Focal Length Calculator

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R₁ (mm): OR Plano R₂ (mm): OR Plano Object Space Index, n_OS: Lens Index, n_L: Image Space Index, n_IS: Center Thickness, CT (mm):

Effective Focal Length, EFL (mm): --

Back Focal Length, BFL (mm): --

Front Focal Length, FFL (mm): --

Primary Principal Point, P (mm): --

Secondary Principal Point, P'' (mm): --

Shift in Nodal Point (mm): >--

$$ \Phi_{\text{OS}} = \frac{n_L - n_{\text{OS}}}{R_1} $$

$$ \Phi_{\text{IS}} = \frac{ n_{\text{IS}} - n_{L} }{R_2} $$

$$ \Phi = \Phi_{\text{OS}} + \Phi_{\text{IS}} - \Phi_{\text{OS}} \, \Phi_{\text{IS}} \, \left( \frac{\text{CT}}{n_L} \right) $$

$$ P'' = - \frac{\Phi_{\text{OS}}}{\Phi} \, \left( \frac{n_{\text{IS}}}{n_L} \right) \, \text{CT} $$

$$ \text{EFL} = \frac{1}{\Phi} $$

$$ f_F = - n_{\text{OS}} \cdot \text{EFL} $$

$$ f_R = n_{\text{IS}} \cdot \text{EFL} $$

$$ \text{BFL} = f_R + P'' $$

$$ \text{FFL} = f_F + P $$

$$ \text{NPS} = f_F + f_R $$

$$ P = \frac{\Phi_{\text{IS}}}{\Phi} \, \left( \frac{n_{\text{OS}}}{n_L} \right) \, \text{CT} $$

Φ_OS	Power of Surface 1
Φ_IS	Power of Surface 2
F	Lens Power
n_OS	Object Space Index
n_L	Lens Index
n_IS	Image Space Index
R₁	Radius of Surface 1
R₂	Radius of Surface 2
CT	Center Thickness

P	Primary Principle Point
P"	Secondary Principle Point
EFL	Effective Focal Length
BFL	Back Focal Length
FFL	Front Focal Length
NPS	Nodal Point Shift
f_F	Front Focal Point
f_R	Rear Focal Point

Notes:

Please use the American standard for number formatting rather than the European standard (i.e. for "two and a half," enter "2.5" rather than "2,5").
This calculator follows the standard sign convention for the optical radius of curvature where if the vertex of a surface lies to the left of the center of curvature the radius of curvature is positive, and if the vertex lies to the right of the center of curvature the radius of curvature is negative. In the figure, R₁ is positive and R₂ is negative.

Description

Relate optical and mechanical parameters of simple lenses in order to ease integration into application assemblies. Select index from list of Edmund Optics' own optical substrates to help calculate focal lengths and principal points of any standard lens.

Application Note

Understanding Focal Length and Field of View

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Related Product Category: Optical Lenses

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