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Calculating the focal length f´

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

Calculating the focal length using sensor size, working distance and object size

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


Sensor size :
Working distance in millimeters:

Length of inspected part in mm (field of view FOV):
Calculated focal length of lens:


We respect your privacy: we do not store any input, results or recipients. Send yourself your calculation with your own email program (MailTo-Link).

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!


Focal length: Calculate with information of pixel sizes

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

Sensor pixel count in X direction:
Sensor pixel count in Y direction:
Pixel size in µm:
Working distance in mm:
Object length in mm:
Object width in mm:
Object diagonal in mm:
Calculated sensor dimensions:
Calculated sensor ratio:
Focal length:


We respect your privacy: we do not store any input, results or recipients. Send yourself your calculation with your own email program (MailTo-Link).

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

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