An optical system including: - at least one objective lens; - an optical filter; and - an imaging lens, or a first aperture array comprising a plurality of aperture elements; and wherein the at least one objective lens, the optical filter, and the imaging lens or first aperture array are arranged along an optical axis to form at least one projection of the optical filter on the imaging lens or on the first aperture array, characterized in that the optical system further includes a filter selection means for selecting filtered electromagnetic radiation to be provided to the imaging lens or the first aperture array; and in that the at least one objective lens is located at a position upstream from the first aperture array or the imaging lens and the optical filter and the filter selection means are located at a position upstream from the at least one objective lens so that the first aperture array or the imaging lens images an object located upstream of the objective lens onto an image sensor plane to provide at least one or a plurality of images of the object at the image sensor plane and so that the optical filter is imaged by the objective lens onto at least a part of the first aperture array or the imaging lens to filter the at least one or the plurality of images of the object as if the optical filter was physically placed in contact with the first aperture array or the imaging lens. - at least one objective lens; - an optical filter; and - an imaging lens, or a first aperture array comprising a plurality of aperture elements; and wherein the at least one objective lens, the optical filter, and the imaging lens or first aperture array are arranged along an optical axis to form at least one projection of the optical filter on the imaging lens or on the first aperture array, characterized in that the optical system further includes a filter selection means for selecting filtered electromagnetic radiation to be provided to the imaging lens or the first aperture array; and in that the at least one objective lens is located at a position upstream from the first aperture array or the imaging lens and the optical filter and the filter selection means are located at a position upstream from the at least one objective lens so that the first aperture array or the imaging lens images an object located upstream of the objective lens onto an image sensor plane to provide at least one or a plurality of images of the object at the image sensor plane and so that the optical filter is imaged by the objective lens onto at least a part of the first aperture array or the imaging lens to filter the at least one or the plurality of images of the object as if the optical filter was physically placed in contact with the first aperture array or the imaging lens. and wherein the at least one objective lens, the optical filter, and the imaging lens or first aperture array are arranged along an optical axis to form at least one projection of the optical filter on the imaging lens or on the first aperture array, characterized in that the optical system further includes a filter selection means for selecting filtered electromagnetic radiation to be provided to the imaging lens or the first aperture array; and in that the at least one objective lens is located at a position upstream from the first aperture array or the imaging lens and the optical filter and the filter selection means are located at a position upstream from the at least one objective lens so that the first aperture array or the imaging lens images an object located upstream of the objective lens onto an image sensor plane to provide at least one or a plurality of images of the object at the image sensor plane and so that the optical filter is imaged by the objective lens onto at least a part of the first aperture array or the imaging lens to filter the at least one or the plurality of images of the object as if the optical filter was physically placed in contact with the first aperture array or the imaging lens.