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Koehler Illumination Calculator

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Source Diameter (mm):

Lens 1 Diameter (mm):

Lens 1 Focal Length (mm):

Lens 2 Diameter (mm):

Lens 2 Focal Length (mm):

Source to Lens 1 Distance (mm): --     

Lens 1 to Lens 2 Distance (mm): --     

Lens 2 to Spot Diameter Distance (mm): --     

System Length (mm): --     

Spot Diameter (mm): --     

Input Numerical Aperture, NA: --     

Output Numerical Aperture, NA: --     

Focal Length Calculator
$$ d_1 = \text{FL}_1 \left[ \frac{D_{\text{Source}} + D_{L_2}}{D_{L_2}} \right] $$
$$ d_2 = \frac{d_1 \, \text{FL}_1}{d_1 - \text{FL}_1} $$
$$ d_3 = \frac{d_2 \, \text{FL}_2}{d_2 - \text{FL}_2} $$
$$ \text{System Length} = d_1 + d_2 + d_3 $$
$$ D_{\text{Spot}} = \frac{D_{L_1} \, \text{FL}_2}{d_2 - \text{FL}_2} $$
$$ \text{NA}_{\text{Input}} = \sin{\left[ \tan^{-1}{\left( \frac{D_{L_1}}{2 d_1} \right)} \right]} $$
$$ \text{NA}_{\text{Output}} = \sin{\left[ \tan^{-1}{\left( \frac{D_{L_2}}{2 d_3} \right)} \right]} $$
d1 Source to Lens 1 Distance
d2 Lens 1 to Lens 2 Distance
d3 Lens 2 to Spot Distance
DL1 Diameter of Lens 1
DL2 Diameter of Lens 2
FL1 Focal Length of Lens 1
FL2 Focal Length of Lens 2
Dsource Source Diameter
Dspot Spot Diameter
NAinput Input Numerical Aperture
NAoutput Output Numerical Aperture


Mathematically determine how to configure a source and two lenses into a Koehler Illumination setup. Calculator uses the paraxial lens approximation and enables an initial lens selection. Once lenses are selected, EO recommends modeling one's Koehler Illumination setup in optical design software such as Zemax, CodeV, or FRED to analyze and revise as needed. Please note that performance will vary based on source and lens selections.

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