Close-up lens

They work like reading glasses, allowing a primary lens to focus more closely.

Some manufacturers refer to their close-up lenses as diopters, after the unit of measurement of their optical power.

Close-up lenses do not affect exposure, unlike extension tubes, which also can be used for macro photography with a non-macro lens.

[4] Close-up lenses are often specified by their optical power in diopters, the reciprocal of the focal length in meters.

For a close-up lens, the diopter value is positive: the bigger the number, the greater the effective magnification.

Higher quality achromatic lenses commonly lack a strength specification in diopters.

Close-up lenses change both the maximum and minimum focus distances of a lens.

This is useful, for example, to prevent scaring small animals or isolating the subject from messy surroundings.

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.

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.