Description
Close-up lenses
In photography, a close-up lens (sometimes referred to as a close-up filter or a macro filter) is a simple secondary lens used to enable macro photography without requiring a specialised primary lens. They 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 dioptres 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 and split dioptre lenses
Main article: Close-up lens
A close-up lens is not technically a filter but an accessory lens that attaches to a lens like a filter, hence the alternative but misleading term “close-up filter”. Filter manufacturers often sell them as part of their product lines, using the same holders and attachment systems. A close-up lens is a single or two-element converging lens used for close-up and macro photography and works in the same way as spectacles used for reading. The insertion of a converging lens in front of the taking lens reduces the focal length of the combination.
Close-up lenses are usually specified by their optical power, the reciprocal of the focal length in meters. Several close-up lenses may be used in combination; the optical power of the combination is the sum of the optical powers of the component lenses; a set of lenses of +1, +2, and +4 dioptres can be combined to provide a range from +1 to +7 in steps of one.
A split dioptre has just a semi-circular half of a close-up lens in a standard filter holder. It can be used to photograph a close object and a much more distant background, with everything in sharp focus; with any non-split lens, the depth of field would be far too shallow.
