane co-located with the at least one entrance slit to produce an image from the plurality of dispersed outputs; wherein an image sensor is positioned at the at least one focal plane and optically coupled to the double pass reflective triplet optical subsystem; and wherein the number of dispersive elements (150, 160, 530) exceeds the number of focal planes; characterised in that the plurality of spectral channels includes at least three spectral channels, the at least one beamsplitter (140, 510) includes a first beamsplitter optically coupled to the reflective triplet optical subsystem and configured to separate the collimated output beam into a first spectral channel and a remaining wavelength range, and a second beamsplitter optically coupled to the first beamsplitter and configured to separate the remaining wavelength range into a second spectral channel and a third spectral channel; and wherein the at least two dispersive elements (150, 160, 530) include a first dispersive element configured to receive and spectrally disperse the first spectral channel, a second dispersive element configured to receive and spectrally disperse the second spectral channel, and a third dispersive element configured to receive and spectrally disperse the third spectral channel. a double pass reflective triplet optical subsystem configured to receive and collimate incident electromagnetic radiation and to provide a collimated output beam; at least one entrance slit configured to direct the incident electromagnetic radiation to the reflective triplet optical subsystem; at least one beamsplitter (140, 510) configured to receive the collimated output beam from the reflective triplet optical subsystem and to separate the collimated output beam into a plurality of spectral channels; at least two dispersive elements (150, 160, 530), each configured to receive and spectrally disperse a respective one of the plurality of spectral channels, the number of dispersive elements providing a corresponding number of dispersed outputs; wherein the at least one beamsplitter (140,510) is further configured to recombine the dispersed outputs and the reflective triplet optical subsystem is further configured to focus the plurality of dispersed outputs onto at least one focal plane co-located with the at least one entrance slit to produce an image from the plurality of dispersed outputs; wherein an image sensor is positioned at the at least one focal plane and optically coupled to the double pass reflective triplet optical subsystem; and wherein the number of dispersive elements (150, 160, 530) exceeds the number of focal planes; characterised in that the plurality of spectral channels includes at least three spectral channels, the at least one beamsplitter (140, 510) includes a first beamsplitter optically coupled to the reflective triplet optical subsystem and configured to separate the collimated output beam into a first spectral channel and a remaining wavelength range, and a second beamsplitter optically coupled to the first beamsplitter and configured to separate the remaining wavelength range into a second spectral channel and a third spectral channel; and wherein the at least two dispersive elements (150, 160, 530) include a first dispersive element configured to receive and spectrally disperse the first spectral channel, a second dispersive element configured to receive and spectrally disperse the second spectral channel, and a third dispersive element configured to receive and spectrally disperse the third spectral channel.