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# Lens calculator - Calculating the working distance a

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.

classic
a= f´* (y /y´ +1)
using sensor information
using object size
& opening angle

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

a= f´* ( y / y´ +1)

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

 Sensor size : User def. (mm) 1/4" 3.2 mm 1/3" 4.8 mm 1/2.5" 5.7 mm 1/2" 6.4 mm 1/1.8" 7.2 mm 2/3" 8.8mm 10.5 mm 1" 12.8 mm 1.2" 14.2 mm 15.3 mm 4/3 17.9 mm APS/C 23.7 mm KB 36.0 mm Line .5K 14µm Line 1K 10µm Line 1K 14µm Line 2K 10µm Line 2K 14µm Line 4K 7µm Line 4K 10µm Line 6K 7µm Line 8K 7µm Line 12K 5µm Focal length: User def. (mm) 2.8 3.2 4.8 6 8 9 12 16 17 23 25 35 50 60 75 85 100 125 150 Length/ size of inspected object in mm (field of view FOV): Calculated working distance:

## Arbeitsabstand: mit Pixelgröße Sensor, Brennweite und Bauteilgröße rechnen

Hinweis: Zur einfachen Berechnung bitte einen Wert in der Dropdownbox selektieren! Eingabe eigener Werte durch Auswahl von "User def.." in DropDown-Liste!

 Sensor pixel count in X direction: User def. (px) 240 px 320 px 480 px 512 px 640 px 800 px 1024 px 1200 px 1280 px 1400 px 1600 px 2048 px 2452 px 3200 px 4096 px 4872 px 6144 px 8192 px 12288 px Sensor pixel count in Y direction: Userdef. (Px) 240 px 320 px 480 px 512 px 640 px 800 px 1024 px 1200 px 1280 px 1400 px 1600 px 2048 px 2452 px 3200 px 4096 px 4872 px 6144 px 8192 px 12288 px Pixel size in µm: User def. pixel size (µm) 1 µm 1.7 µm 2 µm 2.2 µm 3 µm 3.45 µm 4 µm 4.4 µm 5 µm 5.3 µm 6 µm 7 µm 8 µm 10 µm 14 µm 20 µm Focal length of lens: User def. (mm) 2.8 3.2 4.8 6 8 9 12 16 17 23 25 35 50 60 75 85 100 125 150 Object length in mm: Object width in mm: Object diagonal in mm: Calculated sensor dimensions: Calculated sensor ratio: 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:

## Send data by email

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.