The selection formula of industrial lens (attached CCD chip size table)

The focal distance(f mm) of industrial lens can be calculated by FOV,WD and CCD chip size:
FOV stands for the size of incepted object, and the size of FOV is ensured by WD, lens focal distance and CCD chip size.
1.The calculation of focal distance, FOV size, WD and optical magnification is as below:
Focal Distance f=WD x CCD chip size(H or V)/ FOV( H or V)
FOV ( H or V)= WD × CCD chip size( H or V) / focal distance f
FOV ( H or V)= WD × CCD chip size( H or V) / optical magnification 
WD=focal distance f x CCD chip size/FOV( H or V)
Optical magnification= CCD chip size (H or V) / FOV( H or V)

2.CCD chip size table:

1.1 feet--target size is: width 12mm* height 12mm, diagonal 17mm
1 foot --target size is: width 12.7mm* height 9.6mm, diagonal 16mm
2/3 feet--target size is: width 8.8mm* height 6.6mm, diagonal 11mm
1/1.8 feet--target size is: width 7.2mm* height 5.4mm, diagonal 9mm
1/2 feet--target size is: width 6.4mm* height 4.8mm, diagonal 8mm
1/3 feet--target size is: width 4.8mm* height 3.6mm, diagonal 6mm
1/4 feet--target size is: width 3.2mm* height 2.4mm, diagonal 4mm