Definition of Focal length

1. Noun. The distance from a lens to its focus.

Exact synonyms: Focal Distance
Generic synonyms: Distance

Definition of Focal length

1. Noun. (optics) The distance at which something (e.g. a lens, mirror etc.) is in focus; in air it is the distance along the optical axis from a "principal plane" of the lens to one of the lens's focal points. ¹

¹ Source:

Medical Definition of Focal length

1. The distance from the optical centre of the lens to the focal point The focal length of an objective and its working distance are directly proportional. (05 Aug 1998)

Focal Length Pictures

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Lexicographical Neighbors of Focal Length

focal appendicitis
focal condensing osteitis
focal depth
focal depths
focal dermal hypoplasia
focal distance
focal embolic glomerulonephritis
focal epilepsy
focal epithelial hyperplasia
focal gallbladder wall thickening
focal gigantism
focal glomerulonephritis
focal illumination
focal infection
focal interval
focal length (current term)
focal lengths
focal lymphocytic thyroiditis
focal metastatic disease
focal motor seizure
focal necrosis
focal nephritis
focal nodular hyperplasia
focal plane
focal point
focal points
focal ratio
focal reaction
focal sclerosing glomerulopathy
focal sclerosis

Literary usage of Focal length

Below you will find example usage of this term as found in modern and/or classical literature:

1. The American Naturalist by American Society of Naturalists, Essex Institute (1871)
"TIIE focal length OF MICROSCOPIC OBJECTIVES. —Mr. CR Cross has ably discussed this subject in the "Franklin Journal." He remarks : "The investigation ot ..."

2. The Encyclopaedia Britannica: A Dictionary of Arts, Sciences and General (1890)
"The distance of Uie fir»t principal point from the first focal point is called the anterior focal length, and the term posterior focal length is applied to ..."

3. A Treatise on Light by Robert Alexander Houstoun (1915)
"Then, when the focal length is determined, the principal planes and nodal points can be found simply by measuring off their distances from the focal planes. ..."

4. The Standard Cyclopedia of Horticulture: A Discussion for the Amateur, and by Liberty Hyde Bailey (1916)
"For such size a rectilinear lens with a focal length of 7 or 8 inches is advisable; and if one of the two lenses forming the combination is available as an ..."

5. Publications of the Astronomical Society of the Pacific by Astronomical Society of the Pacific (1919)
"... it was the most powerful instrument ever constructed. Very respectfully, (signed) AMBROSE SWASEY. THE focal length OF THE 36-INCH REFRACTOR In Dr. ..."

6. Manual of Petrographic Methods by Albert Johannsen (1918)
"Many instruments are so arranged that the tube is capable of adjustment to different lengths. 102. focal length. — The focal length of the compound ..."

7. A Handbook of Physics Measurements by Ervin Sidney Ferry, Oscar William Silvey, George William Sherman, David Christie Duncan (1918)
"The difference between the readings of P and p is the principal focal length of the diverging lens under test. Exp. 33. Location of the Equivalent Points ..."

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