Least distance of distinct vision

The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.

In optometry, the least distance of distinct vision (LDDV) or the reference seeing distance (RSD) is the closest someone with "normal" vision (20/20 vision) can comfortably look at something.^[1] In other words, LDDV is the minimum comfortable distance between the naked human eye and a visible object.

The magnifying power (M) of a lens with focal length (f in millimeters) when viewed by the naked human eye can be calculated as:

{M}={\frac {250}{f}}.

References

^ Katz, Milton (August 1996). "Convergence Demands by Spectacle Magnifiers". Optometry and Vision Science. 73 (8): 540–545. doi:10.1097/00006324-199608000-00004. ISSN 1538-9235. PMID 8869985. S2CID 21041392.

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[1] Katz, Milton (August 1996). "Convergence Demands by Spectacle Magnifiers". Optometry and Vision Science. 73 (8): 540–545. doi:10.1097/00006324-199608000-00004. ISSN 1538-9235. PMID 8869985. S2CID 21041392.

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See also

References