The magnification β is defined as: 

{!{!{\beta=\frac{sensor\ length}{ROI\ length}=\frac{S}{L}=\frac{a'}{a}}!}!}


ROI length      L = 290 mm 
Sensor length      S = 28.7 mm
Magnification        β = S/L = 28.7/290 = 1/10.1 = 0.099

Imaging Parameters

Schematic depiction of the imaging system and definition of variables used.

f = Lens focal length (mm)
S = Sensor length (mm)
L = Length of Region of Interest (ROI) of object (mm)
a = Object range (mm)
a’ = Image distance: Distance from sensor to HH’ (mm)
β Magnification
w = Field angle
OO’ = Distance from sensor to measured zone (mm)
s’A = Flange focal length (mm)
∆s’  = Lens extension (mm)
LT = Tube length 
A = Working distance (mm)
HH’ = Principal point distance (mm) (can lengthen or shorten OO’)
s’K = Camera flange length consisting of focus adapter series FA22 and extension rings series ZR (mm)
LO = Lens length (mm)