A multi-spectrum, multi-channel imaging spectrometer includes two or more input slits or other light input devices, one for each of two or more input channels. The input slits are vertically and horizontally displaced, with respect to each other. The vertical displacements cause spectra from the two channels to be vertically displaced, with respect to each other, on a single image sensor on a stationary image plane. The horizontal displacements cause incident light beams from the respective input channels to strike a convex grating at different respective incidence angles and produce separate spectra having different respective spectral ranges. A retroflective spectrometer includes a convex grating that, by diffraction, disperses wavelengths of light at different angles and orders approximately back along an incident light beam. A single concave mirror reflects both the input channel and the dispersed spectrum. A prism, set of mirrors, beam splitters or other optical element(s) folds the input channel(s) of a spectrometer to enable the input(s) to be moved away from the plane of the image sensor, thereby enabling a large camera or other device to be attached to the spectrometer without blocking the input(s). A mounting mechanism enables a curved optical element to be adjusted through lateral and transverse translations, without requiring a gimbal mount.