As indicated by the designation "S", the 120mm S-Planar is a special-purpose lens. In contrast to most lenses, where optimum correction is found at long lens-to-object distances, the 120mm S-Planar is designed for use at short focusing ranges.

Its best performance is yielded at reproduction ratios from 1:10 to 1:2. Maximum correction is obtained at f/11. At this f/stop the modulation transfer factor in the center of the field is close to the value for an ideal field in a perfect optical system.

The S-Planar has been designed to satisfy the very high quality requirements of line-copy-work and technical photography calling for superior resolution and distortion correction. The 120mm S-Planar also differs from most normal lenses by having correction relatively insensitive to changes in image scale. It can therefore be used for long lens-to-object distances with excellent results but should then be stopped down somewhat more than is the case for a normal lens whose optimum correction is for long lens-to-object distances. The corresponding also applies for extremely short focusing distances and scales, only attainable with a bellows extension or extension tubes. At a lens-to-object distance of 5 ft, the scale of reproduction without extension tubes is 1:10; the lens is at its best here. The closest focusing point for the lens is 3 ft (0.95 m), corresponding to a scale of 1:5.8. The frequently fascinating range of scales between 1:12 and 1:4 can be covered with the extension tube 10.

The combination of a 120mm S-Planar and the Hasselblad extension bellows yields reproduction ratios between 1:1.9 (a reduction of approximately 2 times) and 0.55:1, corresponding to an enlargement of about 1.8 times. Those examples show that the lens is suitable both for applications calling for outstanding distortion correction and for a wide variety of assignments at relatively short lens-to-object distances. This lens is also suitable for most applications in industrial and advertising photography.