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Lens calculator - Calculating the working distance g

The object distance refers to the distance between the object ("test object", "scene", also "field of view") and the first principal plane of the lens groups somewhere in the optical system. The often wanted, so-called "free working distance", from the test object to the front surface of the lens can only be calculated by specifying the position and distance of the two principal planes and the real lens length. This means that the "working distances" calculated here are only approximate values.

Method 1
classic
g= f´* (G /B +1)
Method 2
using object size
& opening angle

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


g= f´* (G /B +1)

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


Sensor size :
Focal length:
Length/ size of inspected object in mm (field of view FOV):


Calculated working distance:



Calculating the working distance using object size and opening angle

Object size / field of view in mm:
Opening angle of lens:


Needed working distance:


Attention: Calculated working distances below 150 to 300 millimetres cannot be focused using normal C-mount lenses. In case of F-mount lenses and other lenses for larger image circle diameters, the minimum lens distances are often considerably larger. By means of additional spacers, however, the lens distance can be reduced ("see calculation of close-up rings"). The calculated working distances refer to the optic centre of the lens housing. Especially in case of very small working distances of several centimetres, the calculated values are no longer realistic. In case of smallest image details and large magnifications please use macro-lenses which are specially designed for these applications.

Further details on optical calculations can be found in chapter Optical basics.

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