Kinoforms long focal objectives for astronomy

A new class of long focal apochromatic optical systems is described which permits the formation of images in different spectral ranges. The systems are composed of kinoform elements combined with conventional optical elements. The correction of monochromatic and chromatic aberrations is discussed theoretically with respect to their occurrence in long-focal, large-f-number astronomical lenses. Kinoform elements are compared to traditional optical elements, and the synthesis of long focal apochromats is shown to be possible with kinoform elements and typical optics. A discussion of diffraction efficiency and spectral selectivity in kinoform elements shows that acceptable characteristics for these optics can be achieved over a wide spectral range. Kinoform element objectives can be applied to high-resolution refractors, stellar sensors, large-telescope guiders, and collimators. The apochromatic lenses based on kinoform elements weigh 30-40 percent less than traditional lenses and offer high correction of chromatic aberrations, low thermal sensitivity, and a minor augmentation of stray light.