Formula for Focal Length
The formula for focal length is:
= lens focal length in millimeters
= camera scale factor (see Camera Scale Factors)
= camera height (distance from front of lens to work surface)
= height of camera field-of-view (same units as 
)
Camera Scale Factor illustrates these relationships and the meaning of the camera scale factor. In the two examples in this illustration, the field-of-view width and the camera-to-object distance remain constant while two cameras with different size imaging surfaces are used. In order to keep the image within the imaging surface on both cameras, different focal length lenses must be used. By applying the correct camera scale factor for each camera (based on the imaging surface size), the correct lens focal length can be determined.
The following formula shows the relationship between resolution and image size for AdeptVision VXL (EVI board) and AdeptVision AVI systems.