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Lens calculator - Calculating the focal length


The focal length f´ virtually serves to calculate the required lens and is thus the most important specification to characterise an (entocentric) normal lens.

f' = g / (G/B + 1)
Optik Berechnung Brennweite


The theoretic value of the focal length calculation serves to find the best suitable optics. Typical increments of focal lengths for C-mount lenses are e.g. (1.8, 2.8, 4, 6,) 8, 12, 16, 25, 35, 50 and 75 mm.

Note: Even when using the drop-down lists own values can be entered. Please use the first entry "user def."!


Sensor size :
Length of inspected part in mm (field of view FOV):
Working distance in millimeters:



Calculated focal length of lens:


Attention: Calculated focal lengths below 1.4 mm or beyond 500 mm are declared unrealistic. Extreme values are nevertheless displayed. Please observe that very small working distances below the close-up limit can only be realised using additional close-up rings. In the extremely close range (few cm), the focal lengths cannot be calculated precisely due to simplified approximate computation and unknown dimensions of the lenses. Please use macro-lenses for this purpose!

Further details on optical calculations, such as the focal length calculation, can be found in chapter Optical basics.

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