In photography, a close-up lens is a secondary lens used to enable macro photography without requiring a specialized primary lens. Closeup lenses enable the use of more advanced cameras to take photos closer to a subject without the need for a dedicated macro lens.
Close-up lenses work like reading glasses, allowing a primary lens to focus more closely. Bringing the focus closer allows the photographer more possibilities.
Close-up lenses typically mount on the filter thread of the primary lens and are often manufactured and sold by suppliers of photographic filters. Nonetheless, they are lenses and not filters. Some manufacturers refer to their close-up lenses as diopters, after the unit of measurement of their optical power.
A close-up lens does not affect exposure, unlike extension tubes, which also can be used for macro photography with a non-macro lens.
Close-up lenses can make a telephoto lens function as a macro lens with a large working distance. This is useful, for example, to prevent scaring small animals or isolating the subject from messy surroundings. To use the filters for animals the size of the animal will determine the working distance (small snakes 1 m to 50 cm, lizards 50–25 cm, small butterflies, beetles 25–10 cm), so it is essential to know what will be the favorite subject before screwing on a close-up lens. The close-up lenses are most effective with long focal length objectives and using a zoom lens is very practical to have some flexibility in the magnification. A good technique for sharp focussing is to take a picture at a long focal length first to have optimal sharpness at the essential details and then zooming out to have the desired size in the frame.
Some single-element close-up lenses produce images with severe aberrations but there are also high-quality close-up lenses composed as achromatic doublets which are capable of producing excellent images, with fairly low loss of sharpness.