Apo-Rodagon-D lenses are designed for the highest possible imaging quality for close-ups at just those scales around 1 : 1 where even the best enlarging lenses for larger scales begin to show their weak spots. Thus their typical application are transparency duplication, the preparation of internegatives and macro photography, where these lenses have an excellent performance for the recommended imaging scales. For the application on SLR cameras the Modular-Focus helical mount, available as an accessory, and a matching camera adapter are required. Furthermore, as well as for photography, they can also be used as high resolving optical systems for premium scanners.
The 6 elements, apochromatically corrected lenses feature high contrast and sharpness right up to the picture corners with virtually no color fringes. Distortion is corrected almost to zero and cannot be seen even in critical subjects with straight-lined structures parallel with the edges of the frame.
The optimum working aperture is between f/5.6 and f/8. This is worth mentioning because the effective aperture of a lens focused for a scale of about 1 : 1 is approximately two f-stops smaller than the nominal aperture. Therefore stopping down to smaller apertures than the nominal f/8 would result in visible blur because of diffraction.
All three models of the Apo-Rodagon-D are fitted with a practical click-stop aperture which can be disabled for stepless control and with pre-setting rings. These lenses are rather used for cameras and hardly for enlarging units and so there is no illumination of the f-number scale, because it only would have to be covered in order to avoid stray light.