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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.

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.

classic
f' = g / (G/B + 1)
using sensor information

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

## Send data by email

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: 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: Userdef. Pixelgröße 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 Working distance in mm: Object length in mm: Object width in mm: Object diagonal in mm: Calculated sensor dimensions: Calculated sensor ratio: Focal length:

## Send data by email

Further details on optical calculations, such as the focal length calculation, can be found in chapter Optical basics. + "\n----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n" + "\n Vision Doctor does ot provide customer support!\n If you need ADVICE for a PROJECT or a DETAILED QUOTE, please copy This email address is being protected from spambots. You need JavaScript enabled to view it. into this mail to send our commercial partner a summary of your compilation as a basis for discussion.\n We assure you that phi-vision will not receive any information other than what you see on your email before sending it. \n"