This lens features a so far unachieved correction of chromatic aberrations. The secondary spectrum which is the dominating aberration of lenses of long focal length has been corrected for the entire spectral range between approx. 400 and 1000 nm. Visual focusing in visible light guarantees optimum sharpness even on IR or false-color film. It's ideal for taking photographs which are to be considerably re-enlarged and is primarily applied in technical and scientific IR photography. Special effects in landscape and architectural photography, geology, hydrology and archaeological documentation with the aid of aerial photographs, botany, plant pathology, environmental control and multispectral photography are examples of the wide range of application of this extraordinary lens. As the focusing ring has no infintity-stop position, focusinf for long range work must also be performed using the camera's focusing screen.