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[2]:

M=250f.

## See also

* Optometry
* Far point
* Snellen chart
* Visual perception
* Visual impairment

## References

1. ↑ Katz, Milton (August 1996). "Convergence Demands by Spectacle Magnifiers" (in en-US). Optometry and Vision Science 73 (8): 540–545. doi:10.1097/00006324-199608000-00004. ISSN 1538-9235. PMID 8869985. https://journals.lww.com/optvissci/Abstract/1996/08000/Convergence_Demands_by_Spectacle_Magnifiers.4.aspx.
2. ↑ Pedrotti, Frank L.; Pedrotti, Leno S. (1996). Introduction to optics. Prentice-Hall international editions (2. ed., [Nachdr.] ed.). Englewood Cliffs, NJ: Prentice-Hall International. pp. 131. ISBN 978-0-13-016973-0.

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