The Apo-Sironar-S is a lens for universal use which has been optimized to provide the highest image reproduction quality. Its range of application usually goes from product and industrial photography to landscape and urban photography. Its special strength can be seen when complex, fine structures in the outer part of the image circle must be reproduced.
It provides an image angle of 75° and permits even more generous camera movements, than they are required for perspective correction in architectural and product photographs. Furthermore, the Apo-Sironar-S with a long focal length in relation to the image format, is ideal for the application as a “telephoto lens”, because of studio and technical cameras (if required with an additional bellows) permitting particularly large bellows extensions. Therefore problematic telephoto constructions with a barlow group, which tend to create color fringes and provide the advantage of short length only for use with cameras without bellows, are not necessary any more.
As a result of the elimination of the secondary spectrum thanks to the use of ED glass with anomalous dispersion (ED = extra low dispersion), no visible color fringing occurs even at edges with extremely high contrast. In addition, the light fall-off towards the image corners (vignetting) has been reduced for a more uniform illumination.
Thanks to this high optical performance in the edges of the field, the six-element Apo-Sironar-S can be used with a larger aperture (depending on the film format, e.g. f/16 instead of f/22) as its working aperture. This reduces diffraction and provides a special advantage for outdoor shots due to the higher shutter speed.