Abstract: A variable spectral filter apparatus has a filter support rotatable about a single axis of rotation and has at least first and second transmissive spectral filters, each spectral filter having a filter width defined by its first and second edges, wherein the filter width is orthogonal to the axis. The first edges of the filters are equidistant from the axis of rotation when the filter support is rotated to any angle. The plane of each of the spectral filters is parallel to the axis. Rotational positions of the filter support about the axis of rotation, over a first 60 degree range of angles, define, between the first and second edges of at least the first spectral filter, an undeviated filtered light path of at least half the filter width that extends orthogonally with respect to the axis. A rotational actuator is energizable to rotate the filter support about the axis.

Abstract: A variable spectral filter apparatus has a filter support rotatable about a single axis of rotation and has at least first and second transmissive spectral filters, each spectral filter having a filter width defined by its first and second edges, wherein the filter width is orthogonal to the axis. The first edges of the filters are equidistant from the axis of rotation when the filter support is rotated to any angle. The plane of each of the spectral filters is parallel to the axis. Rotational positions of the filter support about the axis of rotation, over a first 60 degree range of angles, define, between the first and second edges of at least the first spectral filter, an undeviated filtered light path of at least half the filter width that extends orthogonally with respect to the axis. A rotational actuator is energizable to rotate the filter support about the axis.