The imaging, especially of small objects which fill the frame as much as possible is the source of problems for the usual lenses (which are optimized for the distance range of infinity). Even normal lenses in 35 mm cameras permit a distance close up of only about 40 cm. That overwhelms subjects of a postcard size. One can get closer with especially calibrated macro lenses or with extension rings. Both possibilities are expensive, require greater light exposure, and take up additional space in the camera bag. For digital cameras, because of their built-in optical features, neither variant is realistic. As an alternative, there remains the use of close-up lenses and/or supplementary lenses.

Moreover, B+W close-up lenses are in comparison less expensive, require less exposure time, and are, like filters, typically small and light in weight. They function in front of the lens as a collection lens, which reduces the focal length with the extension unchanged, but which enlarges the image scale which can be attained. An increase in the exposure time is not required. The imaging of small but delicate objects, like flowers, insects, coins, or postage stamps, is thus made simple.

There are B+W close-up lenses in six different magnifications, between +1 and +10 diopters. Up to two close-up lenses can be used in combination, in which case their refractive powers are added together. For example, the combination of a close-up lens 1 and one of 3 corresponds to a close-up lens 4. More than two close-up lenses should not be combined, because there is the danger of vignetting and the impairment of imaging performance. For optimal performance and sufficient depth of focus, the lens should be stopped down by as much as three aperture increments. The focusing takes place, even with a close-up lens, by looking through the viewfinder (in the case of single-lens reflex cameras) or by means of autofocus.